Point-source intensity for a target illuminance calculator

Required normal-direction luminous intensity is calculated as E × d². Use the stated system boundary and matching input units.

Units

I = E \times d^{2}

Calculator

Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.

Given

I = 100 \times {50}^{2} = 250{,}000

Symbol	Meaning	Unit
$I$	required normal-direction luminous intensity	cd
$E$	target normal illuminance	fc
$d$	source-to-task distance	ft

Results are estimates for study and screening. Check the inputs, units and assumptions before you use them for design, billing or contract decisions.