How to use the light bulb efficacy and energy calculator
Find how efficiently a bulb turns power into light and how much energy it uses per year. Enter light output, electrical power, hours used per year in the fields above; the luminous efficacy, energy used per year are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “bulb efficiency lumens per watt”, “LED vs incandescent”, “annual lighting energy”, “calculate light bulb efficacy and energy”, “find luminous efficacy”.
Formula
Variables
- lm — Light output (lm)
- W — Electrical power (W)
- hrs — Hours used per year (h)
Worked example
With light output = 800 lm, electrical power = 9 W, hours used per year = 1000 h, the calculator gives luminous efficacy ≈ 88.88889 lm/W; energy used per year ≈ 9 kWh.
Frequently asked questions
What is the light bulb efficacy and energy calculator used for?
Find how efficiently a bulb turns power into light and how much energy it uses per year. It helps with questions such as “bulb efficiency lumens per watt”, “LED vs incandescent”, “annual lighting energy”.
What is the formula for the light bulb efficacy and energy calculation?
Luminous efficacy (lm/W) = lm / W. Energy used per year (kWh) = W × hrs / 1000. Here lm is light output (lm), W is electrical power (W), hrs is hours used per year (h).
What inputs do I need for the light bulb efficacy and energy calculator?
You need light output in lm, electrical power in W, hours used per year in h. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the light bulb efficacy and energy calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the light bulb efficacy and energy result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.