# 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 1

What is the luminous flux of a lamp that has power consumption of 30 watts and luminous efficacy of 15 lumens per watt?

ΦV = 30 W × 15 lm/W = 450 lm

#### Example 2

What is the luminous flux of a lamp that has power consumption of 50 watts and luminous efficacy of 15 lumens per watt?

ΦV = 50 W × 15 lm/W = 750 lm

#### Example 3

What is the luminous flux of a lamp that has power consumption of 70 watts and luminous efficacy of 15 lumens per watt?

ΦV = 70 W × 15 lm/W = 1050 lm

#### Example 4

What is the luminous flux of a lamp that has power consumption of 100 watts and luminous efficacy of 15 lumens per watt?

ΦV = 100 W × 15 lm/W = 1500 lm

#### Example 5

What is the luminous flux of a lamp that has power consumption of 200 watts and luminous efficacy of 15 lumens per watt?

ΦV = 200 W × 15 lm/W = 3000 lm

## Luminous efficacy table

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).

Lumens to watts calculation ►