Knowledge ·
UGR and glare control in interiors
What the Unified Glare Rating measures, why it belongs to a room rather than a luminaire, and the optical features that bring it down.
Glare is the most common complaint about interior lighting, and the least visible on a plan.
What UGR is
The Unified Glare Rating (CIE 117) estimates discomfort glare for an observer in a given position. It depends on the luminance of the luminaires seen, their size and position in the field of view, and the background luminance of the room. Typical limits in EN 12464-1:
- UGR ≤ 19 — offices, reading, screen work
- UGR ≤ 22 — retail sales areas, reception
- UGR ≤ 25 — circulation, storage
Because UGR depends on the room, a catalogue "UGR < 19" usually refers to a standard reference room. Always calculate it for the real layout.
How optics reduce glare
- Deep-set sources: the LED sits further back in the housing, raising the cut-off angle.
- Black or dark-finished baffles and reflectors: reduce visible brightness at the aperture.
- Honeycomb louvres: block light at oblique viewing angles for accent spotlights.
- Diffusers with microprismatic structure: spread luminance over a larger area.
Beyond the luminaire
Lighter walls and ceilings raise background luminance and lower UGR. Lighting vertical surfaces is often the cheapest glare control there is.