Convert lamp lumens to electrical watts from luminous efficacy.
| Watts | – |
Use this when a pack quotes lumens and you want the electrical draw. Watts = lumens ÷ (lm/W). 800 lumens at 100 lm/W is 8 W. A typical LED is 80–120 lm/W; an old incandescent is nearer 12–15 lm/W. Watts are heat and the bill; lumens are the light you see.
Lumens: Light output of the lamp.
lm/W: Luminous efficacy, lumens per watt. Must be greater than zero.
Watts: Electrical power the lamp draws at that efficacy.
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