Light output divided by electrical input power. Incandescent lamps managed about 15 lm/W and fluorescent systems 60 to 100; LED luminaires commonly reach 100 to 150 lm/W or more. Source efficacy and luminaire efficacy differ, because optics, housings and drivers lose light and power, and energy codes and utility rebates are written against luminaire efficacy measured by LM-79.
Efficacy on the new troffer is 138 lm/W, so we can drop the connected load by a third and still hit 400 lux.
Efficacy has units, lumens per watt; efficiency is a dimensionless ratio. Using efficiency for lm/W marks a speaker as an outsider.
Also heard as
- efficacy
- lm/W
- lumens per watt
- LPW
Related terms
Luminous flux
The total amount of visible light a source emits in all directions, weighted for the eye's sensitivity and measured in lumens.
LM-79
The standard method for measuring a complete LED luminaire's light output, power, efficacy, color and distribution.
LED
Light-Emitting Diode: a semiconductor light source, made white for lighting by coating a blue chip with phosphor.
Driver
The electronic power supply that converts line voltage into the regulated current or voltage an LED needs.
Droop
The fall in an LED's efficiency as drive current or temperature rises, so extra power yields proportionally less light.