Natural light and illumination This document discusses natural lighting and illumination in buildings. It explains that lighting serves three main purposes: to allow safe movement, task performance, and a pleasant interior. Buildings can be lit naturally through daylight or artificially through electric lamps. Daylight comes from sunlight or skylight. Various methods can control daylight penetration including external screens, glazing types, and interior blinds. The document also discusses illumination levels, daylight factor measurements, glare reduction, innovative daylighting technologies, and the advantages of natural lighting.

1. Natural light and illumination
SUBMITTED BY:-
DEEPTI CHAUHAN
PRN NO.-UV2200041

2. Objectives
Be aware of the energy implications of lighting.
Understand why buildings require lighting.
Understand what is meant by the term ‘daylight factor’.
Be able to identify a number of innovative daylighting technologies.
Be able to identify the advantages of daylighting.
Understand what is meant by the terms general lighting, localised lighting
and local lighting.

3. Lighting
Lighting within the indoor environment can be considered to have three basic
purposes:
To enable the occupants to work and move about in safety.
To enable tasks to be performed.
To make the interior look pleasant.
There are two principle ways in which a building can be lit. These are:
Naturally - by daylight received from the sky.
Artificially - by electric lamps or other artificial light sources.
Daylight as two distinct sources of light:
Sunlight – That part of solar radiation that reaches the earth’s surface as
parallel rays after selective attenuation by the atmosphere.
Skylight – That part of solar radiation that reaches the earth’s surface as a
result of scattering in the atmosphere.
Sunlight and skylight may therefore be considered as the direct and diffuse
components of daylight.

4. Daylighting
Daylight (both sunlight and skylight) is usually admitted into a building by the
means of windows and skylights.
The quantity of daylight obtained within a room will be dependent upon:
The orientation, geometry and space planning of the spaces to be lit.
The dimensions and orientation of the openings through which daylight will
pass.
The location and surface properties of any internal partitions which may
reflect and distribute the daylight.
The location, form and dimensions of any shading devices which will provide
protection from too much light and glare.
The light and thermal characteristics of the glazing materials used.
Atrium Rooflight
Clerestorey
Borrowed light
Window

5. Controlling daylight
A range of methods are available to control the amount of daylight that penetrates
into the building.
Fixed external – Permanently obstructs skylight and is maintenance free, but is
architecturally dominating.
Variable external – Allows the maximisation of skylight but can suffer from
maintenance problems.
Variable internal – Absorbs solar radiation and acts as a secondary heat source
within the building. Effective for visual comfort.
Various methods of controlling daylight
In addition, further control can be provided by the choice of glazing type.

6. Daylight factor
Interior daylight is measured using a parameter known as the Daylight Factor (DF).
The daylight factor is defined as:
Interior illuminance
Daylight factor (%) = ×100
Simultaneous horizontal unobstructed exterior illuminance
The Daylight Factor is a combination of 3 separate
components:
The sky component (SC) – the light received directly
from the sky.
The externally reflected component (ERC) - the light
received directly by reflection from buildings and
obstructions outside the room.
The internally reflected component (IRC) - the light
received from surfaces inside the room. DF = SC + ERC + IRC

7. Glare from daylight
Glare from daylight can be reduced by:
Using solar control devices - such as external screens and louvres, glass of low
transmittance, or internal blinds and curtains
Other methods of decreasing the contrast between the interior and the view of the
sky - such as ensuring that the window wall is light coloured.
Designed to eliminate the use of artificial light on normal days.
Average daylight factor of 2% over 80% of the office space.
Atrium has rooflights which allow natural light to enter the building.
PV façade designed to produce 25-33% of the offices electricity needs.
Designed to achieve a minimum 2% daylight factor over the office area.
Solar shading provided on South façade via motorised external translucent glass louvres.

8. Innovative daylighting technologies
A number of innovative daylighting technologies are available which are
capable of redirecting the incoming sunlight or skylight to the areas where it is
required.
Mirror system
The technologies available include:
Sunlight tracking systems - have mirrors and/or lenses
that follow the sun and redirect its light to a required
location.
− heliostat and light pipe systems.
− mirror systems.
Daylighting systems - redirect diffuse skylight and
usually sunlight as well. They generally modify or
supplement an existing window or rooflight.
− light shelves.

9. Innovative daylighting technologies
Light shelves
These can be used to redirect sunlight and skylight deep into
a space. Both interior and exterior light shelves are available.
Exterior shelves can also function as a shading device.
The performance of light shelves depends upon the proportion
of the shelf which is situated inside or outside the space.
They can also be used to control sunlight and reduce glare.
External light shelf Without light shelf
No light shelf With light shelf
Internal light shelf

10. Energy implications of daylighting
To achieve good daylighting, the glazing must be designed so that there is a correct
balance between the heat gains and losses resulting from the transmission of
thermal radiation in and out of the building and the light entering the building.
Daylight – Reduces artificial lighting load
Solar gain – Reduces winter heating load
Solar gain – Increase summer cooling load
Conduction
Convection
Radiation
Air leakage
The energy implications of daylighting
Correct daylighting design will not only reduce energy costs related to artificial
lighting, but also reduce the possibility of having to cool rooms overheated by low
efficiency lighting appliances.
However, although large glazed areas may provide sufficient daylighting at some
distance into the building, they can also cause glare, overheating and high
heating and cooling energy costs.

11. Advantages of daylighting
The utilisation of daylight in buildings has a number of advantages, namely:
It can make a significant contribution to energy efficiency.
It has a variability and subtlety which is more pleasing than the relatively
monotonous environment produced by artificial lighting.
It helps to create optimum working conditions by bringing out the natural
contrast and colour of objects.
Windows and skylights give occupants contact with the outside world.
The presence of natural light can bring a sense of well-being and
awareness of the wider environment.
It is also claimed that exposure to natural light can have a beneficial effect
on human health.
However, due to its uncertainty and variability, daylighting cannot provide
adequate illumination of the internal environment all of the time. Therefore, artificial
lighting systems must always be incorporated into buildings in order to
supplement daylighting when this is required.

12. ILLUMINATION

13. Illumination
• Tasks to be performed in the space
• Desired light levels based on the tasks performed in the space
• Room size and dimensions
• Structural obstructions such as beams
• Layout of furniture and obstructions such as partitions
• Room and object surface colors and reflectances
• Special concerns such as safety and security
• Hours of operation
• Assessment of normal operating conditions
• Possibility or known existence of abnormal operating conditions
• Cleanliness of the area during operation
• Maintenance schedule
• Availability of daylight

14. Illumination Levels

15. Illumination Levels

16. Methods of Illumination
Inverse Square Law
It states that illumination at any given surface due to a given light source is inversely proportional to
square of distance between them.
where
• E – Illuminance (Lux)
• I - Luminous Intensity (Lumens/m2 )
• r - distance of surface from light source (m)

17. Cosine Law
• E= I cos θ
d²
where
• E – Illuminance (Lux)
• I - Luminous Intensity (Lumens/m2 )
• r - distance of surface from light source (m)
• θ - angle of incidence
Coefficient of Utilization Method
F= E X A______
CU X LLD X LDD
Where
F= Lumens generated by light (lm)
E= Illumination level (Lux)
A= Area of work plane (m2)
CU= Coefficient of Utilisation (%)
LLD= Lamp lumen Depreciation (%)
LDD= Lamp Dirt Depreciation (%)