## How to convert lux to watts

How to convert illuminance in lux (lx) to electric power in watts (W).

You can calculate watts from lux, luminous efficacy and surface area.

Lux and watt units represent different quantities, so you can't convert lux to watts.

- Lux to watts calculation with area in square feet
- Lux to watts calculation with area in square meters
## 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 illuminanceE_{v}in lux (lx) times the surface areaAin 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 efficacyηin 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 areaAin square feet (ft^{2}), divided by the luminous efficacyηin 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= 0.09290304×50lx× 200ft^{2}/ 15lm/W = 61.94W## Lux to watts calculation with area in square meters

The luminous flux

Φ_{V}in lumens (lm) is equal to the illuminanceE_{v}in lux (lx) times the surface areaAin 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 efficacyηin 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 areaAin square meters (m^{2}), divided by the luminous efficacyηin 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= 50lx× 18m^{2}/ 15lm/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 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

## See also