# Lux to watts calculator

Illuminance in lux (lx) to electric power in watts (W) calculator and how to calculate.

Enter the illuminance in lux, luminous efficacy in lumens per watt, surface area in square feet / meters or spherical radius in feet / meters and press the Calculate button to get the power in watts:

* the predefined luminous efficacy values are typical / average values.

## Lux to watts calculation formula

### Lux to watts calculation with area in square feet

The luminous flux *Φ*_{V}
in lumens (lm) is equal to 0.09290304 times the illuminance *E*_{v} in lux (lx) times the surface area *A* in square feet (ft^{2}):

*Φ*_{V(lm)} =
0.09290304* *×*
E*_{v(lx)}* *×*
A*_{(ft}2_{)}

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

*P*_{(W)} = *Φ*_{V(lm)}* *
/* η*_{(lm/W)}

So the power P in watts (W) is equal to the 0.09290304 times the illuminance *E*_{v} in
lux (lx) times the surface area *A* in square feet (ft^{2}), divided by the luminous
efficacy * η* in lumens per watt (lm/W):

*P*_{(W)} = 0.09290304* *×*
E*_{v(lx)}* *×*
A*_{(ft}2_{)} /* η*_{(lm/W)}

So

watts = 0.09290304* *×*
*lux* *× (square feet) / (lumens per watt)

or

W = 0.09290304* *×*
*lx* *× ft^{2} / (lm/W)

#### Example

What is the power consumption with illuminance of 50 lux, luminous efficacy of 15 lumens per watt and surface area of 200 square feet?

*P* =
0.09290304* *×*
*50 lx* *× 200 ft^{2} / 15 lm/W = 61.94 W

### Lux to watts calculation with area in square meters

The luminous flux *Φ*_{V}
in lumens (lm) is equal to the illuminance *E*_{v} in lux (lx) times the surface area *A* in square meters (m^{2}):

*Φ*_{V(lm)} = *E*_{v(lx)}* *×* A*_{(m}2_{)}

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

*P*_{(W)} = *Φ*_{V(lm)} /* η*_{(lm/W)}

So the power P in watts (W) is equal to the illuminance *E*_{v} in lux (lx) times the surface area *A* in square meters (m^{2}), divided by the luminous
efficacy * η* in lumens per watt (lm/W):

*P*_{(W)} = *E*_{v(lx)}* *×* A*_{(m}2_{)} /* η*_{(lm/W)}

So

watts = lux* *× (square meters) / (lumens per watt)

or

W = lx* *× m^{2} / (lm/W)

#### Example

What is the power consumption with illuminance of 50 lux, luminous efficacy of 15 lumens per watt and surface area of 18 square meters?

*P* = 50 lx* *× 18 m^{2} / 15 lm/W = 60W

## 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 |