Electrical convertions

How to convert watts to lumens

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.

Watts to lumens calculation formula

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)

Example

What is the luminous flux of a lamp that has power consumption of 60 watts and luminous efficacy of 15 lumens per watt?
ΦV = 60W × 15lm/W = 900lm

Luminous efficacy table

Light typeTypical
luminous efficacy
(lumens/watt)
Tungsten incandescent light bulb12.5-17.5 lm/W
Halogen lamp16-24 lm/W
Fluorescent lamp45-75 lm/W
LED lamp30-90 lm/W
Metal halide lamp75-100 lm/W
High pressure sodium vapor lamp85-150 lm/W
Low pressure sodium vapor lamp100-200 lm/W
Mercury vapor lamp35-65 lm/W

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