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Which of the following statements are correct about the maintenance factor? I) It is the ratio of illumination under normal working condition to the total lumen given out by the lamp. II) It is the ratio of illumination under normal working condition to the illumination when the things are perfectly clean. III) The accumulation of dust, dirt and smoke on the lamp decreases the maintenance factor. IV) It is the ratio of illumination when the things are perfectly clean to the illumination under normal working condition.
Statements III and IV
Statements I and III
Only Statement II
Statements II and III
Statements II and III
The maintenance factor is defined as the ratio of illumination on a working plane under actual (normal) conditions to the illumination when the luminaire is perfectly clean. It accounts for the gradual reduction in light output due to the accumulation of dust, dirt, and depreciation of the lamp and luminaire surfaces over time.
IS 1944:1970 (Code of Practice for Lighting of Public Thoroughfares)
The maintenance factor is defined as the ratio of illumination on a working plane under actual (normal) conditions to the illumination when the luminaire is perfectly clean. It accounts for the gradual reduction in light output due to the accumulation of dust, dirt, and depreciation of the lamp and luminaire surfaces over time.
Maintenance┬аFactor=Illumination┬аwhen┬аperfectly┬аcleanIllumination┬аunder┬аnormal┬аconditionsтАЛ
Depreciation┬аFactor=Maintenance┬аFactor1тАЛ
As luminaires operate, environmental contaminants like dust and smoke accumulate on reflectors and lamp surfaces, increasing absorption and reducing reflection efficiency. Since the maintenance factor is less than unity (typically between 0.6 and 0.8), illumination engineers use it to over-design the initial lighting system to ensure that the average illumination remains above the required level throughout the maintenance cycle.
The maintenance factor is always less than 1.
Higher maintenance factor values indicate a cleaner environment or more frequent cleaning intervals.
Accumulation of dust and dirt inversely affects the luminous output efficiency.
Maintenance factor is distinct from the utilization factor, which relates to the geometry of the room and luminaire efficiency.
Prevents under-lighting over the service life of the system.
Helps in scheduling cost-effective maintenance and cleaning intervals.
Requires initial over-design of the lighting system which can increase capital expenditure.
Hard to estimate precisely as it depends on environmental variables.
Design of indoor lighting installations.
Street lighting calculations.
Industrial plant illumination planning.
Option I is incorrect as it refers to lamp output rather than illumination on the working plane.
Option IV is the reciprocal of the maintenance factor, which represents the depreciation factor.
D is correct тАФ Statements II and III correctly define the maintenance factor and its relationship with environmental depreciation.
Always remember: Maintenance factor is the ratio of actual to clean conditions, whereas depreciation factor is the ratio of clean to actual conditions (the reciprocal).
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