what is Illuminance E ?

The unit of measurement is the lux [lx]: E = F / A F = luminous flux in lumenensA = area illuminated in m2 Illuminance E is the ratio between the luminous flux and the area to be illuminated. An illuminance of 1 lx occurs when a luminous flux of 1 lm falls evenly on an area of 1 m². Based on the definitions for illuminance luminous intensity and solid angle W = A/r2, we obtain the following formula for illuminance: E = I / r2Photometric inverse square law r = distance of the light source to the object in mA = area illuminated in m2I = luminous intensity in Candela It is assumed that the light falls perpendicular to the surface it illuminates. If the surface is at an angle a then E = I/r2 must be multiplied by cos a.