Illumination

A lamp produces an illumination of 10 lux at a point 10 m directly below it. What is its luminous intensity?

A standard candle emits a total luminous flux of _ lumens.

An unshaded lamp is placed at a distance \(r_1\) above the ground and produces an illumination \(E_1\) at a point on the ground directly below the lamp. At what angle must the lamp be aimed on the ground to produce an illumination one-half of \(E_1\)?

Four lamps are suspended 6 m above the ground at the corners of a lawn 4 m on each side. If each lamp emits 250 cd, calculate the illumination at the center of the lawn.

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

Calculate the distance from a normally placed screen a 30 candela lamp be placed in order that the illumination be 5 lux.

An office 17m by 8m wide, is lighted by 8 lamps has a luminous intensity of 200 Cd. Allowing an absorption loss of 4,000 lm for the reflectors, walls and ceiling, Calculate the average illuminations on the working plane.

A medium unshaded lamp hangs 8 m directly above the table. To what distance should it be lowered to increase the illumination to 2 times its former value?

Calculate the mean spherical candle power of a lamp emitting a flux of 1,500 lumens.

A lamp produces an initial illumination of 800 lux over a normally placed screen. If the distance of the lamp from the screen is doubled, what is the new illumination on the screen?

An office 15 m by 8 m is lighted by 8 lamps, each with a luminous intensity of 200 cd. Allowing an absorption loss of 4,000 lm for the reflectors, walls and ceiling, calculate the average illumination on the working plane.

A lamp produces an illumination of 10 lux at point 10 m directly below it. What is luminous intensity of the lamp?

A room 8 m × 12 m is lighted by 15 lamps to a fairly uniform illumination of 100 lumens per square meter. What is the coefficient of utilization if the output of each lamp is 1,600 lumens?

A lamp has a luminous efficiency of 11 lm/watt and gives out a luminous flux of 275 lm. What is the wattage of the lamp?

A uniform source of light gives 1,884 lumens and is suspended 4 m above the center of a floor 3 m square. Find the illumination in lm/m² at the floor level directly below the lamp.

Two lamps having luminous intensities of 250 and 300 candelas respectively are placed 100 m apart. Lamp A is 10 m above the ground while lamp B is 20 m above the same level. What is the illumination at ground level midway between the lamp posts?

A road is illuminated by two 500 candela lamps placed 6.1 m above the center line of the road and 18.3 m apart. Find the illumination produced on the surface of the road at a point on the center line midway between the lamps.

A 100 watt, 230 volt gas filled lamp has a mean spherical candlepower of 92. Find its efficiency in lumens per watt.

An office, 17m by 8m, is lighted by 10 lamps and each lamp has a luminous intensity of 200 cd. Allowing an absorption loss of 5,000 lm for the reflectors, walls, and ceilings, calculate the average illumination on the working plane.

A colliery workshop 20 m x 10 m requires an average illumination of 135 lm/m² on the working plane. Calculate the electrical power and current required for the purpose. Allow a coefficient of utilization of 0.45 and a depreciation factor of 1.4. The supply is 230-V at 50 Hz and the efficiency of each of the lamps is 12 lm/W.