Light and architecture

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LIGHT AND ARCHITECTURE
By
Ranjali.A
A Dissertation Submitted to the Faculty of the
SCHOOL OF ARCHITECTURE
MEENAKSHI COLLEGE OF ENGINEERING
2013

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CONTENTS
LIST OF FIGURES......................................................................................................................................5
CHAPTER I :..............................................................................................................................................6
1.0 INTRODUCTION.................................................................................................................................6
1.1 LIGHT AND LIGHTING........................................................................................................................6
1.2 PURPOSE OF LIGHTING .....................................................................................................................6
1.3 NATURAL / DAY LIGHTING AND ARTIFICIAL LIGHTING - INTRODUCTION.........................................7
1.4 DAY LIGHTING AND SUN LIGHTING - COMPARISON.........................................................................8
1.5 LIGHT IN THE ASPECT OF CLIMATE RESPONSIVE ARCHITECTURE.....................................................9
1.6 Summary.........................................................................................................................................11
CHAPTER II : THEORETICAL FRAMEWORK AND LITERATURE REVIEW..................................................12
2.0 Luminous Efficacy .......................................................................................................................12
2.1 GLARE..............................................................................................................................................13
2.2 GLARE PROBLEMS...........................................................................................................................14
2.2.1 DISABILITY GLARE.....................................................................................................................14
2.2.2 DISCOMFORT GLARE................................................................................................................14
2.2.3 VEILING REFLECTIONS..............................................................................................................14
2.2.4 REFLECTED GLARE....................................................................................................................14
2.2.5 VISUAL COMFORT ....................................................................................................................15
2.3 DEGREE OF ENCLOSURE..................................................................................................................15
2.4 DAYLIGHTING - ADVANTAGES.........................................................................................................15
2.5 DAY LIGHTING - DISADVANTAGES ..................................................................................................16
2.6 STRATEGIES AND ELEMENTS...........................................................................................................17
Windows........................................................................................................................................17
2.6.1 Skylights ...................................................................................................................................19
2.6.2 Saw-tooth Skylights / North lights ...........................................................................................19
2.6.3 Roof Monitor............................................................................................................................20
2.6.4 Atrium ......................................................................................................................................21
2.7 CASE STUDY: Le Corbusier’s Chapel at Ronchamp.........................................................................22
2.8 CASE STUDY : LAURIE BAKER’S CENTER FOR DEVELOPMENT STUDIES – TRIVANDRUM , KERALA,
INDIA.....................................................................................................................................................24
2.8.1 Main features of this building:.................................................................................................24

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2.9 CASE STUDY: TADAO ANDO ‘S CHURCH OF LIGHT, IBARAKI, OSAKA, JAPAN .................................26
2.10 FENESTRATION - THE IMPORTANCE OF WINDOWS .....................................................................29
2.11 GLASS – AN INTEGRAL PART OF WINDOW ...................................................................................29
2.11.1 ENERGY EFFICIENT GLAZING..................................................................................................31
2.12 APPLICATIONS OF DAY LIGHTING STRATEGIES.............................................................................31
2.12.1 BUILDING DESIGN ..................................................................................................................31
2.12.2 INFLUENCE OF THE SIZE OF THE APERTURES.........................................................................32
2.12.3 INFLUENCE OF SIZE AND GEOMETRY OF APERTURE .............................................................32
2.12.4 INFLUENCE OF WINDOW FRAME...........................................................................................32
2.12.5 INFLUENCE OF LUMINOUS TRANSMITTANCE........................................................................33
2.12.6 INFLUENCE OF SLOPE OF APERTURE .....................................................................................33
2.12.7 INFLUENCE OF GLAZING CLEANLINESS..................................................................................33
2.12.8 INFLUENCE OF DIMENSION OF THE ROOM ...........................................................................33
2.12.9 INFLUENCE OF ARRANGEMENT OF FURNITURE....................................................................34
2.12.10 INFLUENCE OF COLOUR & COEFFICIENTS OF REFLECTION OF THE ROOM .........................34
2.13 ALTERNATE GLAZING MATERIALS.................................................................................................34
2.13.2 Advantages:............................................................................................................................35
2.13.3Properties: ..............................................................................................................................35
2.15 FUTURE OF ALTERNATE GLAZING MATERIAL ...............................................................................38
CHAPTER III : METHODOLOGY ..............................................................................................................39
3.0 CALCULATIONS AND THUMB RULES...............................................................................................39
3.1 Daylight factor (DF).....................................................................................................................39
3.2 Climate-based daylight metrics (CBDM).....................................................................................41
3.3ECOFRIENDLY LIGHTING – ARTIFICIAL LIGHTING.............................................................................42
3.3.1 CFL LIGHTS (compact fluorescent lights) .................................................................................42
3.3.2 LED LIGHTS (Light emitting diode) ...........................................................................................43
3.3.3 Size and Efficiency....................................................................................................................44
3.3.4 Long Life...................................................................................................................................44
3.3.5 Lower Temperatures................................................................................................................44
3.3.6 nergy Star LEDs ........................................................................................................................44
3.4 ENERGY EFFICIENCY – NATURAL LIGHTING ....................................................................................45
3.4.1 SMART GLASS...........................................................................................................................45
3.4.2 Strength....................................................................................................................................46
3.4.3 Noise protection ......................................................................................................................46

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3.4.4 Advantages of SPD Smartglass.................................................................................................46
3.4.5 Roof lights: ...............................................................................................................................47
3.5 CASE STUDY : The Brew House Hotel, Kent, London ......................................................................47
3.6 FIBRE OPTIC CONCRETE WALL ........................................................................................................48
3.7TECHNOLOGIES................................................................................................................................49
3.7.1 ACTIVE DAY LIGHTING..............................................................................................................49
3.7.2 Types of active day lighting control systems ...........................................................................50
3.7.3 PASSIVE DAY LIGHTING................................................................................................................50
3.8 HELIOSTATS.....................................................................................................................................51
3.9 TUBULAR DAY LIGHTING DEVICES ..................................................................................................53
3.9.1 Solar and hybrid lighting systems ................................................................................................53
CHAPTER IV: ..........................................................................................................................................55
4.0 CONCLUSION...................................................................................................................................55
BIBLIOGRAPHY ......................................................................................................................................57

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LIST OF FIGURES
Figure 1 : Sun lit space..............................................................................................................9
Figure 2 : Day lit space .............................................................................................................9
Figure 3 : - Cross section shows lighting distribution from a single-sided window
installation. ..............................................................................................................................17
Figure 4 : Day light penetration..............................................................................................18
Figure 5 : Lighting distribution with windows on two sides ...................................................18
Figure 6 : light shelves ............................................................................................................18
Figure 7 : Cross section showing how illumination vectors become more horizontal as
sidelight travels deeper into a space........................................................................................19
Figure 8 : Effect of skylight on Day light distribution.............................................................19
Figure 9 : Day light distribution due to a saw tooth roof lighting system ..............................20
Figure 10 : Day lighting distribution due to a raised roof monitor ........................................20
Figure 12..................................................................................................................................21
Figure 11..................................................................................................................................21
Figure 13 Interior of Notre Dame du haut (looking up)..........................................................22
Figure 14 : Center for development studies ............................................................................25
Figure 15 : Alternate glazing material ....................................................................................34
Figure 16 : smart glass application as a partition .................................................................48
Figure 17 : Smart glass turning out to be a normal glass partition........................................48
Figure 18 : Human standing behind a fibre concrete wall. Image describes the translucent
nature of material ....................................................................................................................49
Figure 19 : Heliostat with mirror on open space ....................................................................52
Figure 20 : Cost reduction graph for heliostats & Titan trackers. .........................................52
Figure 21 : Tubular day lighting devices ................................................................................53

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CHAPTER I :
1.0 INTRODUCTION
‘There is no need to define what natural light is, but we do need to remember that this light
allows us to define what is around us, by day and night: the changing perception of the things
or the bodies on which it impacts, and the space that contains them. Light, or absence of
light, can also transform this space in each season, each day of the year, each hour of the
day, each moment.’(Light and Architecture,Cesar Portela)
The dictionary Microsoft® Encarta® 2009 defines light as –‘ Light is a natural agent that
stimulates sight and makes objects visible. It is a source that illumines everything’.
Light, in other terms, “...is something that defines anything that we see. It shows us the
colour, the boundary, the texture, of anything that is visible. Light cannot be seen. It is only
inferred.” This element is used everywhere and has its importance subtly placed in
Architecture. It’s influence varies from physical to psychological or even spiritual. The
colour of an object we tend to perceive is a resultant of absorption of light by the object. The
psychological graph slopes up to a great extent when the perceiver enters a brighter space
from a dull space.
fenestration
1.1 LIGHT AND LIGHTING
Light and lighting are commonly used terms, where the crowd usually forgets their distinct
difference, that is light is a source from which any object gets illuminated. Light helps us
visibly identify objects. Whereas lighting is the phenomena. It is generally said to be the
equipment or amount of light/source requirement that is fulfilled.
1.2 PURPOSE OF LIGHTING
The purpose of lighting a space is twofold –
1. Functional - to facilitate the performance of a visual task and ensure visual concept.
2. Aesthetic- to create certain emotional effects.

