Lumens to Watts Calculator
Estimate electrical power using luminous flux and your lamp’s efficacy.
Formula
watts = lumens / efficacy (lm/W)
Luminous flux (lm): 800 lm · Electrical power (W) ≈ (800 lm)÷(100)
How to use
- Enter the luminous flux in lumens.
- Enter the specified efficacy in lm/W.
- Read estimated electrical watts.
Examples
- 800 lm at 100 lm/W requires 8 W.
Frequently asked questions
Is there one conversion factor?
No. Efficacy depends on the lamp and driver.
Which efficacy should I enter?
Use lumens divided by input watts for the complete lamp or fixture.
Does this measure brightness on a surface?
No. Illuminance also depends on distance and light distribution.
Sources
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