How to convert electric power in watts (W) to luminous flux in lumens (lm).
You can calculate lumens from watts and luminous efficacy.
Watt and lumen units represent different quantities, so you can't convert watts to lumens.
The luminous flux ΦV in lumens (lm) is equal to the power P in watts (W), times the luminous efficacy η in lumens per watt (lm/W):
ΦV(lm) = P(W) × η(lm/W)
So
lumens = watts × (lumens per watt)
or
lm = W × (lm/W)
What is the luminous flux of a lamp that has power consumption of 60 watts and luminous efficacy of 15 lumens per watt?
ΦV = 60 W × 15 lm/W = 900 lm
| Light type | Typical luminous efficacy (lumens/watt) |
|---|---|
| Tungsten incandescent light bulb | 12.5-17.5 lm/W |
| Halogen lamp | 16-24 lm/W |
| Fluorescent lamp | 45-75 lm/W |
| LED lamp | 80-100 lm/W |
| Metal halide lamp | 75-100 lm/W |
| High pressure sodium vapor lamp | 85-150 lm/W |
| Low pressure sodium vapor lamp | 100-200 lm/W |
| Mercury vapor lamp | 35-65 lm/W |
Energy saving lamps have high luminous efficacy (more lumens per watt).