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In architectural context, both natural and artificial lighting contribute to the ambience of
space, fulfilling both functional and aesthetic purposes.
Choice of lighting for a place varies with respect to the type of place, its scale and the
psychology of people accessing it.
1.3 NATURAL / DAY LIGHTING AND ARTIFICIAL LIGHTING -
INTRODUCTION
Lighting is differed from light. Lighting gets described this way, ‘An external sourcing
through which the space is lit’. Lighting has been classified into artificial and day lighting.
Natural lighting refers to the admittance of light from the sky into internal spaces and is a key
factor in the design of energy efficient commercial buildings. Properly used, it can result in
substantial energy savings by reducing the need for artificial lighting. The primary aim of
natural lighting is to provide sufficient light under all circumstances for the tasks performed
within a space. If such a lighting level cannot be achieved by natural light alone, then
localised artificial task lighting can be used to supplement.
At first, it seems obvious that we provide lighting to enable people to see, so that all lighting
can be assessed in terms of how well it enables people to see. Lighting that maximizes the
luminance contrast of visual detail enables very small detail to be accurately detected, and
this is the basis of many lighting recommendations and standards. However, observation of
our surroundings shows a much larger range of ways in which objects can differ in
appearance. Consider for a moment the judgements that we commonly make in deciding
whether a surface is clean and dry; whether fresh fruit is good to eat; or whether a colleague
looks tired. These judgements are based on observation of appearance, but what are the
differences of appearance that are critical in making these judgements? Any of these
everyday assessments of appearance can be influenced by subtle aspects of lighting, and so
too can our more complex assessments of the appearance of architectural spaces.
Now artificial lighting is the artificially sourced/externally sourced lights that Is intended to
illuminate an area or simply highlight an element.
The purpose of artificial lighting is threefold:
1. To lit the space in the absence of day lighting.
2. To emphasise a feature
3. For ambient illumination.

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Ambient illumination is the overall brightness, illumination and colour appearance.
Artificial lighting are purposefully done in areas where the space needs a highlight.
This shall mean, the artificial lighting differs from each area. Few lighting are based on
luxury look. Few are for necessity. So the purpose is to light the space with apt lighting.
The amount of light incident on a surface per unit area is illuminance.
Different sources of illumination vary significantly with respect to the quality of light they
provide. Quantity of light influences Quality of light— or more specifically, by the
relationship between the brightness of a light and one’s distance from it. Light becomes more
diffuse farther away from the source, so for a given brightness, there is a range of heights
within which the source should be located to create the desired quality of light.
‘A basis of theory enables designers to examine their own observations of the things
that surround them. Differences of object appearance have their origin in the physical
processes by which light is reflected, refracted, dispersed and scattered by matter. But
human vision did not evolve to enable us to observe these processes: it evolved to
enable us to recognize our surroundings.’ (Lighting by design, Christopher cuttle)
Understanding of the roles of these processes requires directed observation, and when we
apply observation analytically, we find that the number of physical processes that is
responsible for all of the differences that we can discriminate is quite limited. With this
insight, we start to gain knowledge of how to control light to achieve a visible effect that we
have in mind. It is, in fact, quite remarkable how the astounding range of human visual
sensations is governed by so few processes. Lighting is both the medium that makes things
visible, and a visible medium. At one level it reveals the identifying attributes that enable us
to recognize the objects that surround us, and at another level it creates patterns of colour, and
light and shade, which add other dimensions to the visual scene. This chapter examines the
role of lighting at the former level, that is to say, its role in making visible the aspects of
appearance that enable us to perceive our surroundings. We start by considering what we
need to know about the processes of vision and visual perception.
1.4 DAY LIGHTING AND SUN LIGHTING - COMPARISON
Day lighting does not equal sunlight! Day lighting is about bringing natural light into a space.
Many day lit spaces do not want or need direct sunlight. Daylight refers to the level of diffuse
natural light coming from the surrounding sky dome or reflected off adjacent surfaces.
Sunlight, on the other hand, refers to direct sunshine and is very much brighter than ambient

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daylight. The Sun's position in the sky varies markedly throughout the day and, when viewed
from any particular point, is often obscured by clouds, trees or other buildings. It also
experiences significant changes in intensity at different times of the year. Thus it does not
make a very reliable light source with which to light the inside of a building. Also, its
intensity is such that it can be a significant source of glare when falling on a work surface or
reflected off a computer screen. As a result, direct sunlight is rarely included in architectural
day lighting calculations.
Figure 1 : Sun lit space Figure 2 : Day lit space
Illustration – 1(a) Illustration – 1(b)
Illustration 1(a) shows the sun lit space and Illustration 1(b) portrays the day lit space.
(Image courtesy: http://wiki.naturalfrequency.com).
Daylight, however, can be a very effective light source, even on the most dark and overcast
day. Daylight levels can also be quite variable and depend on the amount or type of cloud in
the sky and the time of day. However, there exist a range of mathematical models that allow
the calculation of how bright different parts of the sky will be under different sky conditions.
These models allow us to choose a set of worst-case situations around which to design the
building.
1.5 LIGHT IN THE ASPECT OF CLIMATE RESPONSIVE
ARCHITECTURE
‘It is recommended that many openings be used on the southern facade and only those
openings to be used on the northern facade which are absolutely essential. It is advisable to

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avoid openings on the eastern and western facades’.( CLIMATE RESPONSIVE
ARCHITECTURE. – a design handbook for energy efficient buildings.)
The physical meaning of daylight is radiation in a wavelength range of 0.4 – 0.7 micron.
Studies have shown that increasing the window area above 1/8 or 1/10 of the area of the floor
space does not increase the average intensity of the lighting linearly. For centuries the design
of buildings to admit daylight has been fundamental to architecture. Surely the window is one
of the most important and expressive visual elements of a building seen from inside or
outside. only in the last few decades with the development of relatively cheap energy and
efficient lighting, ( a lumen of artificial light is about 500units cheaper today, in real terms
than at the beginning of the century) has the option of artificial light as an alternative to
daylight been considered. This has led to deep plan buildings and ultimately to the
abandonment of the natural outdoor environment to provide light and ventilation.
The most efficient way, in principle of lighting a building in the daytime, is to admit daylight.
This is for two reasons
1 – The ‘luminous efficacy’ – i.e. the useful visible light in relation to the total energy of the
radiation is high. – The heating effect of daylight is about 1W per 100m, between ½ and 1/10
of typical artificial lighting alternatives.
2- Daylight is free. Artificial lighting consumes electricity, usually ‘on-peak’ electricity and
larger buildings often constitute the largest single category of energy cost.
A further benefit of daylight is that it usually implies a good visual link between indoors and
outdoors. There is increasing evidence that this quality is essential for the well being of
occupants, especially in larger non domestic buildings.
Three main disadvantages of day lighting are:
1. Artificial lighting has to be provided for occupation during the hours of darkness.
2. The source of light – i.e. the sky, varies in its brightness over a wide range. Windows
which are sized to provide sufficient daylight in dull sky conditions and may admit
direct sun at times.
3. If the daylight is admitted from the side of a room, illumination levels close to the
window will normally be much higher than necessary in order to achieve sufficient
levels in the darkest part of the room.

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Since a day lighting system operates differently than a system used in a conventional
building, occupants should be trained on the operation of the switches (if any are provided),
on the overall design intent, and on the expected functionality of the day lighting system. In a
conventional building, lights are typically on all the time whether they are needed or not.
Therefore, if users are better informed about the building’s design and operational goals, they
will likely make a greater effort to operate the building properly, and to communicate when
the lighting does not work as expected.
1.6 Summary
This chapter introduces light and its behaviour. Further discussions on the classifications such
as day lighting and artificial lighting have been documented. The research limits itself in
‘light in the aspect of climate responsive architecture’ in the basic applications of light and its
requirement for a region.

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CHAPTER II : THEORETICAL FRAMEWORK AND LITERATURE
REVIEW
2.0 Luminous Efficacy
Luminous flux is the rate of emission of light evaluated by the visual sensation it produces.
(Microsoft® Encarta® 2009) Lumen is the unit to measure light. The unit of luminous flux,
equal to the amount of light crossing a unit area at a unit distance from a light source of
luminous intensity of one candela. Light and heat normally come together, however the
amount of heat produced by different lights for the same lighting intensity can vary
significantly. It turns out that, in terms of the number of lighting lumens per watt of heat
energy, diffuse daylight is about 5 times more efficient than a normal incandescent globe and
as much as twice as efficient as a fluorescent tube. In a typical office building, turning the
lights off and substituting daylight alone can reduce overall heat loads by as much as 40%,
principally by reducing over-illumination near peripheral windows.
Table 1 - Efficacy of various forms of daylight and electric lamps.
Light Source
Efficacy
(lumens/Watt)
Direct Sun (low altitude) 90 lm/w
Direct Sun (high altitude) 117 lm/w
Direct Sun (mean altitude) 100 lm/w
Diffuse Sky (clear) 150 lm/w
Diffuse Sky (average) 125 lm/w
Global (average of sky and sun) 115 lm/w
Incandescent (150 w) 16-40 lm/w
Fluorescent (40 w, CWX) 50-80 lm/w
High Pressure Sodium 40-140 lm/w
(Source: http://wiki.naturalfrequency.com/wiki/Daylight_Sunlight)
Table 1 above shows that the luminous efficacy of direct sunlight is also much greater than
that of most commonly used electric alternatives. However, it is also considerably brighter so
it will introduce significant heat gains if allowed to enter the building directly at the wrong
time of year. Obviously in many climates this heat gain may be welcomed in winter. This
requires the careful use of shading devices and light diffusers to properly protect against
direct summer sun penetration whilst distributing natural light deep into each space. Careful
selection of glass type is also an important factor. However, the most important factor in day
lighting design is the selection of the most appropriate type of apertures through which each
space will connect to light from outside.

