Unified Glare Rating (UGR) is the CIE standard metric for assessing discomfort glare caused by luminaires in indoor environments. Scale: 10 (imperceptible) to 30 (unbearable). Office standard: UGR<19 (EN 12464-1). For VDT (screen-based) workspaces: UGR<16 recommended. UGR depends on luminaire luminance, background luminance, observer position, and room dimensions. Mitigation: use micro-prismatic diffusers, indirect lighting, or increase mounting height. UGR values are typically provided in luminaire photometric data (IES/LDT files).