1. ILLUMINATION

2. Principles of good lighting
Aims of good lighting is
To promote work and other activities carried on with in the building.
To promote the safety of people using the building
To create a pleasing environment in conjunction with the structure and decoration.

3. Realisation of the aims
By careful planning of the brightness and colour pattern, attention can be naturally drawn to important areas.
By controlling direct and indirect glare from light sources to eliminate visual discomfort.
By minimising flicker from discharge lamps
Correlating the light throughout the building to prevent excessive differences between adjacent areas and to avoid accidents.
By installing emergency light systems where ever necessary.

4. Types of lighting schemes
1.Direct lighting
More than 90% of light in a room is made to fall on the working plane with the help of deep reflectors.
2. Semi-Direct lighting
Most of the light produced by the fittings is directed downwards and a certain amount of light is directed upwards.
3. Semi-Indirect lighting
% of total light flux is thrown upwards to the ceiling for diffuse reflection and the rest reaches the working space directly. This lighting scheme is glare free.

5. Contd… Indirect Lighting
In this more than 90% of total light flux is thrown upwards to the ceiling for diffuse reflection by using inverted or bowl reflectors.
ceiling acts as a light source, and the glare is reduced to minimum.
Illumination is more diffused, shadows are less prominent and appearance of the room is much improved.
Used for decoration purposes in cinemas, theatres ,hotels and in workshops where large machines and other obstructions would cause troublesome shadows if direct lighting is employed.

6. Classification of Lamps
1.Incandescent Lamps
2. Discharge Lamps
A) Fluorescent lamps
B) Sodium Lamp
C) High Pressure Mercury vapour lamp

7. Comparison between Tungsten filament lamps & Fluorescent lamps
Voltage fluctuation has more effect on light output.
Luminous efficiency increases with increase in wattage of the lamp.
Due to high working temperature heat radiations are present.
It has less effect since the variations in voltage are absorbed in the choke.
Luminous efficiency increases with increase in wattage and increase in the length of the tube.
Low working temp and hence heat radiation is low.

8. Contd… Normal life is 7,500 working hours.
Initial cost per lamp is high.
For the same lumens output lesser number of tubes is required,the wiring cost is low,.
Normal life is working hours
Initial cost per lamp is low.
For the same lumens output more number of lamps are required,the wiring cost is high.

9. Terminology in illumination
The power or strength of the source of light is known as Luminous Intensity (I) and is measured in candela.
From light source energy is radiated in the form of light waves.
The flow of light from the source is known as Luminous Flux (F) and its unit is lumen.
Lumen is the luminous flux emitted in a solid angle by a source of one candle power.
Lumens = Candle power x solid angle

10. Contd….
When the light emitted by a source falls on a surface, it is illuminated. Illuminance (E) or illumination is the light falling on a surface is measured in lux.
Illumination = = = where ω =

11. Laws of illumination
Consider a source placed at a distance 1m away from the surface to be illuminated,
The amount of light falling on the surface area is proportional
(i) directly to the power of the source.
ie., when the power (Luminous Intensity, I)of the source is increased,
illumination of the surface is also increased
(ii) Inversely to the square of the distance between the source and the surface to be illuminated(inverse square law)
ie., Illumination (E) = I/r2
If the plane to be illuminated is not normal to the direction of luminous flux, and is inclined at an angle θ then,
illumination (E) = I cosθ/r2 (cosine law)
This is called cosine law which states that the illumination on a surface is proportional to the cosine of the angle between the normal to the surface and the line of flux.

12. Design considerations of a Good Lighting Scheme.
1.Intensity of illumination
The intensity of illumination required for different types of work differ.ISI had recommended various illumination levels for various parts of building and various occupancies.
2. Selection of luminaires
A luminaire is the apparatus which distributes, filters or transforms the light given by a lamp.
In small premises tubular fluorescent lamps or tungsten filament lamps can be used. In large premises high intensity sources such as mercury vapour lamp or sodium discharge lamps.
Depending on the type of illumination required (direct, indirect, diffusing etc.)

13. Contd…
3. Size of the room
Lumen output of the sources is not fully utilized at the work place. Part of it is lost in the fittings. This is taken into account by a factor known as the co-efficient of utilisation.
Coefficient of utilization depends on the lumen output of the fitting , size and shape of the room, reflection factors of walls and ceiling, height of the ceiling, arrangement of the fittings etc.
4. Mounting Height & spacing of Luminaries
The mounting height will be largely be governed by the type of building and type of lighting scheme employed.
Spacing of luminaries is important to provide uniform illumination over the whole area.

14. Contd…. 5. Conditions of use
Dust and dirt of the surroundings may get deposited on the light fittings and hence lamp efficiency is deteriorate.
Depreciation Factor =

15. Calculation of illumination
The number of lamps to be installed to obtain the desired level of illumination can be calculated by the following methods.
1.Watts per square metre method
It is an approximate method of calculating the watts per square metre of area to be illuminated on the basis of illumination level desired at the place
2. Lumen or light flux method
This is applicable to sources of light which produce an approximately uniform illumination over the workplane
Total lumens received on the work plane = no: of lamps x wattage of each lamp x efficiency of each lamp in lumens /watt x coefficient of utilisation x maintenance factor

16. Calculation of illumination
Point to point or inverse square law method
Where N is the number of fittings needed
E –required illumination in lux
A= working area
O= luminous flux produced per lamp (lumens)
CU= coefficient of utilization
MF= Maintenance factor