ILLUMINATION
The act of illuminating, or supplying with light.
Terms and definitions
Luminous Intensity (I):- luminous intensity in any given direction is the luminous flux
emitted by the source per unit solid angle. Unit- candela
Luminous Flux (F):- Total quantity of light energy emitted per second form a luminous body.
Unit- lumen
Illuminance (E):- The amount of light falling on a surface. Unit-lux (lumen/m²).
Candle Power (C.P):- It is the light radiating capacity of a source in a given direction and is
defined as the number of lumens given out by the source in a unit solid angle in a given
direction. CP-lumes/watt
Laws of Illumination
The Inverse Square Law:-
The Illuminance (E) at any point on a plane perpendicular to the line joining the point and
source is inversely proportional to the square of the distance between the source and plane.
E = l/d2
Cosine Law (Lambert's Cosine Law)
Illuminance at a point on a plane is proportional to the cosine of the angle of light incident
(the angle between the direction of the incident light and the normal to the plane).
E = Iø /d2
Cosine Law: E ø = E* cos(ø)
, Lighting schemes
1. Direct Lighting
2. Semi-Direct Lighting
3. Semi-Indirect Lighting
4. Indirect Lighting
5. General Lighting
1. Direct Lighting
Most commonly used type of lighting scheme
In this sceme more than 90 percent of total light flux is made to fall directly on the working
plane with the help of deep reflectors.
Though it is most efficient but causes hard shadows and glare.
Mainly used for industrial and general out-door lighting.
2. Semi-Direct Lighting
60 to 90 percent of the total light flux is made to fall downwards directly with the help of
semi- direct reflectors, remaining light is used to illuminate the ceiling and walls.
Best suited to rooms with high ceilings where a high level of uniformly distributed
illumination is desirable.
3. Semi-Indirect Lighting
60 to 90 percent of total light flux is thrown upwards to the ceiling for diffuse reflection and
the rest reaches the working plane.
This lighting scheme is with soft shadows and glare free.
Mainly used for indoor light decoration purposes.
4. Indirect Lighting
More than 90 percent of total light flux is thrown upwards to the ceiling for diffuse reflection
by using inverted or bowl reflectors.
The ceiling acts as the light source, and the glare is reduced to minimum.
The resulting illumination is softer and more diffused, the shadows are less prominent and
the appearance of the room is much improved over that which results from direct lighting.
The act of illuminating, or supplying with light.
Terms and definitions
Luminous Intensity (I):- luminous intensity in any given direction is the luminous flux
emitted by the source per unit solid angle. Unit- candela
Luminous Flux (F):- Total quantity of light energy emitted per second form a luminous body.
Unit- lumen
Illuminance (E):- The amount of light falling on a surface. Unit-lux (lumen/m²).
Candle Power (C.P):- It is the light radiating capacity of a source in a given direction and is
defined as the number of lumens given out by the source in a unit solid angle in a given
direction. CP-lumes/watt
Laws of Illumination
The Inverse Square Law:-
The Illuminance (E) at any point on a plane perpendicular to the line joining the point and
source is inversely proportional to the square of the distance between the source and plane.
E = l/d2
Cosine Law (Lambert's Cosine Law)
Illuminance at a point on a plane is proportional to the cosine of the angle of light incident
(the angle between the direction of the incident light and the normal to the plane).
E = Iø /d2
Cosine Law: E ø = E* cos(ø)
, Lighting schemes
1. Direct Lighting
2. Semi-Direct Lighting
3. Semi-Indirect Lighting
4. Indirect Lighting
5. General Lighting
1. Direct Lighting
Most commonly used type of lighting scheme
In this sceme more than 90 percent of total light flux is made to fall directly on the working
plane with the help of deep reflectors.
Though it is most efficient but causes hard shadows and glare.
Mainly used for industrial and general out-door lighting.
2. Semi-Direct Lighting
60 to 90 percent of the total light flux is made to fall downwards directly with the help of
semi- direct reflectors, remaining light is used to illuminate the ceiling and walls.
Best suited to rooms with high ceilings where a high level of uniformly distributed
illumination is desirable.
3. Semi-Indirect Lighting
60 to 90 percent of total light flux is thrown upwards to the ceiling for diffuse reflection and
the rest reaches the working plane.
This lighting scheme is with soft shadows and glare free.
Mainly used for indoor light decoration purposes.
4. Indirect Lighting
More than 90 percent of total light flux is thrown upwards to the ceiling for diffuse reflection
by using inverted or bowl reflectors.
The ceiling acts as the light source, and the glare is reduced to minimum.
The resulting illumination is softer and more diffused, the shadows are less prominent and
the appearance of the room is much improved over that which results from direct lighting.
