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.

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)}

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)}