Photometrics Calculator
Free photometric calculator for average illuminance from lumens, room area, and light loss. A design check, not a full lighting layout. No signup.
About this calculator
How to estimate average illuminance
A photometric calculator turns lamp lumens into an average light level on the work plane. This one uses the zonal-cavity form of the lumen method:
lux = (number of luminaires × lumens each × CU × LLF) ÷ area in square metersCU is the coefficient of utilization from the luminaire report for your room cavity. LLF is the light-loss factor (lamp lumen depreciation, dirt, and similar). The result is a room average, not the light level at a desk in the corner.
Worked example
Ten luminaires, 4,000 lumens each, CU 0.60, LLF 0.80, room 50 square meters:
10 × 4,000 × 0.60 × 0.80 = 19,200 lumens on the plane
19,200 ÷ 50 = 384 luxCommon questions
What is a photometric calculator?
It estimates average illuminance from luminaire lumens, how much of that light the room actually uses, and the floor area. It does not replace a point-by-point photometric study or the manufacturer's IES file.
Is the photometric calculator free?
Yes. It runs in the browser with no signup. The phone lux meter elsewhere in the toolbox is a camera estimate, not this calculation.
For design, installation, or safety decisions, verify assumptions against the applicable code edition, equipment documentation, and site requirements.
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