# 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 *Φ*_{V} in lumens (lm) is equal to the power P in watts (W), times the luminous
efficacy * η* in lumens per watt (lm/W):

*Φ*_{V(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?

*Φ*_{V} = 60W × 15lm/W = 900lm

## 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 | 30-90 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).