Work out glare index instantly with clear inputs, formula shown and shareable results.
The unified glare rating formula, 8 log10(0.25/Lb x sum of L² omega / p²), weights each glare source by the square of its luminance and its solid angle, divided by the square of a position index that discounts sources away from the line of sight. Office standards typically require UGR of 19 or below.
Unified glare rating
UGR = 8 log10[(0.25 / Lb) x sum(L² omega / p²)]
Preliminary estimate only. Glare assessment for a real installation requires photometric data for the luminaires and calculation at the actual observer positions.
UGR = 8 log10[(0.25 / Lb) x sum(L² omega / p²)]. The unified glare rating formula, 8 log10(0.25/Lb x sum of L² omega / p²), weights each glare source by the square of its luminance and its solid angle, divided by the square of a position index that discounts sources away from the line of sight.
Glare is a contrast phenomenon. The same lamp is far more uncomfortable against a dark ceiling than a bright one, so raising background luminance genuinely reduces discomfort.
This calculator takes 4 inputs: Luminance of the light source, Background luminance, Solid angle of the source at the eye, Guth position index. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.