The number of square feet per light bulb increases as you go from dark walls,
ceiling and dirty lamps to white walls, ceiling and clean lamps. The number of
square feet also increases as the illuminance (in lux) increases. The number of
square feet per 60 watt 120 volt incandescent light bulb is always more at a specific
illuminance (in lux) than the number of square feet per 60 watt 130 volt incandescent
light bulb at the same specific illuminance (in lux).
Approximate number of square feet per 60 watt incandescent light bulb is based
on:
- lamps mounted 8' to 10' above floor
- power supply is 118 Vac to 122 Vac
- ambient temperature is 55 °F to 90 °F
Note:
1 footcandle = 10.76 lux
20 lux = approximately 2 footcandles
Light output depends on:
- amount of dirt on bulb surface
- reflection from ceiling, walls, floor and birds
- age of lamp relative to average rated life
- applied voltage
- frequency of lamp maintenance
- ambient room temperature
- room surface dirt build-up
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