Definition
Glare in lighting is the sensation produced by luminance (brightness) within the visual field that is sufficiently greater than the luminance to which the eyes are adapted, causing discomfort, annoyance, or reduced visual performance. Two distinct types exist: (1) Discomfort glare — the 'this light is annoying' sensation that doesn't necessarily impair vision. Measured by UGR (Unified Glare Rating, CIE 117) for indoor spaces and GR (Glare Rating, CIE 112) for outdoor/sports. (2) Disability glare — veiling reflections that reduce contrast and visibility, particularly problematic for computer screens (reflections of bright luminaires washing out the display) and driving (oncoming headlights at night). Glare is the #1 complaint in office lighting — even when illuminance levels are correct, excessive luminaire luminance above 65° from vertical creates unacceptable glare for seated occupants.
Key Data
| Parameter | Value / Explanation |
|---|---|
| Discomfort glare (UGR) | Rate 5-40. UGR ≤19 for offices, ≤16 for CAD/design, ≤22 for industrial. EN 12464-1 standard. |
| Disability glare (veiling) | Luminance at angles >65° from vertical should be <1,000 cd/m² for screen-based offices. |
| Causes | Excessive luminaire luminance, poor shielding, incorrect mounting height, high contrast ratios |
| Mitigation strategies | Micro-prismatic optics, indirect/direct distribution, deeper recessing, baffles, lower lumen packages |
| Outdoor glare (GR) | GR ≤50 for sports, ≤45 for roadway. CIE 112 standard. Different metric than UGR. |
Application Guide
Open-plan office
UGR ≤19, luminaire luminance <1,000 cd/m² at >65°, indirect/direct mix
Screen-based workers spend 6-8h/day under these lights; glare causes headaches and reduced productivity
Sports stadium (broadcast)
GR ≤50, precise aiming with spill control, flicker-free for slow-motion cameras
Glare impairs player performance and broadcast quality; flicker causes banding in super-slow-motion replay
Roadway / street lighting
TI (Threshold Increment) ≤15%, G-class per CIE 115, full-cutoff optics
Disability glare from streetlights directly impacts driver safety at night
Conclusion & Procurement Recommendation
For B2B procurement: glare control is a luminaire design issue, not a room design issue — you can't fix a high-glare luminaire by mounting it differently. Key specifications: (1) Request the luminaire's UGR table (not just 'UGR <19') showing values at standard room sizes and reflectances, (2) For offices: specify luminance limits at ≥65° from vertical (the 'uncomfortable zone' for seated occupants), (3) Request photometric diagrams showing the luminance distribution (cd/m² per viewing angle), not just the intensity distribution (candela), (4) For screen-based offices: specify 'low-luminance' or 'dark-light' optics — these use precise prismatic structures to redirect light below 65° while appearing dark at higher angles.