Photometric & Optics
Illuminance Uniformity Calculator
Analyze how evenly light is distributed across a surface. Click any cell to edit its lux value, or paste a CSV/tab-delimited grid. The heatmap and uniformity ratios update instantly.
Grid Settings
Columns 4
Rows 4
Presets
š” Click any cell to edit its lux value directly.
ā
Uā Ratio
Min / Average
ā
Uā Ratio
Min / Max
ā
lux
Average
ā
lux
Min ā Max
Why the average lux hides the truth
Two rooms can report the same 500 lux average and feel completely different. The average says nothing about distribution — uniformity does. Both grids below average 500 lux:
Smooth — comfortable
510
490
505
495
500
500
505
490
505
Average 500 lux · Uo 0.98 — excellent
Patchy — hotspots & shadows
900
150
900
150
500
150
900
150
700
Average 500 lux · Uo 0.30 — poor
Same average, wildly different experience: the patchy room has glaring bright spots and dim corners that cause eye fatigue and uneven visibility. That gap is exactly what the ratios above measure.
The uniformity ratios
| Ratio | What it tells you |
|---|---|
| Min / Avg (Uo) | Overall uniformity — the EN 12464-1 metric. Worst point against the average. |
| Min / Max (Ud) | Diversity — how severe the darkest-to-brightest contrast is. |
| Avg / Max | How close the average sits to the brightest point — overall balance. |
Reading the Uo ratio
| Uo | Quality |
|---|---|
| 0.8 and up | Excellent |
| 0.6 – 0.8 | Good |
| 0.4 – 0.6 | Fair |
| Under 0.4 | Poor |
The formula
Uo = EminEavg
The worst-lit point divided by the average. Closer to 1.0 means flatter, more even light.
Recommended uniformity by space
| Space | Aim for (Uo) |
|---|---|
| Classroom / education | 0.7+ |
| Office / workstation | 0.6+ |
| Healthcare / precision | 0.7+ |
| Warehouse / industrial | 0.5+ |
| Roadway (carriageway) | 0.4+ |
| Parking lot | 0.25 – 0.4 |
| Sports field | Very high (0.5 – 0.8 by play level) |
The misconception worth unlearning
Better uniformity isn't "brighter"
Uniformity is about consistency — comfort, visibility and reduced fatigue — not maximum lux. You can raise the average and still fail uniformity if you just add brighter hotspots. Spacing, beam spread and mounting height fix evenness; more wattage does not.