Calculate Unified Glare Rating (UGR) for any room and luminaire combination. Check compliance against EN 12464-1 limits for offices, classrooms, healthcare, and industrial spaces — with anti-glare measure recommendations to bring UGR within spec.
Please enter room dimensions, luminaire luminance, and illuminance.
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How to read a UGR number
UGR runs roughly from 10 to 30+. Lower is calmer; higher means the fixtures increasingly pull your eye and cause discomfort. Your result above is plotted on this same scale.
| UGR | Perceived glare | Typical verdict |
|---|---|---|
| Under 10 | Imperceptible | Glare not noticed at all |
| 10–16 | Comfortable | Good for sensitive visual tasks |
| 16–19 | Acceptable | The office / classroom target |
| 19–22 | Noticeable | Starts to feel glary over time |
| 22 and up | Uncomfortable | “Why does this room interrogate me?” |
Recommended UGR by space (EN 12464-1)
| Space | Aim for |
|---|---|
| Office / workstation | UGR ≤ 19 |
| Classroom / education | UGR ≤ 19 |
| Healthcare — exam & precision | UGR ≤ 16 |
| Technical drawing / labs | UGR ≤ 16 |
| Reception / general interior | UGR ≤ 22 |
| Industrial / warehouse | UGR ≤ 25 |
| Retail | Variable — control display & spill glare directly |
Why LED fixtures often feel harsher
A fixture can be perfectly compliant on lumens yet still feel painful, because glare is about luminance (brightness per unit area), not total light. LEDs concentrate output into tiny, intense surfaces:
Tiny emitting surface
The same lumens leave a far smaller area than an old fluorescent tube — so luminance (cd/m²) skyrockets.
Very high peak luminance
A bare diode can exceed 1,000,000 cd/m² — orders of magnitude past what feels comfortable.
Exposed diodes
Without a diffuser you look straight at point sources, each a sharp hotspot.
Weak optics
Cheap fixtures skip shielding or prismatic control, leaving the source visible at glare angles.
Same lumens, very different comfort
How the source is shielded and spread matters more than its wattage. Left to right, roughly worst to best for direct glare:
The UGR formula, in plain terms
It looks fierce, but it only says four things matter:
| Term | What it means |
|---|---|
| L (luminance) | Source brightness — squared, so it dominates. Lower-luminance fixtures help the most. |
| ω (solid angle) | Apparent size. A diffuser trades a bigger area for much lower L — a net win. |
| p (position index) | How close the source is to your line of sight. Sources overhead and to the side glare less. |
| Lb (background) | Brighter surroundings shrink the contrast. Light walls and ceilings genuinely reduce glare. |
Simplified estimate for guidance — a full UGR uses the manufacturer’s luminance data per viewing angle. Use a fixture’s UGR table for specification.