MCQs on Illumination

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01․ Illumination can be expressed in

Light is the cause and illumination is the effect of light on which it falls i.e., when light falls upon the surface, this process is called illumination. It is given as no. of lumen falling on a surface per unit area. It is expressed in lux or meter candle.

02․ Luminous efficacy of a typical HPSV lamp is in between
40 - 70 lm/watt.
70 - 120 lm/watt.
120 - 200 lm/watt.
10 - 40 lm/watt

The typical lumen package of a HPSV lamp is 8000 lumens and its power rating is 70-150W.

03․ Total flux or lumens required in any lighting scheme depends inversely on
utilization factor.
reduction factor.
reflection factor.
none of the above.

All the light emitted by the source does not reach the surface to be illuminated. Some of light directly falls on the surface some of the light reaches the surface and some of light never reaches the surface to be illuminated as it is getting absorbed. \

04․ Wave length for red colour is around
400 nm.
500 nm.
600 nm.
700 nm.

Red colour lies at the extreme right hand side end of the visual spectrum. So its wavelength is highest than any other colour.

05․ Unit of luminous flux is

Luminous flux is defined as the total quantity of the light energy radiated or emitted per second from a hot body in the form of light waves. It is measured in lumens.

06․ Which of the following statement is correct?
Light consists of electromagnetic waves.
Light consists of ultraviolet waves.
Light consists of infrared waves.
Light consists of gamma rays.

Light is nothing but a electromagnetic radiation which causes visual radiation to the eye.

07․ Luminous efficiency of a fluorescence lamp is
70 lumens / watt.
60 lumens / watt.
40 lumens / watt.
30 lumens / watt.

Luminous efficiency is defined as the ouput in lumens per watt of the power consumed by the source of the light. For fluorescence lamp luminous efficiency is 40 lumens / watt.

08․ The illumination of the surface varies directly with cosine of the angle between normal to surface and direction of the inclined light is given by
law of square inverse.
Lambert’s cosine law.
both A and B.
none of the above.

According to Lambars cosine law the illumination of the surface varies directly with cosine of the angle between normal to surface and direction of the inclined light.

09․ ___________________________ factor is defined as the ratio of the illumination when everything is clean to illumination under normal working conditions.
Absorption factor.

Due to the accumulation of the dirt, dust and smoke on the lamps they emits less light as compared to when they are new. Similarly walls and ceiling they reflect less light when are cover with dust. Hence to design a source of light we need to consider the depreciation factor. It is usually greater than 1.

10․ The work of ballast in a fluorescent tube is to
limit the flow of current.
provide a kick start when voltage is induced.
both ‘a’ and ‘b’.
None of these.

Ballasts are basically inductors which protect the lamp from excessive current and also gives the bulb a kickstart when voltage is induced in the coil.