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A day lighting system is comprised not just of daylight apertures, such as skylights and
windows, but is coupled with a daylight-responsive lighting control system. When there is
adequate ambient lighting provided from daylight alone, this system has the capability to
reduce electric lighting power. Further, the fenestration, or location of windows in a building,
must be designed in such a way as to avoid the admittance of direct sun on task surfaces or
into occupants’ eyes. Alternatively, suitable glare remediation devices such as blinds or
shades must be made available. Glare shall be defined as the excessive brightness that gives
visual discomfort.
Implementing day lighting on a project goes beyond simply listing the components to be
gathered and installed. Day lighting requires an integrated design approach to be successful,
because it can involve decisions about the building form, site, climate, building components
(such as windows and skylights), lighting controls, and lighting design criteria.
2.1 GLARE
There are two main types of glare. The first occurs when the eye has adapted to an
environment over time and the environment undergoes rapid change. The other occurs when
the eye has adapted to an environment and a source of light appears that is much brighter than
anything else around it.
The first case almost always occurs when the iris is wide open because it has adapted to very
low light levels. The most obvious example of this occurs when leaving a dark space and
suddenly entering bright sunlight. The iris adjusts rapidly, but not without some discomfort
and lack of visual acuity during the adjustment. The eye will also adjust from a very bright
environment to a very dark one, but not as rapidly. It takes much longer for the eye to adapt
to a very dark environment, sometimes as long as 10-15 minutes. The severity of this form of
glare depends on the time taken for the environment to change and the degree of change.
Large changes that occur slowly will not usually result in a glare problem.
The second form of glare occurs because the iris adjusts to the overall level of brightness over
the entire field of view. This means that in a dark room, the iris will open wide. If there is just
one point of light within the field of view, the average brightness will still remain relatively
low. However, that one point will be effectively burning a hole in the retina at the point of
focus. Fortunately, this is associated with some discomfort, usually prompting us to make an
adjustment to protect the eye. This may involve turning away, squinting, or simply correcting

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the environment (turning the light off or pointing it the other way). Such an automatic
adjustment can be consciously overridden, such as squinting and looking directly at the sun.
However, this is extremely detrimental to the retina and can cause permanent damage.
Glare may also occur as a result of a reflection coming from a very bright source outside the
field of view. The reflection may cause discomfort as well as the additional annoyance of
veiling or masking out the information which is being sought within that view.
2.2 GLARE PROBLEMS
2.2.1 DISABILITY GLARE
Brilliant light sources, like car headlamps at night, or the view of the sun from a window at
the end of a corridor are examples of this sort of discomfort.
2.2.2 DISCOMFORT GLARE
Glare in which there is no significant reduction in the ability to see, although discomfort still
persists, due to the bright sources in the field of view is called discomfort glare. e.g. the view
of an excessively bright sky near the line of sight of a person.
2.2.3 VEILING REFLECTIONS
Veiling reflections are caused when the reflected image of a source of light is brighter than
the luminance of the task, e.g. the image of a window off the surface of a computer screen.
Pencil handwriting where the graphite acts as a mirror is more susceptible to veiling
reflections than other types of ink.
2.2.4 REFLECTED GLARE
When light from a light source is reflected off specular surfaces into the eye or field of view,
it is called reflected glare. An example would be the discomfort produced by the sun
reflection from a swimming pool.
In order to determine, on a scientific basis, the necessary standards of lighting in a building, it
is necessary to break down the characteristics of visual comfort, visual acuity and task, and
express this relationship in terms of brightness, contrast ratios and adaptation levels. These
have been the basis of methods of glare evaluation to date.

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2.2.5 VISUAL COMFORT
Visual comfort is taken to mean the absence of physiological pain, irritation or distraction.
Visual comfort within a space depends on the contrast levels and luminance variations across
the space.
Glare is one of the most common causes of visual discomfort and can result in the occupant
having to interact with the lighting system. Occupant interaction with lighting and lighting
control systems can significantly impact the energy use patterns of spaces. If issues of glare
and visual discomfort are understood during the initial design process, they could be designed
for and hence affect predicted energy requirements. (whole building design guide,
www.wbdg.org)
With the building sited properly, the next consideration is to develop a climate-responsive
window-to-wall area ratio. As even high-performance glazing’s do not have insulation ratings
close to those of wall constructions, the window area needs to be a careful balance between
admission of daylight and thermal issues such as wintertime heat loss and summertime heat
gain. The American Society of Heating, Refrigerating, and Air Conditioning Engineers
(ASHRAE) offers guidance on these ratios per climate zone in their Standard 90.1 energy
code, but these are primarily minimal for thermal performance and do not consider admission
of daylight.
2.3 DEGREE OF ENCLOSURE
The degree of enclosure of a space as determined by the configuration of its defining
elements and pattern of its opening has a significant impact on our perception of its form and
orientation. From within a space we see only the surface of a wall. It is this thin layer of
material that forms the vertical boundary of a space. The actual thickness of wall plane can be
revealed only along the edges of doors and windows.(Form,Space and Order, 172,
Francis.D.K.Ching)
2.4 DAYLIGHTING - ADVANTAGES
The overall objective of day lighting is to minimize the amount of artificial light and reduce
electricity costs, but it can also lower HVAC costs as well. Electrical lighting produces a lot
of heat, whereas, if properly controlled, natural lighting generates hardly any heat at all.

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For most buildings incorporating day lighting, the overall energy savings range from 15 to 40
percent. Although energy savings and sustainability may be the reasons companies initially
opt for day lighting, it can also have an impact on the productivity and satisfaction of
employees, students and even clients and retail customers.
People have a natural attraction and need for daylight. Studies suggest that day lighting has a
direct impact on well-being, productivity and overall sense of satisfaction. Even retail stores
have seen the environmental and monetary benefits of day lighting for both employees and
consumers. In an experiment, stores that included skylights over certain departments found
that overall sales per square foot were higher in the departments lit by natural light.
( http://www.facilitiesnet.com)
2.5 DAY LIGHTING - DISADVANTAGES
Although day lighting can provide numerous positive results in regards to worker
performance, if a day lighting program has not been executed properly, it can produce
negative results. A few strategies can help facility executives overcome the challenges of day
lighting.
A high-performance day lighting system may initially require a significant investment.
However, if the project team uses an integrated, strategic design approach, a company’s
overall long-term savings make up for any initial dollars spent on day lighting.
One important point is controlling glare. Direct sunlight penetration in classrooms and office
spaces often produces an unpleasant glare on work surfaces, making it difficult to work or
view a computer screen.
The proper orientation of windows and skylights can admit direct and diffused daylight,
producing the best combination of light for a building while also reducing glare. The
selection and placement of windows and skylights should be determined by the amount of
light needed and be based upon climate and the design of the building.
Day lighting also calls for controlling the amount of heat that enters a building. Because the
sun is such a powerful source to light buildings, it can also produce tremendous amounts of
heat. If not planned properly, using natural lighting can result in undesirable heat gains.
It may seem that it would be difficult to increase the amount of light without bringing in extra

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heat. However, the use of window treatments, window films and glazing can shade a window
or diffuse direct sunlight, minimizing heat gain. This can reduce overall cooling loads,
eliminating the need for a larger cooling system, resulting in additional overall savings.
Too much heat or light are not the only challenges associated with day lighting strategies.
Some architectural features, such as a building’s roof, atrium shapes or a building’s angles,
can prevent daylight from illuminating a space. To prevent daylight obstruction, wall
openings should be strategically placed within the space.
For example, if elements that can block daylight are located high up in the space they should
be as far from wall openings as possible. In a plan that features both open and enclosed
spaces, open space areas should be close to the wall openings. This maximizes the effect of
daylight, reflecting light deeper into the space. (source : Daylighting: Overcoming Glare and
Heat Challenges by Mike Molinski &Daylighting Benefits by Mike Molinski )
2.6 STRATEGIES AND ELEMENTS
Obviously there are many ways to allow natural light into the spaces within a building.
However as a generalisation, day lighting systems can be categorised into five main types, as
outlined in the sections below. Each type should be seen as having two parts, an aperture to
collect the daylight, and a distribution system to control or direct the light within the space.
Windows
Vertical windows are the most commonly used type of day lighting system. Many rooms
have windows only on one side, however light levels fall off quite quickly as you move
deeper into the space.
Figure 3 : - Cross section shows lighting distribution from a single-sided window
installation.
As a general rule of thumb, useful day lighting will only reach a distance of 2.5 times the
height of the top of the window above the work plane (usually taken at a desk height of

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600mm). In a standard office building with a window height of 2.5m, this means a maximum
of about 5-7metres.
Figure 4 : Day light penetration
Figure 2 - A general rule-of-thumb is that, for a vertical window, useful daylight penetration
is up to a depth equal to 2.5 times the height of the effective window head above the
horizontal surface of interest.
This can be overcome to some extent by adding windows on multiple sides of the room or by
using distribution systems such as a light shelf or prismatic glazing to direct some of the light
up onto the ceiling where it will diffuse deeper into the space.
Figure 5 : Lighting distribution with windows on two sides
Figure 6 : light shelves
Lighting distribution with windows on two sides or with a reflective lightshelf on only one
side.
There are two important issues to remember with side lit rooms. The first is that, under worst-
case overcast sky conditions, the daylight from the sky near the horizon is only around one
third that of the zenith. Thus, long thin horizontal windows will not provide as much light per
unit area as taller more vertical windows. However, taller windows require more solar control
to prevent direct sun penetration. The second issue is that the overall directionality of light

