What UGR is and why it decides your project

UGR stands for *Unified Glare Rating*. It is a discomfort scale: 10 is imperceptible, 19 acceptable in an office, 22 acceptable in retail and 28 is already uncomfortable. Lower is better. EN 12464-1 sets the limit for each type of space, and that figure is mandatory, not a recommendation.

The most widespread confusion: UGR is not a property of the product, even though catalogues list it as "UGR <19". The real value depends on the room: its dimensions, ceiling, wall and floor reflectances, mounting height and above all the observer’s position. The catalogue figure is calculated in a reference room (typically 4H/8H with 70/50/20 reflectances) and serves to compare products, not to justify a project.

Physically, UGR depends on the luminance of the source as seen by the eye. That is why a 5,000 lm luminaire with a deep darklight optic can have a better UGR than a 3,000 lm one with an exposed LED: what bothers you is not the lumens, it is the brightness of the surface you see.

Lowering UGR is achieved through shielding (recessing the LED, darklight reflector, greater cut-off angle) or by spreading the flux over a larger area. That is why low-glare luminaires are deeper: that depth is precisely what you are paying for.