Illumination

An unshaded lamp is 6 m above a table. It is lowered down by 2 m. By how much is the illumination on the table increased?

A medium unshaded lamp hangs 8 m directly above the table. To what distance should it be lowered to increase the illumination to 4.45 times its former value?

A floodlight emitting 25,000 candelas in the center of its beam is aimed at 60° to a point on the ground 20 meters away. The illumination of the point in lux is

An unknown lamp placed 6 m from a photometer screen provides the same illumination as a 90-cd lamp placed 4 m from the screen. What is the candlepower of the unknown lamp?

Luminaires of 2000 lumens output will be installed in a room. The desired illumination is 200 foot-candle. The coefficient of utilization is 0.45 and maintenance factor is 90%. Determine the number of luminaires needed if the size of the room is 120 m².

A hall 30 m long and 12 m wide is to be illuminated and the illumination required is 50 meter-candles. Calculate the number of lamps required taking a depreciation factor of 1.3 and utilization coefficient of 0.5 given that the output of the lamp to be used is rated 100 W, 1615 lumens.

The floor area of a room is 10 meters by 10 meters. The desired illumination level is 150 lux. Assume the coefficient of utilization is 0.51, the maintenance factor is 0.95 and in the market a fluorescent luminaire provide 1200 lumens output of light. Determine the number of luminaires needed for the room.

The study of illumination involves

The luminous flux emitted in unit solid angle by a uniform point source having a luminous intensity of 1 candela is called

The luminous intensity is defined as

The luminous intensity of a lamp is expressed in

The illumination at a point a surface is the luminous flux per unit area of the surface and its unit is

Low pressure in a fluorescent tube is obtain by

The illumination of a surface is

The first object of a lighting system is to provide adequate illumination on the working space. For proper design, the effects of the surroundings must be taken into account and the factors are

To use lumen method of design, you must first find

Maintenance factor or depreciation factor takes account of

Another requirement of good lighting scheme is that it makes the principal object the brightest thing in the field of vision. An illumination ratio of 10 : 3 :1 has been suggested as the best for

The principle of working of a high pressure mercury vapour lamp is that

Although the average efficiency of a 400W high pressure mercury vapour lamp is high but its main disadvantages are