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entering the space will be more horizontal the deeper you go into the space, making shadows
longer and decreasing contrast.
Figure 7 : Cross section showing how illumination vectors become more horizontal as
sidelight travels deeper into a space.
Figure 4 - Cross section showing how illumination vectors become more horizontal as
sidelight travels deeper into a space. (Image source: whole building design guide –
www.wbdg.com)
2.6.1 Skylights
Skylights are apertures cut through the roof of a building. Whilst skylights give excellent
daylight levels, it is difficult to control the direct beam solar radiation from the Sun when it is
directly overhead. Angled louvers or some other form of seasonally adjustable shading must
therefore be used, especially in hot climates.
Figure 8 : Effect of skylight on Day light distribution
Given their location in the roof, skylights tend to gain and lose heat by convection and
conduction more than other types of windows. Avoid vented units as these can cause
draughts. Double-glazed units should be used wherever possible to reduce conducted heat
losses. There are a range of louvered systems available that can provide summer protection
from sunlight whilst still allowing the majority of daylight in winter.
2.6.2 Saw-tooth Skylights / North lights
Saw-tooth apertures are a top-lighting technique formed from a vertical glass element and a
sloping roof. The light distribution element can be light-coloured baffles or the sloping
ceiling itself. A window in an equator-facing saw-tooth needs to be shaded in the same way

20
as any other equator-facing window, usually by extending the sloped roof to provide an
overhang to protect against direct sun penetration.
Figure 9 : Day light distribution due to a saw tooth roof lighting system
Figure 6 - The daylight distribution due to a saw-tooth roof-lighting system.
Saw-tooth glazing that faces away from the equator will provide diffuse daylight from the sky
without any direct sun penetration so do not require any horizontal shading - though you
should still be careful to consider low altitude Sun at sunrise and sunset times in Summer.
Saw-tooth glazing that faces East or West is much more difficult to protect as every day the
Sun rises and sets at a low angle, resulting in direct penetration. Unless you can adequately
protect against this, they should be avoided. Where possible use double-glazed windows and
ensure they are properly sealed to prevent heat loss through infiltration and exfiltration.
2.6.3 Roof Monitor
A monitor aperture is similar to the saw-tooth roof but has two opposing vertical glazed
elements raised above the general roof line. The distribution system too can be light-coloured
baffles or the ceiling of the monitor.
Figure 10 : Day lighting distribution due to a raised roof monitor

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2.6.4 Atrium
The atrium, or light well, is a core lighting technique used in many modern multi-storey
buildings. The centre of the building is opened up with a glazed element at the top. The
outside perimeter is lit with windows whilst the centre receives diffuse light from the atrium.
Figure 12
The ratio of height to width of the light well should not be greater than 2:1 in most
circumstances. If this ratio cannot be achieved, then it is also possible to use reflectors or
diffusers suspended within the atrium space to bounce light sideways and therefore deeper
into adjacent internal spaces.
A central atrium is not the only way of providing a light well - it is also possible to 'duct'
daylight deep into a space. If the sides of such light wells are coated with highly reflective
materials they can be a very efficient day lighting solution where side windows are not
possible. Figure 9 below demonstrates how the addition of light wells down each side of the
atrium building used in Figure 8 can significantly increase the overall lighting level and
provide usually inaccessible spaces with a sense of connection with the outside.
Figure 9 - An example of the use of highly reflective ducted light wells to direct light deep
into usually inaccessible spaces. (Image source: whole building design guide –
www.wbdg.com)
Figure 11

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2.7 CASE STUDY: Le Corbusier’s Chapel at Ronchamp
The chapel of Notre Dame du Haut, designed by Le Corbusier, is located in Ronchamp. The
Chapelle Notre-Dame-du-Haut, a shrine for the Catholic Church at Ronchamp was built for a
reformist Church looking to continue its relevancy. Warning against decadence, reformers
within the Church looked to renew its spirit by embracing modern art and architecture as
representative concepts. Father Couturier, who would also sponsor Le Corbusier for the La
Tourette commission, steered the unorthodox project to completion in 1954.
This work, like several others in Le Corbusier’s late oeuvre, departs from his principles of
standardization and the machine aesthetic outlined in Vers une architecture. It is interesting
to note though, that even in this project, the structural design of the roof was inspired by the
engineering of airfoils.
The chapel is clearly a site-specific response. By Le Corbusier’s own admission, it was the
site that provided an irresistible genius loci for the response, with the horizon visible on all
four sides of the hill and its historical legacy for centuries as a place of worship.
Figure 13 Interior of Notre Dame du haut (looking up)
This historical legacy weaved in different layers into the terrain — from the Romans and sun-
worshippers before them, to a cult of the Virgin in the Middle Ages, right through to the
modern church and the fight against the German occupation. Le Corbusier also sensed a
sacral relationship of the hill with its surroundings, the Jura mountains in the distance and the
hill itself, dominating the landscape.
The nature of the site would result in an architectural ensemble that has many similitude’s
with the Acropolis, starting from the ascent at the bottom of the hill to architectural and

23
landscape events along the way, before finally terminating at the sanctum sanctorum itself,
the chapel.
The building itself is a comparatively small structure enclosed by thick walls, with the
upturned roof supported on columns embedded within the walls. In the interior, the spaces
left between the wall and roof, as well as asymmetric light from the wall openings serve to
further reinforce the sacral nature of the space and buttress the relationship of the building
with its surroundings.
Image
Image

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2.8 CASE STUDY : LAURIE BAKER’S CENTER FOR DEVELOPMENT
STUDIES – TRIVANDRUM , KERALA, INDIA
2.8.1 Main features of this building:
• He designed the buildings at the Centre to practically cool them.
• He renders jalis, a perforated wooden screen found in traditional Indian architecture, in
brick;
• The open grillwork allows cool breezes to waft into the interior while filtering harsh,
direct sunlight.
• Some buildings include a series of small courtyards containing shallow pools in the
centre, whose evaporation helps cool the air.
• Paying close attention to the existing site as he began to design the project, Baker left
as many coconut palm trees in place as possible to cast cooling shade onto the campus.
• The Computer centre at the Centre for Development Studies, Thiruvananthapuram.
Here Baker evolved an innovative system of curved double walls to save on cost and to
conserve the energy .
• In evaluating the campus for the Centre, Baker planned roads along the lower, while
footpaths were routed along naturally occurring elevated areas; following the natural
topography helps to limit erosion and despoilment of the environment.
• Brick walls were left un plastered and brick corbelling was used rather than more
expensive concrete lintels.
• With his mastery over his medium, Baker creates a variety of textures and patterns by
simple manipulation of the way in which bricks are placed in the wall.
• The architecture of this academic complex was conceived as a demonstration of
economically responsible building practices.

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Figure 14 : Center for development
studies

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2.9 CASE STUDY: TADAO ANDO ‘S CHURCH OF LIGHT, IBARAKI,
OSAKA, JAPAN
The Church of the Light is a small structure on the corner of two streets at Ibaraki, a
residential neighbourhood. It is located 25 km north-northeast of Osaka in the western
foothills of the Yodo valley railway corridor. The church has an area of roughly 113 m²
(1216 ft²): about the same size as a small house.
The church was planned as an add-on to the wooden chapel and minister's house that already
existed at the site. The Church of the Light consists of three 5.9m concrete cubes (5.9m wide
x 17.7m long x 5.9m high) penetrated by a wall angled at 15°, dividing the cube into the
chapel and the entrance area. One indirectly enters the church by slipping between the two
volumes, one that contains the Sunday school and the other that contains the worship hall.
The benches, along with the floor boards, are made of re-purposed scaffolding used in the
construction. A cruciform is cut into the concrete behind the altar, and lit during the morning
(as it is facing east).
Figure 15 : Church of light, Ibaraki, Osaka, Japan. Architect: Tadao Ando

27
It took more than two years to complete. The delay in completing the work was due to
problems in raising the necessary funds. Initially it was feared that it would cost more than
the budget and Ando even considered building it without a roof, but the construction firm
donated the roof and this became unnecessary.
Tadao Ando often uses Zen philosophies when conceptualizing his structures. One theme he
expresses in this work is the dual nature of existence. The space of the chapel is defined by
light, the strong contrast between light and solid. In the chapel light enters from behind the
altar from a cross cut in the concrete wall that extends vertically from floor to ceiling and
horizontally from wall to wall, aligning perfectly with the joints in the concrete. At this
intersection of light and solid the occupant is meant to become aware of the deep division
between the spiritual and the secular within him or herself.
One feature of the interior is its profound emptiness. Many
who enter the church say they find it disturbing. The
distinct void space and absolute quiet amounts to a sense
of serenity. For Ando the idea of 'emptiness' means
something different. It is meant to transfer someone into
the realm of the spiritual. The emptiness is meant to
invade the occupant so there is room for the 'spiritual' to
fill them.
The one element carried through Tadao Ando's structures is his idolization of the reinforced
concrete wall. The importance given to walls is a distinct departure from Modernist
architecture. They are usually made of 'in-situ' poured in place concrete. Considerable care is
taken to see that the walls are as perfect as technique will allow. These walls are thick, solid,
massive, and permanent. The main reinforced concrete shell of the Church of the Light is 15
inches thick.
"In all my works, light is an important controlling factor," says Ando. "I create enclosed
spaces mainly by means of thick concrete walls. The primary reason is to create a place for
the individual, a zone for oneself within society. When the external factors of a city's
environment require the wall to be without openings, the interior must be especially full and
satisfying." And further on the subject of walls, Ando writes, "At times walls manifest a
power that borders on the violent. They have the power to divide space, transfigure place,
Figure 16 : Church of light

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and create new domains. Walls are the most basic elements of
architecture, but they can also be the most enriching."
A smooth surface was achieved by adopting a dense
engineering quality mix with a slump less than 15cm (6in)
and by ensuring thorough vibration with a minimum cover for
the reinforcing bars of 5cm (2in) to avoid weathering
problems and staining. The density of the concrete results in a
glass-like surface that registers the different qualities of light,
and tends to dematerialize it. Because Ando's concrete is so
precisely wrought, so smooth and reflective, it produces an
illusion of a taut, textile surface rather than presenting it as a
heavy earthbound mass. Ando has his own teams of expert carpenters to make the formwork
who compete against each other; even so, his walls contain imperfections and are uneven."
("Church on the Water, Church of the Light" by Tadao Ando and Philip Drew)
(http://ibaraki-kasugaoka-church.jp/index.html)
(http://en.wikipedia.org/wiki/Church_of_the_Light)
Figure 17 : church of light
– from the dark

