UGR Glare Rating Explained: Why It Matters for Office and Commercial Lighting

Unified Glare Rating (UGR) is one of the most overlooked specifications in commercial lighting design. It measures the discomfort glare experienced by occupants in a space. Get it wrong and your tenants complain about headaches, screen reflections, and eye strain. Get it right and the lighting disappears into the background, doing its job without anyone noticing.

What Is UGR?

UGR is a standardised metric defined by CIE (Commission Internationale de l'Eclairage). It quantifies the likelihood of glare from luminaires in a given room geometry. The scale runs from roughly 10 (imperceptible glare) to 30+ (intolerable glare). Lower numbers mean less glare.

UGR is not a property of the luminaire alone. It depends on the room dimensions, surface reflectances, luminaire position, and viewing direction. A fitting that scores UGR<19 in one room layout might score UGR 22 in another. That said, luminaire manufacturers test against a standardised reference room (CIE 117:1995) so you have a consistent baseline for comparison.

UGR Limits by Application

BS EN 12464-1 sets maximum UGR values for different tasks and spaces:

For open-plan offices, UGR<19 is the standard you need to hit. Most modern LED panels and recessed downlights from quality manufacturers achieve this. Budget fittings often do not.

How UGR Is Calculated

The formula considers the luminance of each luminaire in the field of view, the background luminance from walls and ceiling, the solid angle of each source, and the observer's position. In practice, you do not calculate UGR by hand. Lighting design software (DIALux, Relux) computes it automatically from the luminaire's photometric data (IES or LDT files) and your room model.

This is why accurate photometric data matters. If your LDT file does not reflect the real luminance distribution, your UGR calculation will be wrong. EMPRICS provides verified LDT files for every product family, downloadable from each product page and our Technical Resources hub.

Reducing UGR in Practice

Several design strategies lower UGR in a space:

Use low-glare optics. Luminaires with recessed light sources, micro-prismatic diffusers, or dark-light reflectors push the luminance below the critical angle. Look for fittings specifically rated UGR<19.

Increase ceiling reflectance. A white ceiling (reflectance 0.7+) raises background luminance, which reduces the contrast ratio between luminaire and surroundings. Dark ceilings make any fitting look more glaring.

Avoid direct line of sight. Position luminaires so occupants are not looking directly at the bright face. In open-plan offices, orient linear luminaires parallel to the window wall and perpendicular to the main viewing direction.

Use indirect or direct/indirect distribution. Luminaires that throw light upward onto the ceiling create a large, low-luminance source instead of a small, bright one. Direct/indirect pendants are excellent for achieving UGR<16 in demanding applications.

UGR vs Other Glare Metrics

You might encounter other glare measurements. Visual Comfort Probability (VCP) is the North American equivalent but uses a different scale. GR (Glare Rating) applies to outdoor and sports lighting. For UK and European commercial interiors, UGR is the standard referenced in building regulations and BREEAM assessments.

Specifying UGR for Your Project

When writing a lighting specification, state the maximum UGR for each zone. Include it alongside your lux level, CRI, and colour temperature requirements. Your lighting designer will use this as a constraint when selecting fittings and running calculations.

EMPRICS product pages display UGR ratings where available. Filter by UGR on our collection pages to find fittings that meet your project requirements. Every product includes downloadable LDT files for accurate DIALux calculations.

Browse our full range or request a specification quote for your project.