LIGHT OUTPUT / POWER / EFFICACY
Lumens to Watts Calculator
Pick the value you need to solve for, enter the other two numbers, and get the result.
Electrical power
800 lm ÷ 100 lm/W = 8 W
Example inputs · 800 lm at 100 lm/W
THE RELATIONSHIP
The Formula
- W = lm ÷ (lm/W)
- Watts measure the electrical power the lamp uses.
- lm = W × (lm/W)
- Lumens measure the total visible light the lamp produces.
- lm/W = lm ÷ W
- Luminous efficacy measures how much light comes from each input watt. The unit is lumens per watt (lm/W).
Where to Find Your Numbers
Use total light output and total power for the same lamp or fitting. Data sheets usually list both. A bare light panel might skip driver power, which means the electronics that run it. Use your lamp's numbers, not a generic multiplier. Do not mix part and complete unit data.
DOE: luminous efficacy and input power ↗TRY PUBLISHED DATA
Measured Examples
These 2015 OLED lamp tests come from independent DOE/PNNL CALiPER lab reports.
| Test sample | Test date | Output | Input | Try values |
|---|---|---|---|---|
| 15-13 Aerelight | 3 Dec 2015 | 270 lm | 9.6 W | |
| 15-14 Ceiling Acuity Brands Lighting | 2 Dec 2015 | 332 lm | 7.4 W |
The results use published rounded inputs. Extra decimal places do not increase measurement precision.
The report lists rounded efficacy as 28 and 45 lm/W; the calculator divides the published output by input power.
HOW THE RESULT IS MADE
Method
Results show up to three decimals. Any positive number under 0.001 shows as <0.001, while zero shows as 0. Remember, total light output alone cannot predict how much light actually reaches your desk.
Source notes
- U.S. Department of EnergyLuminous efficacy definition and formula.
- DOE / PNNL CALiPER Report 24 (PDF)September 2016, supplemented August 2017. Tables 1–2 on PDF page 9, printed page 6: test dates and measured values.