Illuminance from a Point Source

Calculate illuminance in lux and foot-candles at a distance from a lamp using the inverse square law, free online.

Luminous intensity (candela)

Distance (m)

Surface tilt from facing the lamp (°)

About this calculator

For a point source of luminous intensity I (candela) the illuminance on a surface facing it at distance d is E = I ÷ d² lux. If the surface is tilted by angle θ the value is multiplied by cos θ. 1 foot-candle = 10.764 lux.