About the Luminous Efficacy Calculator
Lumens per watt of a lamp, with how it compares to other lighting technologies.
Also known as: lumens per watt, lamp efficiency calculator, lighting efficacy, bulb efficiency.
How to use this calculator
- Enter light output, power consumption.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
efficacy = lumens ÷ watts
Worked example
Using the values pre-filled in the calculator above:
- Light output = 800 lm
- Power consumption = 9 W
the calculator returns:
- Luminous efficacy: 88.89 lm/W
- Technology match: Standard LED
- Energy rating band: F
- Watts for 1000 lumens: 11.25