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2.10 FENESTRATION - THE IMPORTANCE OF WINDOWS
No one can deny the historical importance of daylight in determining the form of buildings
since, together with the effects of climate and location, daylight availability was fundamental
to their design. However, with the introduction of modern sources of electric light, and
particularly because of their increasing efficiency since the Second World War, by the 1960s
the need to introduce daylight into buildings had appeared to diminish.
A number of architectural programmes such as offices, shopping centres, factories, sports
buildings and even schools were developed as ‘blind’ or ‘semi-blind’ boxes on the
assumption that other environmental factors such as heating, cooling and acoustics would be
better served if there were no windows – the best window was no window. This assumption
was engineering biased, where all the less tangible advantages of daylight entry to a building
could be ignored. It was never a sound argument and is even less so today. The introduction
of daylight with all its variety has always been recognized by architects as having
positive advantages, and now this view has gained ground due to the realization that our finite
resources of energy must be conserved in world terms. The developed nations need to
consider how savings of energy through building design can make a positive
contribution.(Lighting modern buildings,Derek Phillips)
2.11 GLASS – AN INTEGRAL PART OF WINDOW
Glass is the dominating material in modern day architecture which places optical emphases
and provides for numerous technical functions. Today, the glass industry offers glazing with
individual technical features that can be used for heat, solar, or sound protection, as design
components, safety glass, or as a part of solar systems. The main focus in building is usually
on saving energy, especially in these challenging times of increasing prices for energy and
raw materials. The strong differentiation between the technical functions in turn makes
individual consultation even more important.
Glass is no longer just a filler element, but is rather nowadays also used for supporting or
enveloping purposes. A closer examination of this multifunctional building material requires
a look at its historical background and also at the fast developments of modern times.
( http://www.nbmcw.com)
"At the beginning, the desire is to design, not the respective function. The function "slips in"
(Professor Klaus Pracht, architect and author in Bad Muender am Deister.)

30
Apart from the primary purpose of a window, more and more additional features, mostly
application and structural solutions, have been demanded. As a result, we now speak of
functional glazing and facades. Primary use (inter alia)
 Supply of natural daylight
 Protection from rain, wind, and cold
 Transparency or translucency
 Means of communication
 Supply of fresh air
 Secondary use (inter alia)
 Heat protection
 Sound protection
 Solar protection
 Object and personal protection
 Fire protection
 Temporary heat and solar protection
 Use of solar energy
 Living comfort
 Means of design
 Electromagnetic dampening.
These purposes, which are characteristic for windows, can be achieved by means of special
multifunctional designs. Sophisticated window and facade systems combine technical
demands with the creative freedom of planning. Such systems are a challenge for architects
and manufacturers. With the increasing demands of window and facade systems, the demands
of glazing also increase in terms of quality and versatility. Most requirements concern
increased protection, which can only be achieved with modern functional insulation glazing.
As against traditional buildings, glazed buildings or those with huge glass facades offer more
amount of daylight within the premises. While it provides increased light within premises, it
also saves on electricity bills. Translucent glass channels like Pilkington Profilit allow
daylight to come in the building even as they retain privacy.

31
Studies indicate that patients who have better access to daylight and natural surroundings
often recuperate faster than those who do not. So, in that aspect too switching over to glass
makes sense.
2.11.1 ENERGY EFFICIENT GLAZING
Glazing is not to be left behind in the world-wide quest for sustainable living. Windows,
which are normally thermal holes and in an average home cause 30% loss of heat or air-
conditioning energy, are being replaced by energy efficient options. Energy-efficient
windows save money every month. The payback period for selecting energy-efficient units
ranges from two years to ten years. In new construction, their higher initial cost can be offset
because you’ll probably need a smaller, less expensive heating and cooling system. More
durable windows may cost less in the long haul because of lowered maintenance and
replacement cost.
2.12 APPLICATIONS OF DAY LIGHTING STRATEGIES
2.12.1 BUILDING DESIGN
Daylight strategies should try to bring light into the core of the building to reduce energy
consumption and to profit from the benefit of daylight, which is usually more appreciated
than artificial lighting.
Architects can create apertures through the envelope of the building (lateral or zenithal
apertures). But they can also work with sun ducts, patio, atria, etc., to introduce light in the
core of the building. Whatever the device envisaged to bring light deep into the building,
there are some general principles which strongly influence the luminous distribution, levels
of illuminance and the luminous environment of a room.
The type of glazing and its luminous transmission will have an influence on the quantity of
light penetrating the room. Width of window frame will also have an influence on the
quantity of light penetrating the space, and on the risk of glare due to the contrast between the
window and the wall.

32
When designing a building it is interesting to create luminous atmospheres, visually
interesting and adapted to the activity taking place in the space. It will be necessary to
comprehend light from a quantitative and a qualitative point of view.
2.12.2 INFLUENCE OF THE SIZE OF THE APERTURES
The size of the glazed surface has a large influence on the quantity of daylight in the room.
Average illuminance increases with the glazed surface.
Influence of the location of the aperture
The location of the window, and especially its height, has an influence on the luminous
distribution in a room. When the aperture is high, illuminance in the bottom of the room is
higher. Moreover, illuminance distribution changes according to the height of the lintel: when
the aperture is high, there is a shaded zone near the window which increases when the lintel
location rises.
2.12.3 INFLUENCE OF SIZE AND GEOMETRY OF APERTURE
Illuminance in the room for three windows of identical area, but with different proportions
will be compared.
When the width of the window decreases, illuminance distribution is less uniform but average
illuminance is practically the same. Illuminance in the bottom of the room increases with the
height of the window. So, for an identically galzed surface, a higher window will be
potentially more effective. The ideal lies thus in a horizontal window whose lintel is high. To
a first approximation, a room will be suitably enlightened until a depth of 2 to 2.5 times the
height of the lintel
2.12.4 INFLUENCE OF WINDOW FRAME
The window frame modifies the quantity of light penetrating in the building as it reduces the
aperture in the wall. A fixed window frame is thinner than a mobile one but it is often
necessary to plan opening windows for ventilation, maintenance and general comfort of the
occupant (contact with outside). The material chosen for the frame has also an influence on
its size. A window frame in wood will be thinner than in PVC. Moreover, the choice of its
colour will have an influence on the visual contrast, mainly from inside of the room.

33
2.12.5 INFLUENCE OF LUMINOUS TRANSMITTANCE
Luminous transmittance (LT) of a glazing is the percentage of light transmitted through this
glazing. The type of glazing (simple, double, reflective, heat-absorbing, low emissivity, etc.)
directly affects its transmittance. A balance has to be made between the quantity of light
entering the building, the minimisation of heat loss and maximisation or minimisation of
solar gains, depending on the building type and the climate. For that reason, solar factor (g),
thermal conductivity coefficient (U) and luminous transmission (LT) will be analysed in
parallel.
2.12.6 INFLUENCE OF SLOPE OF APERTURE
The slope of the glazing has a large influence on the quantity of direct solar radiation which
enters into a room. This graph shows the variation of luminous transmittance for a clean
glazing according to the angle of incidence of the solar rays. When the luminous rays strike
the glazed surface according to an angle lower than 40° compared to its normal, the reduction
in the luminous transmission of the glazing is negligible, but it increases very quickly when
the angle of incidence of the solar radiation exceeds 60°.
2.12.7 INFLUENCE OF GLAZING CLEANLINESS
Luminous transmittance of a glazing will depend strongly on the cleanliness of the glass.
2.12.8 INFLUENCE OF DIMENSION OF THE ROOM
Light will be distributed differently according to the shape of the room. Corners in a room
will create shadoed zones while light will slide on the wall of a round room.
Illuminance level and distribution vary also according to the dimensions of the room. For an
identical floor to glazing area ratio, illuminance levels in the room will increase when the
width of the room increases.
Diffuse light penetrates significantly until about two times the height of the window lintel.
Illuminance levels decrease at the back of the room. It is thus necessary to reduce the depth of
the room to increase naturally lit surfaces.

