MCQs on Illumination


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01․ The range of visual spectrum is
300nm - 1000nm.
480nm - 1000nm.
480nm - 760nm.
300nm - 760nm.

The visual spectrum lies in between the UV spectrum on its left to Infra-red spectrum to its right. Its range is 380nm -760nm.

02․ Which lamp has a negative Colour Rendering Index (CRI)?
LED
Fluorescent
High pressure sodium vapour
Low pressure sodium vapour

Low pressure sodium vapour lamp has a monochromatic spectrum and therefore has a negative CRI.

03․ A 1000 W bulb fitted with a reflector illuminates an area of 3 m x 3 m with an average illumination of 450 lux. If the bulb has and efficiency of 9 lumens / watt the efficiency of the reflector is
70 %.
30 %.
20 %.
45 %.

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04․ What will be the total flux emitted by a source of 60 candle power?
754.2 lumens.
0.001326 lumens.
60 lumens.
None of these.

Total flux = (4 X 3.14 X 60) lumens = 754.2 lumens.

05․ From a uniform light source having luminous intensity of 300 candelas, there exists a plane surface 15 m below. The value of illuminance at a point on the plane surface where the luminous flux rays are inclined at an angle of 30 to the surface is
1.53 lux.
1.15 lux.
58.45 Kilolux.
17.32 lux.

From the laws of illumination, Illuminance = Intensity × cosine of the angle of inclination of light rays/ Distance2 E = I Cosθ/d2 = 300 × cos 30/225 = 1.15 lux

06․ The solid angle subtended by an area of 2400 cm2 on the surface of a sphere of diameter 1.2 m is
3 / 2.
1 / 3.
2 / 3.
2 / 5.

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07․ In illumination technology total lumens emitted by source / total lumens available after waste of light is equal to
waste light factor.
utilization factor.
beam factor.
absorption factor.

Total lumens emitted by source / total lumens available after waste of light is equal to waste light factor. It is about 1.2 for rectangular area, 1.5 for irregular objects - statues, monuments etc.

08․ The illumination at a point 5 meters below a lamp in 6 lux. The candle power of the lamp is
30
140.
150.
200.

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09․ Which among the following lamps has the maximum burning hours?
LED.
Incandescent.
Metal halide.
Compact Fluorescent.

LEDs have very high burning hours of about 500000 hours.

10․ A 200 candle power lamp is hung 4 m above the centre of circular area of 5 m diameter. The illumination at centre of the area is
13.5 lux.
12.5 lux.
17.5 lux.
18.5 lux.

According to law of inverse square the illumination can be given as,
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