Which of the following is defined as the ratio of the total number of lumens reaching the working plane to the total number of lumens emitting from the source?

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  1. Coefficient of utilisation or utilisation factor
  2. Depreciation factor
  3. Space to height ratio
  4. Maintenance factor

Answer (Detailed Solution Below)

Option 1 : Coefficient of utilisation or utilisation factor
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Concept:

Luminous efficiency: It is also known as radiant efficiency. It is defined as the ratio of energy radiated in the form of light, which produces the sensation of vision to the total energy radiated out by the luminous body.

Radiant efficiency = energy radiated in the form of light / total energy radiated by the body

Maintenance factor: It is defined as the ratio of illumination under normal working conditions to the illumination when everything is clean.

Its value is always less than 1, and it will be around 0.8. This is due to the accumulation of dust, dirt, and smoke on the lamps due to which they emit less light than that they emit when they are clean. Frequent cleaning of lamps will improve the maintenance factor.

Depreciation factor: It is defined as the ratio of initial illumination to the ultimate maintained illumination on the working plane.

Depreciation factor = 1 / maintenance factor

Its value is always more than 1.

Coefficient of utilization or utilization factor: It is defined as the ratio of the total number of lumens reaching the working plane to the total number of lumens emitting from the source.

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