Discussion
The luminous efficacy of an electric light bulb is measured in which one of the following units?
Answer: A
Luminous efficacy is measured in lumen W-1.
Luminous efficacy is the luminous flux emitted (lumens) per watt of electrical power drawn. A filament lamp gives about 15 lm/W and an LED lamp well over 100 lm/W.
Lumen per square metre is lux, the unit of illuminance; lumen W-1 h-1 mixes in time, which efficacy does not involve; and the candela measures luminous intensity in a given direction, not total flux.
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