34
2.12.9 INFLUENCE OF ARRANGEMENT OF FURNITURE
Furniture can become an obstacle for the penetration and the distribution of light in the room.
Thus, it will be necessary to place them in the room taking into account the windows
position. Their colour and their material will also have an influence on the reflection of light
in the room.
2.12.10 INFLUENCE OF COLOUR & COEFFICIENTS OF REFLECTION OF THE
ROOM
The ability of materials to reflect light depends on their texture and colour. It influences the
illuminance levels in the room and the luminance distribution. The higher the reflectance of
indoor materials, the more luminous a room may seem. Light will be well distributed in the
room if surfaces are clear. Moreover, human eye analyses luminance, and a clear surface will
be perceived as brighter than a dark surface, even under the same illuminance level.
Generally, coefficients of reflection of surfaces near windows have a predominant role in
internal reflections. The colour of the ceiling has a minor influence on the reflection of light,
as it receives only reflected light. On the other hand, the floor and the other horizontal
surfaces in the room have a high influence on the reflection of light, as they are the most
exposed surfaces to direct and diffuse light.
Consequently, to favour the depth distribution of light in a room, it is recommended to work
with clear floor and relatively clear furniture, thus having a high reflectance. Moreover, the
clearness of the work tables will be favourable to visual comfort as it reduces contrast
between a sheet of paper and the counter. However,
for a matter of cleaning, grounds are often relatively of
dark colours. It will thus be necessary to find a
compromise to meet illuminance requirements.
2.13 ALTERNATE GLAZING
MATERIALS
Different types of glazing materials have come to the
fore as more and more architects and designers realize
the need to install energy efficient materials. No one
type of glazing satisfies all applications. Many
Figure 18 : Alternate glazing material

35
alternate materials like polycarbonate (PC), polyethylene (PE), acrylic, fiberglass, and PVC
are available that serve different purposes. Moreover, clients may feel the need to use two
types of glazing for a home because of the directions of the windows and the local climate.
Let us look at these materials separately and find out their properties.
2.13.1Polycarbonate (PC):
Of the entire glazing materials available today, clear, high-impact resistant polycarbonate
material offers the widest range of properties. The advantages of PC are its clarity, safety,
security, energy savings and the designing freedom, it offers to the architects. It is available
in various sizes and configurations, the most important ones being single layer and multi-
layer sheets.
2.13.2 Advantages:
Polycarbonate is one of the toughest carbonate sheet available, about 300 times stronger than
the glass. These can be joined mechanically, solvent bonded and welded. PC also has
excellent resistance to dilute acids and mineral oils and fairly good resistance towards alcohol
and vegetable oils. The life expectancy is about 10 years and they have a maximum working
temperature of 250 degrees F. The PC sheets are about half the weight of comparative glass
products and are mainly used for flat glazing applications that require high abrasion and
impact resistance.
2.13.3Properties:
It is lightweight and easy to work with. Typical light transmission (PAR) is 79% for double
wall and 87% for single wall. However, recent advances have produced polycarbonates with
light transmission properties equal to or even exceeding glass. Polycarbonate also comes in
twinwall or even triplewall sheets in thicknesses from 4 to 16mm and is easy to cut. Twinwall
PC has an R-value of about 1.4, and triplewall PC has an R-value of 2.5. PC has a high
degree of light transmittance and low thermal IR transmittance. Light is diffused with PC,
lowering the risk of foliage burn.

36
2.13.4 Applications:
Polycarbonate is mostly used for window glazing, greenhouse glazing, space shuttle
windows, astronaut visors and industrial eye protection. It is available in various colors like
clear, opal, grey and bronze. Besides its application as an alternate to glass for glazing, PC
also finds applications in store fonts, signage, display cases, newspaper type racks and
security barriers.
2.13.5 Acrylic:
today, is not as common as it used to be but it’s still available as a single- or double-walled
material. It brings many advantages as an alternative to glass. Acrylic s0heet is made up of
thermoplastics and has very good weather resistance. It is five times stronger than glass but
can easily be scratched. Acrylic is relatively easy to bend around large-diameter curves and
has a lifespan from 10 to 30 years.
2.13.6 Advantages:
It offers excellent optics, is light in weight and it’s easy to fabricate. It resists breaking and
inherently has a higher level of U.V. protection. Acrylic has a light penetration of 92% for
sheets 30 mm thick. It can be easily heat-formed without losing its clarity.
2.13.7 Properties:
Acrylic has good resistance to many chemicals,
including salt spray or corrosive atmospheres but is
attacked by aromatic and chlorinated hydrocarbons,
esters, ketones and ethers. The Acrylic sheet
thicknesses range from 1/16 to 4 in and the sheet
image sizes are produced up to 120 in. x 144 in. The only
disadvantage with Acrylic glazing materials is that being softer than glass, they are more
prone to scratch easily, can accumulate static, and get dustier faster than glass.

37
It is used for glazing in industrial plants, schools and other institutional buildings where there
is a high breakage rate and also in workshops, glasshouses, outhouses, playhouses. It is also
used for windows and window replacement glass. Besides the colorless transparent sheet,
acrylic is also produced in a great variety of transparent, translucent and opaque colors and in
a variety of surface patterns.
2.14.9 Perspex:
This is the brand name for acrylic sheet produced only by Lucite International and
chemically known as polymethyl methacrylate (PMMA) acrylic sheet which is manufactured
from methyl methacrylate monomer (MMA). It was first used for aircraft canopies and then
for a wide variety of architectural and industrial applications. It is one of the hardest
thermoplastics and remains aesthetically attractive for much longer than many other plastic
sheet products. It is five times stronger than float glass and internationally, it meets the
glazing material requirement of ANSI Z.97 and BS 6262. The life span of Perspex is 10
years.
2.14.10 Advantages:
Clear Perspex transmits 92% of all the visible light. It is one of the hardest thermoplastics
and remains aesthetically attractive for a longer duration. It has a maximum service
temperature of 80-85°C with minimum risk of thermal distortion.
2.14.11 Properties:
Perspex is light and non-breakable, abrasion–resistant and is easy to thermoform thus
ensuring cost effective production. It has a high gloss surface, making it easy to clean,
thereby guaranteeing low maintenance costs. It is fully recyclable and is rated Class C to BS
6206 impact test and Class A for 8 mm and above thicknesses. There are three forms of
Perspex available, Cast, Extruded and Impact Modified Perspex.

38
Perspex mainly finds use in outdoors, like conservatory roofs and shed windows, kitchen and
bathroom splash backs. Perspex comes in about 55 colors which include natural shades, opals
and tints. Perspex also comes in exciting effects such as gloss, silk, matt, frosted, fluorescent
& live edge, and pearlescent as well as a diamond surface texture.
2.15 FUTURE OF ALTERNATE GLAZING MATERIAL
With many more alternate glazing materials already in the category, researchers are still busy
developing new kind of windows called “smart windows” or Chromogenic or optical
switching windows which will enable windows to adjust their transmittance vis-à-vis the
temperature (thermochromic) or light (photochromic) fluctuations or in response to small
electrical currents (electrochromic). With a host of options available for glazing besides glass,
the future definitely looks brighter and lighter!

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CHAPTER III : METHODOLOGY
3.0 CALCULATIONS AND THUMB RULES
One of the aims of day lighting design is to provide enough daylight in a room to realize
several tasks and to create a luminous comfortable space.
There are different ways to predetermine daylight availability in a building. It can be done
with simplified models (tables, diagrams, etc.), complex models (computer tools, etc.), and
scale models (under real sky or artificial sky).
To quantify daylight in a space, you can choose to work with static or dynamic metrics.
The most familiar static metric is the daylight factor. Daylight factor (DF) expresses the ratio
between illuminance on the work plane and illuminance available outdoor, under an overcast
sky. It is easily calculated (scale model under artificial sky, split flux method, computer tools,
etc.). But is based on the worst sky conditions: the overcast luminance distribution. That is
why it is necessary to couple illuminance information obtained from the calculation of DF,
with the penetration of sun in the room and with risks of glare, which change over the year.
Some dynamic metrics, called climate-based daylight metrics (CBDM), were developed
recently to counter the limitations of daylight factor and take into account some important
parameters (evolution of availability of light over the year, orientation of the building and
penetration of sun, location of the building, etc.). These dynamic metrics will give
information about the ability of the designed room to reach a minimum level of illuminance
with only daylight, like the daylight autonomy (DA). Or the ability of the room to reach an
illuminance goal, like the useful daylight index (UDI) and the illuminance metric developed
in Light solve.
3.1 Daylight factor (DF)
The daylight factor is the ratio of the interior natural illuminance received at a point of a
reference plane with the simultaneous external illuminance of a horizontal surface in a
perfectly unobstructed site under overcast sky.

40
These two illuminance values are due to the light received from a same sky, whose
distribution of luminance is estimated or is known, with direct sunlight being excluded. The
daylight factor is expressed as a %.
DF = 100 * Einterior / Eexterior (%)
Under overcast sky conditions, daylight factor values are independent of the orientation of
glass windows, of the season and of the time of day. In this way, they give an objective and
easily comparable measurement of illumination quality inside a building. A room's daylight
factor values can then be compared with the values of the minimum daylight factor reference
values.
However, the daylight factor (DLF) does not make it possible to immediately see whether the
recommended illuminance levels for a visual task have been reached.
Daylight factor presents some limitations:
 It does not take into account the location of the studied room in terms of climate (eg,
there's no consideration for how which percentage of the year really presents an
overcast sky).
 It does not take into account the location of the studied room in terms of latitude
(what is the course of the sun? is there some sun penetration in the building?)
 It gives no information about risk of glare.
 It gives no information about quality of light.
Daylight factor should be considered as an indicator of the minimum level of illuminance
reached under an unfavourable sky. It should be completed by maximal illuminances reached
under sunny sky.
If the architect does not verify sun penetration, illuminance under more favorable sky and
risks of glare, a design resulting from the only consideration of DF can suggest buildings with
too much glazing which lead to overheating and risks of glare.
Nevertheless, calculation of DF is nowadays the basis of daylighting design in the French
HQE standard (High environmental quality) and in LEED.

