Module about Basics of illumination engineering.pdf

EE3044D
Electrical System Design for Buildings
Module 2
Illumination Engineering

Illumination schemes – types of light sources and
lighting arrangements – energy efficiency in lamps
and illumination – design of lighting for various
purposes.

Physical Processes Employed in Artificial Sources
1. Incandescence
• Thermoluminescence is by definition radiation at high temperature (hot body
radiation)
• The sources employing this process are Incandescent lamp, Gas lamp
• They lead to a continuous spectrum of radiation.
2. Luminescence
• Luminescence is emission of light that does not produce heat (cold body
radiation)
• It can be caused by chemical reactions, electrical energy or subatomic motions.
• Chemiluminescence, Bioluminescence, Electroluminescence are different
types of Luminescence.
• Here color of radiation depends on the material employed.
• Usually this process leads to line or band spectrum.

3. Fluorescence
• Fluorescence is a process in which radiation is absorbed at one wavelength
and radiated at another wavelength.
• In most cases, the emitted light has a longer wavelength than the absorbed
radiation.
• Fluorescent lamp
4. Phosphorescence
• Phosphorescence is defined as emission of light from a substance exposed to
radiation and persisting as an afterglow after the exciting radiation has been
removed.
• Examples of this process are Luminous paints that contain calcium sulfide that
lead to Phosphorescence.
• They produce light radiation after exposure to light.

• Good efficient lighting is obtained by combining Luminescence and
Fluorescence.
• Intensity depends on gas or vapor involvedand phosphor material.
• The temperature of the material also play a role in radiation.

Terms used in Illumination
1. Light
2. Luminous flux
3. Lumen
4. Plane angle
5. Solid angle
6. Steradian
7. Candle power
8. Luminous intensity reduction factor
9. Glare
10. Lamp efficiency

Light
• That part of radiant energy from a hot/cold body which produces visual sensation
on human eye is called light.
Luminous Flux
• The total quantity of radiant energy per second responsible for visual sensation
from a luminous body is called Luminous Flux.
• It is represented as F or Φ
• Measured in lumens.

Lumen
• One lumen is defined as the luminous flux emitted per unit solid angle from a
point source of one candle power.
Solid Angle
• The angle subtended by the partial surface area of a sphere at its centre is
called as solid angle.
• It is measured in steradians
• It is equal to the ratio of area of the surface to the square of radius of sphere
• ω = area of surface/square of radius
=A/r2 steradians

Steradian
• The unit of solid angle.
• One steradian is defined as the solid angle that is subtended at the centre
of a sphere by its surface having area equal to radius square.

Candle Power
• The light radiating capacity of a source is called its candle power
• The number of lumens given out by a source per unit solid angle in a given
direction is called its candle power.
• It is denoted by C.P
• Total flux emitted = C.P * solid angle

Luminous Intensity
• Luminous intensity in any particular direction is the luminous flux emitted by
the source per unit solid angle in that direction.
• It is denoted by I
• Its unit is candela
• Luminous intensity of source in a particular direction, I = φ / ω

Reduction Factor
• Reduction factor of a source of light is the ratio of its mean spherical candle
power to its mean horizontal candle power.
• Reduction factor = MSCP/ MHCP
MEAN SPHERICAL CANDLE-POWER
• A unit of measure that represents the average output of a light source measured
in all directions (360°)
• MSCP= F/4π
MEAN HORIZONTAL CANDLE-POWER
• The average value of the candle-power of a light source in all directions in a
horizontal plane through the source

Illumination (Illuminance)
• When light falls on a surface, it becomes visible, the phenomenon is called as
illumination.
• It is defined as luminous flux falling on a surface per unit area.
• It is denoted by E
• Measured in lux (lumen per square meter)
• E = Ф /A

Lux
• One meter candle or lux is defined as the illumination produced by a uniform
source of one CP on the inner surface of a sphere of radius one meter.

Luminance
• It is a parameter related to the source.
• It is the intensity of light emitted from a surface per unit area in a given
direction
• Measured in cd/m2
• It can be interpreted as analogous to Brightness (B).
• L = I / A

Glare
• In the human eye, the opening of pupil is controlled by the intensity of light
received by the eye.
• If the eye is exposed to a very bright source of light, the pupil of the eye
contracts automatically in order to reduce the amount of light admitted and
prevent damage to the retina. This effect is called glare.
• Glare is defined as the brightness within the field of vision so as to cause
discomfort and interference in vision.

Lamp Efficiency
• It is defined as the visible radiations emitted by it in lumens per watt.
Depreciation factor
• Defined as the ratio of illumination when everything is clean to illumination
under normal working conditions.
• Due to accumulation of dust on lamp they emit less light
• Depreciation factor should always be greater than 1.
Utilization factor or coefficient of utilization
• Defined as the ratio of total lumens reaching the working plane to total lumens
given out by the lamp.

Law of Illumination
• The illumination on a surface depends upon
• Luminous intensity
• Distance between the source and surface
• Direction of rays of light
• It is governed by following laws :
1. Inverse square law
2. Lambert’s cosine law

Inverse Square Law
• It states that the illumination of a surface is inversely proportional to the square of
the distance of the surface from the source.
• E 
𝟏
𝐝𝟐
• E =
𝐈
𝐝𝟐
Where
I - Luminous intensity of source
d – distance of point from the source

Lambert’s cosine Law
• This law states that the illumination on any surface is proportional to the cosine of
angle between the direction of the incident flux and perpendicular to the area.
• E  cosθ
• E =
𝐈
𝐝𝟐 cosθ
Where,
I - Luminous intensity of source
d – distance of point from the source

Illumination at point ‘P’ is given by
Substituting for r,
Now we get
Where, I/h2 is the illumination at any point located directly below the source of light.

Design consideration of a good lighting scheme
• The required illumination level
• Selection of required lamp and fitting
• The size of the room
• The condition under which the illumination is used

Lighting Design
• Short hand method
• Long hand method
• Simplified method

Short hand method
• It is assumed that average maintained quantity of lumens arriving on the work
plane is the half the quantity of new lamp lumens.
• This method assumes normal sized rooms.
• Normal sized room is the one in which mounting height is less than half the
smallest room dimension.
• It is also assumed that conventional room fixtures are used.
• Spacing should not be more than mounting height for high bay fixtures and 1.5
times the mounting height for low bay fixtures.

Short hand method
Total number of fixtures (luminaries) to be used is then calculated as:

Long hand method
• More accurate and effective method of estimating the number of light
fixtures and their spacing
• The core idea of this method is the determination of coefficient of
utilization on the concept that the area to be lighted has three cavities
or spaces that have effective reflectance with respect to each other and
work plane.

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