Correct Answer - Option 1 : Maintenance factor
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 lamp 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 total number of lumens reaching the working plane to the total number of lumens emitting from source.
Space to height ratio in illumination is defined as the ratio of the distance between adjacent luminaires (centre to centre), to their height above the working plane. It should be around 1.2.