41
3.2 Climate-based daylight metrics (CBDM)
Climate-based daylight metrics (CBDM) are dynamic metrics calculated on the basis of
weather data files. Contrary to static metric, dynamic illuminance, luminance and glare
metrics evolve over the year according to the outdoor daylight availability. The amount of
data simulated for the whole year is quite large and should be reduced with the development
of CBDM.
Evaluation of CBDM can be realized through dynamic computer simulations or measurement
in scale models. For each point in the space and for each moment (generally one hour)
illuminance, luminance or glare can be calculated. Some CBDM suggest a spatial analysis
while some others a temporal analysis.
Dynamic autonomy (DA) at a point of interest is the percentage of yearly occupied time for
which a certain light level is reached through the use of daylight only. All sky conditions are
considered through weather data files. Dynamic autonomy can be easily calculated for an
area of interest with DAYSIM software. DA gives a spatial information. (DA is developed by
C. Reinhart) .
Useful Daylight Illuminance (UDI) is a goal-oriented metric which informs about how fixed
satisfying illuminance are spatially reached. UDI is the annual occurrence of illuminance, at a
point, which are within the useful fixed range of illuminance. Illuminance metric developed
in Lightsolve is, like the UDI, a goal-oriented metric. It fixes a rage of target values and
evaluates the percentage of space whose performances falls within the range. So, contrary to
UDI which evaluates the percentage of time for which fixed illuminances are reached on the
workplane, in Lightsolve, it is the percentage of space satisfying criteria which is evaluated
over the year.
Satisfying illuminance range is fixed as well as minimum and maximum acceptable
illuminance. Partial credits are given if satisfying range illuminance is not reached but that
tolerable illuminances (minimum or maximum) are not exceeded.( www.energies-
renouvelables.org Images source: Architecture et Climat, Research Group, Université
Catholique de Louvain. Available at: http://www-climat.arch.ucl.ac.be/)

42
3.3ECOFRIENDLY LIGHTING – ARTIFICIAL LIGHTING
3.3.1 CFL LIGHTS (compact fluorescent lights)
A compact fluorescent lamp (CFL), also called compact fluorescent light, energy-saving
light, and compact fluorescent tube, is a fluorescent lamp designed to replace an incandescent
lamp; some types fit into light fixtures formerly used for incandescent lamps. The lamps use a
tube which is curved or folded to fit into the space of an incandescent bulb, and a compact
electronic ballast in the base of the lamp.
Compared to general-service incandescent lamps giving the same amount of visible light,
CFLs use one-fifth to one-third the electric power, and last eight to fifteen times longer. A
CFL has a higher purchase price than an incandescent lamp, but can save over five times its
purchase price in electricity costs over the lamp's lifetime. Like all fluorescent lamps, CFLs
contain mercury, which complicates their disposal. In many countries, governments have
established recycling schemes for CFLs and glass generally.(www.en.wikipedia.org)
CFLs radiate a spectral power distribution that is different from that of incandescent lamps.
Improved phosphor formulations have improved the perceived colour of the light emitted by
CFLs, such that some sources rate the best "soft white" CFLs as subjectively similar in colour
to standard incandescent lamps.
To make sure you get the same amount of light when replacing standard bulbs with compact
fluorescent light bulbs, check the lumen rating on the light you are replacing and purchase a
compact fluorescent light bulb with the same lumen rating. (A lumen rating is the measure of
light the bulb puts out.)
Wattage varies greatly between standard light bulbs and compact fluorescent light bulbs.
Compact fluorescent light bulbs typically use about one-quarter of the wattage used by
standard bulbs to produce the same amount of light. So to replace a traditional 60-watt bulb,
look for a compact fluorescent light bulb that is about 15 watts.
Compact fluorescent light bulbs are available in many different sizes and shapes to fit in
almost any fixture—from three-way lamps to dimmer switches—for both indoor and outdoor
use. Compact fluorescent light bulbs also come in a variety of color temperatures, which

43
helps determine the color and brightness of the light each bulb provides.
(http://environment.about.com/od/greenlivingdesign/a/light_bulbs.htm)
3.3.2 LED LIGHTS (Light emitting diode)
An LED lamp (or LED light bulb) is a solid-state lamp that uses light-emitting diodes (LEDs)
as the source of light. LED lamps offer long service life and high energy efficiency, but initial
costs are higher than those of fluorescent and incandescent lamps. Chemical decomposition
of LED chips reduces luminous flux over life cycle as with conventional lamps.
Commercial LED lighting products use semiconductor light-emitting diodes. Research into
organic LEDs (OLED), or polymer light-emitting diodes (PLED) is aimed at reducing the
production cost of lighting products. Diode technology currently improves at an exponential
rate.
LED lamps can be made interchangeable with other types of lamps. Assemblies of high
power light-emitting diodes can be used to replace incandescent or fluorescent lamps. Some
LED lamps are made with bases directly interchangeable with those of incandescent bulbs.
Since the luminous efficacy (amount of visible light produced per unit of electrical power
input) varies widely between LED and incandescent lamps, lamps are usefully marked with
their lumen output to allow comparison with other types of lamps. LED lamps are sometimes
marked to show the watt rating of an incandescent lamp with approximately the same lumen
output, for consumer reference in purchasing a lamp that will provide a similar level of
illumination.
Efficacy of LED devices continues to improve, with some chips able to emit more than 100
lumens per watt. LEDs do not emit light in all directions, and their directional characteristics
affect the design of lamps. The efficacy of conversion from electric power to light is
generally higher than for incandescent lamps. Since the light output of many types of light-
emitting diodes is small compared to incandescent and compact fluorescent lamps, in most
applications multiple diodes are assembled.
Light-emitting diodes use direct current (DC) electrical power. To use them on AC power
they are operated with internal or external rectifier circuits that provide a regulated current
output at low voltage. LEDs are degraded or damaged by operating at high temperatures, so
LED lamps typically include heat dissipation elements such as heat sinks and cooling fins.

44
3.3.3 Size and Efficiency
LEDs measure from 3 to 8 mm long and can be used singly or as part of an array. The small
size and low profile of LEDs allow them to be used in spaces that are too small for other
lightbulbs. In addition, because LEDs give off light in a specific direction, they are more
efficient in application than incandescent and fluorescent bulbs, which waste energy by
emitting light in all directions. (See References 2)
3.3.4 Long Life
The life of a high-power white LED is projected to be from 35,000 to 50,000 hours,
compared to 750 to 2,000 hours for an incandescent bulb, 8,000 to 10,000 hours for a
compact fluorescent and 20,000 to 30,000 hours for a linear fluorescent bulb. LED lifetimes
are rated differently than conventional lights, which go out when the filament breaks. Typical
lifetime is defined as the average number of hours until light falls to 70 percent of initial
brightness, in lumens. LEDs typically just fade gradually. (See References 3)
3.3.5 Lower Temperatures
Conventional light bulbs waste most of their energy as heat. For example, an incandescent
bulb gives off 90 percent of its energy as heat, while a compact fluorescent bulb wastes 80
percent as heat (see References 4). LEDs remain cool. In addition, since they contain no glass
components, they are not vulnerable to vibration or breakage like conventional bulbs. LEDs
are thus better suited for use in areas like sports facilities and high-crime locations. (See
References 1)
3.3.6 nergy Star LEDs
Poorly designed LEDs may not be long-lasting or efficient. LEDs that are EnergyStar-
qualified should provide stable light output over their projected lifetime. The light should be
of excellent colour, with brightness at least as great as conventional light sources and
efficiency at least as great as fluorescent lighting. The LEDs should also light up instantly
when turned on, should not flicker when dimmed and should not consume any power when
turned off. (http://greenliving.nationalgeographic.com/advantages-benefits-led-lighting-
2139.html

45
3.4 ENERGY EFFICIENCY – NATURAL LIGHTING
3.4.1 SMART GLASS
In technological terms, the word “smart” or S.M.A.R.T. means Self-Monitoring Analysis and
Reporting Technology. Manufacturers of hard disk drives developed “smart” technology as a
way to increase hard drive reliability. The technology is what enables personal computers to
predict failures of hard disk drives. S.M.A.R.T. technology is not only an industry standard
for hard drive manufactures, but it is the industry standard for just about everything in today’s
world.
When smart technology comes to mind, most people think of smart phones. Smart phones
have the ability to do almost everything a desktop or laptop computer can do and sometimes
more. Owners can use their smart phone to surf the internet, pay bills, upload photos and
videos to photo sharing or social networking websites, and participate in video chatting.
Smart phones continue to advance in the many special features they provide their users and
the smart technology continues to be used in many other areas such as homes, schools,
businesses, and any other area in which smart technology can provide a number of benefits.
Windows made from SPD-SmartGlass enables end users to manually or automatically control
the amount of light, glare and heat passing through a window to create more comfortable and
environmentally friendly indoor spaces.
Using SPD-SmartGlass for your building’s windows can lead to a variety of practical
benefits, including being able to save money on air conditioning and heating as well as
eliminating the need to install and maintain motorized screens, blinds or curtains.
Another advantage of using this particular type of smart glass for your building’s windows is
that, unlike blinds, this smart glass product is capable of blocking harmful light while still
maintaining a clear view of the outside world. This increased the level of natural daylight,
which can improve health and well-being and therefore can have a strong influence on both
attitude and productivity in the workplace.
Many other supposedly smart glass products are permanently tinted to reduce glare. While
this might seem practical, it can lead to a situation where higher electricity costs are
generated to power more lights inside the building than is optimally needed. Windows made

46
from SPD-Smart Glass, however, are able to adapt to exterior lighting conditions in order to
create more comfortable indoor spaces and save electricity.
Smart glass windows manufactured by Smart Glass International are specially designed to
help reduce a building’s overall carbon emissions. All of these windows are made from
sheets of the highest quality, solid-state smart glass and have no movable parts to wear out or
break.
3.4.2 Strength
SPD Smart Glass windows are very strong and durable making them ideal for use in
overhead
glazing, children's rooms, sun rooms, conservatories, sports halls, swimming pools etc.
3.4.3 Noise protection
Protection much improved when compared with normal insulated glass units
3.4.4 Advantages of SPD Smartglass
 Instant and precise light control.
 Energy Savings on cooling & lighting costs.
 Eco friendly.
 Exceptional optical qualities that reduce glare and eye strain.
 Elimination of the need for expensive window dressings like electronic louvers;
blinds and shades used in architectural applications.
 High durability, solid state technology with no moving parts to wear out or break.
 Large sizes of any shape up to 2m * 1m can be produced.
 Stable colour characteristics for the life of the unit.
 Wide working temperature range from 30 to +90°C
 Ideal for exterior applications.
 Ambient temperature control.
 Aesthetically pleasing.
 Hygienic low maintenance material.
 Enhanced corporate and domestic image.
 Wide light transmission ranges.

