Calculates illuminance from a point source using the inverse square law: E = I cos θ / d², where I is luminous intensity in candelas. At 1 m from a 100 cd point source perpendicular to the surface: E = 100 lux — the inverse square law means doubling the distance reduces illuminance to 25%.
Inputs
I Cd
Reference formula or conversion factor shown for context.
D M
Separation between two points or total path length. Check that units are consistent throughout the calculation.
Theta Deg
Reference formula or conversion factor shown for context.
Refl Pct
Reference formula or conversion factor shown for context.
Results
horizontal illuminance E_h (lux)
Sample size or count used in the calculation.
horizontal illuminance (foot-candles)
Sample size or count used in the calculation.
vertical illuminance E_v (lux)
Sample size or count used in the calculation.
luminance of surface L (cd/m²)
Sample size or count used in the calculation.
E_h = I/d² · cos(θ)
Reference formula or conversion factor shown for context.
typical targets
Reference formula or conversion factor shown for context.