47
 In an effort to reduce glare the windows of many commercial buildings are
permanently tinted, then requires more lighting inside the building than that which is
optimally needed. Residential homes using window experience a similar limitation.
Natural day lighting, which can be regulated using SPD Smart Glass™ products, has
been shown to improve health and well being, and thus its regulation is considered by
many to have a strong influence on one’s attitude and productivity. Reduces
uncomfortable “Gold fish bowl” feeling when living or working in high-density
buildings such as apartment blocks or office complexes.
 Reducing the fading of carpets, furniture and protect valuable artwork
 Protecting skin from damaging UV rays.
 High UV stability.
 Low working voltage.
 High contrast at any viewing angle and any illumination level.
 Long life tested to in excess of 100,000 cycles.
 Cost competitive.
 Infinite range of light transmission levels without the blocking of one’s view
3.4.5 Roof lights:
 Skylights.
 Roof lights
 Fixed or opening.
 Commercial / Domestic
(http://www.smartglassinternational.com/project-focus-the-brew-house-hotel/)
3.5 CASE STUDY : The Brew House Hotel, Kent, London
The Brew House Hotel is a luxurious boutique hotel, located close to the historic pantiles
area, at the heart of Royal Tunbridge Wells, Kent.
Smartglass were approached to deliver a room within a room in a form that would capture the
imagination while simultaneously maximising space and light.

48
Smartglass partitions provide a sleek and
minimalist façade through which en suites can be
revealed or concealed in an instant.Guests benefit
from privacy on demand without compromising
the luxurious sense of light and space in their
weekend retreat.
Besides are a sample of the reviews that guests
have submitted to the Trip Advisor website
concerning Privacy Smart glass in the rooms of
The Brew House Hotel.
3.6 FIBRE OPTIC CONCRETE WALL
Translucent Concrete is a combination of optical fibres and fine concrete. Thousands of fibres
run side by side transmitting light between the two surfaces of each element. Because of their
small size the fibres blend into concrete becoming a component of the material like small
pieces of ballast. In this manner, the result is not only having the two materials mixed - glass
in concrete - but a third, new material, which is homogeneous in its inner structure and on its
main surfaces as well.
In theory, a wall structure created out of Translucent Concrete blocks can be a couple of
meters thick as the fibres work almost without any loss in light up till 20 meters! Moreover,
the blocks are load-bearing and provide the same effect with both natural and artificial light.
Glass fibres lead light by points between the wall-surfaces. Shadows on the lighter side will
appear with sharp outlines on the darker one. Even the colours remain the same! Such a wall
with glass fibre-pixels acts as if scanner and screen are united. This special effect creates the
Figure 19 : smart glass application as a partition
Figure 20 : Smart glass turning out to be a normal
glass partition

49
general impression that thickness and weight of this concrete wall disappear.
(http://www.dezeen.com/2007/12/17/translucentconcrete-by-andreas-bittis/)
Translucent Concrete blocks are produced
depending on the aesthetical wishes and structural
needs of the architect’s project. Basically all sizes
of pre-cast concrete are possible: from small bricks,
to façade plates or passable paving stones, all
illuminated from beneath. Since the amount of
optical fibre is only 4%, Translucent Concrete
blocks have the same technical data as the concrete
used for them. The same flexibility occurs with the
fibres: Right now the diameter of the fibre can be
chosen from 2micro- to 2 millimetres. And also the
technique of making Translucent Concrete blocks
can differ according to the needs of the project:
from a slight "diffuse" aesthetic to a certain grid or
even a logo. Moreover Translucent Concrete is a
high density concrete – according to the extremely fine diameter of the fibres the other
aggregates need to be chosen carefully. Translucent Concrete elements are joined together
through splicing or agglutinating or in conjunction with any common framework. Talented
architects and engineers should feel challenged to create structures of extraordinary beauty
and innovation. Translucent Concrete is the first step to what might become the building
material of the future.
3.7TECHNOLOGIES
3.7.1 ACTIVE DAY LIGHTING
Active day lighting is a system of collecting sunlight using a mechanical device to increase
the efficiency of light collection for a given lighting purpose. Active daylighting systems are
different from passive day lighting systems in that passive systems are stationary and do not
actively follow or track the sun.
Figure 21 : Human standing behind a fibre
concrete wall. Image describes the translucent
nature of material

50
3.7.2 Types of active day lighting control systems
There are two types of active day lighting control systems: closed loop solar tracking, and
open loop solar tracking systems.
Closed loop systems track the sun by relying on a set of lens or sensors with a limited field of
view, directed at the sun, and are fully illuminated by sunlight at all times. As the sun moves,
it begins to shade one or more sensors, which the system detect and activates motors or
actuators to move the device back into a position where all sensors are once again equally
illuminated.
Open loop systems track the sun without physically following the sun via sensors (although
sensors may be used for calibration). These systems typically employ electronic logic which
controls device motors or actuators to follow the sun based on a mathematical formula. This
formula is typically a pre-programmed sun path chart, detailing where the sun will be at a
given latitude and at a given date and time for each day.
(http://en.wikipedia.org/wiki/Light_tube)
3.7.3 PASSIVE DAY LIGHTING
Passive day lighting is a system of both: collecting sunlight using static, non-moving, and
non-tracking systems such as Windows, Sliding glass doors, most skylights, light tubes, and
reflecting the collected daylight deeper inside with elements such as light shelves. Passive
day lighting systems are different from active day lighting systems in that active systems
track and/or follow the sun, and rely on mechanical mechanisms to do so.

51
3.8 HELIOSTATS
A heliostat (from Helios, the Greek word for sun, and stat, as in stationary) is a device that
includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward
a predetermined target, compensating for the sun's apparent motions in the sky. The target
may be a physical object, distant from the heliostat, or a direction in space. To do this, the
reflective surface of the mirror is kept perpendicular to the bisector of the angle between the
directions of the sun and the target as seen from the mirror. In almost every case, the target is
stationary relative to the heliostat, so the light is reflected in a fixed direction.
Nowadays, most heliostats are used for day lighting or for the production of concentrated
solar power, usually to generate electricity. They are also sometimes used in solar cooking. A
few are used experimentally, or to reflect motionless beams of sunlight into solar telescopes.
Before the availability of lasers and other electric lights, heliostats were widely used to
produce intense, stationary beams of light for scientific and other purposes.
Most modern heliostats are controlled by computers. The computer is given the latitude and
longitude of the heliostat's position on the earth and the time and date. From these, using
astronomical theory, it calculates the direction of the sun as seen from the mirror, e.g. its
compass bearing and angle of elevation. Then, given the direction of the target, the computer
calculates the direction of the required angle-bisector, and sends control signals to motors,
often stepper motors, so they turn the mirror to the correct alignment. This sequence of
operations is repeated frequently to keep the mirror properly oriented.
Large installations such as solar-thermal power stations include fields of heliostats
comprising many mirrors. Usually, all the mirrors in such a field are controlled by a single
computer.
There are older types of heliostat which do not use computers, including ones that are partly
or wholly operated by hand or by clockwork, or are controlled by light-sensors. These are
now quite rare. Heliostats should be distinguished from solar trackers or sun-trackers that
point directly at the sun in the sky. However, some older types of heliostat incorporate solar

52
trackers, together with additional components to bisect the sun-mirror-target angle.
(http://en.wikipedia.org/wiki/Heliostat)
Figure 22 : Heliostat with mirror on open space
Figure 23 : Cost reduction graph for heliostats & Titan trackers.

53
3.9 TUBULAR DAY LIGHTING DEVICES
Light tubes or light pipes are used for transporting or distributing natural or artificial light. In
their application to day lighting, they are also often called tubular daylighting devices, sun
pipes, sun scopes, or daylight pipes.
Generally speaking, a light pipe or light tube may refer to:
 a tube or pipe for transport of light to another location, minimizing the loss of light;
 a transparent tube or pipe for distribution of light over its length, either for
equidistribution along the entire or for controlled light leakage.
Both have the purpose of lighting, for example in architecture.
Figure 24 : Tubular day lighting devices
3.9.1 Solar and hybrid lighting systems
Solar light pipes, compared to conventional skylights and other windows, offer better heat
insulation properties and more flexibility for use in inner rooms, but less visual contact with
the external environment.
In the context of seasonal affective disorder, it may be worth consideration that an additional
installation of light tubes increases the amount of natural daily light exposure. It could thus

54
possibly contribute to residents´ or employees´ well-being while avoiding over-illumination
effects.
Compared to artificial lights, light tubes have the advantage of providing natural light and of
saving energy. The transmitted light varies over the day; should this not be desired, light
tubes can be combined with artificial light in a hybrid set-up. Some artificial light sources are
marketed which have a spectrum similar to that of sunlight, at least in the human visible
spectrum range, as well as low flicker. Their spectrum can be made to vary dynamically such
as to mimic the changes of natural light over the day. Manufacturers and vendors of such
light sources claim that their products can provide the same or similar health effects as
natural light. When considered as alternatives to solar light pipes, such products may have
lower installation costs but do consume energy during use; therefore they may well be more
wasteful in terms of overall energy resources and costs.
On a more practical note, light tubes do not require electric installations or insulation, and are
thus especially useful for indoor wet areas such as bathrooms and pools. From a more artistic
point of view, recent developments, especially those pertaining to transparent light tubes,
open new and interesting possibilities for architectural design.
(http://en.wikipedia.org/wiki/Light_tube)

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