What Is UGR? Unified Glare Rating for Office and School Lighting

What UGR measures — and predicts

UGR — unified glare rating, defined in CIE 117 — is a number that predicts the discomfort glare a person will experience from the luminaires in a room: the squint-and-shift feeling of a ceiling full of bright fittings above a screen. The calculation weighs the luminance of each luminaire in the viewer's field of vision, its apparent size and position relative to the line of sight, and the room's background brightness. The resulting scale runs roughly from 5 to 30, and lower is better: UGR 22 feels acceptable in a warehouse, UGR 19 is the classic office requirement, UGR 16 approaches gallery restraint.

The subtlety that catches buyers: UGR is a property of a room, not of a luminaire. The same fixture can meet UGR 19 in one geometry and miss it in another, because ceiling height, room size, spacing, surface reflectances and viewing direction all enter the formula. What manufacturers legitimately publish is a UGR table — the computed UGR for a set of standard rooms (defined dimensions, 70/50/20 percent ceiling-wall-floor reflectances, standard arrangement) with that luminaire. Reading "UGR<19" on a datasheet without asking for the table is accepting a claim without its evidence.

The limits that govern offices and schools

EN 12464-1, the European workplace lighting standard, attaches UGR limits to visual tasks, and those limits flow directly into tender documents worldwide. The commonly quoted targets:

Values are illustrative of EN 12464-1 practice; confirm against the current edition of the standard and any national annexes for the project's market.

Two clarifications prevent tender-stage confusion. First, UGR addresses discomfort from luminaires seen directly; it does not score reflected glare — the screen reflections that plague glossy monitors — which is handled by luminaire luminance limits (the "luminaire at 65°-75°" requirements in EN 12464-1 practice) and by layout. Second, UGR is not the road-lighting glare measure: streets use TI (threshold increment) under EN 13201, a different formula for disability glare. The office-side design workflow around these limits is walked through in our EN 12464-1 office guide and the classroom application in the classroom guide.

How luminaires actually reach UGR 19

Glare control is optical engineering plus discipline. The levers manufacturers pull: deep recessing, so the source sits above the ceiling plane and the ceiling itself shields steep viewing angles; louvers and micro-prismatic diffusers on panels, which shear luminance in the critical 45-85° zone where screens catch fittings; low-luminance linear optics, engineered to fall below roughly 3,000 cd/m² at the angles screens see — the usual definition of a "screen-optimized" or UGR19-class linear; and snooted or baffled downlights that black out the visible source. Alongside optics, layout matters: tighter spacing at lower output usually beats sparse fittings at high output, because glare grows with per-fixture luminance faster than comfort grows with evenness.

The cost side is worth naming: glare control costs efficacy and money. A louvered UGR19 panel delivers fewer lumens per watt than a bare-diffuser panel, and a deep-recess downlight costs more than a surface disc. Specifying UGR 19 everywhere — including corridors and stores where 22 or 25 is appropriate — is a quiet budget leak.

Reading a UGR table without squinting

A typical table crosses room shapes with mounting height: columns for room proportions (say 2H, 4H and 8H room widths), rows for heights, each cell the computed UGR for a standard array. Two habits make the table usable. First, read the cells nearest your real room, not the best cell on the page — catalogs quote the most favorable corner, and a fixture showing UGR 19 in one cell may show 21 in another. Second, treat the table as a screening tool: it assumes 70/50/20 reflectances and a regular layout, which real rooms rarely honor. The decisive document remains the layout calculation run in your geometry — the table earns the fixture onto the shortlist, the DIALux run earns it into the tender.

Screens deserve their own conversation

Modern office glare control adds a luminaire-level criterion that UGR tables do not capture: the luminance the fixture presents to screens at steep angles, where monitors catch ceiling fittings in reflection. Current practice classifies linears and panels by their luminance at 65° and 75° against thresholds — the <3,000 cd/m² class being the common "screen-optimized" mark, with stricter classes for demanding control rooms and trading floors. A scheme can pass a UGR 19 calculation and still trigger complaints if steep-angle luminance is high; tenders for screen-heavy workspaces therefore increasingly specify both the UGR limit and the luminance class, and buyers should expect factories to supply luminance data on request.

What to request from a supplier

Because the number depends on the room, the deliverable that matters is documentation, not a badge. Request: the UGR table for the fixture in standard rooms, per EN 13032-style photometry; the photometric files (IES and LDT) so the project's actual geometry can be run in DIALux or Relux; for screen-heavy areas, the luminaire luminance data at the critical angles; and a layout calculation for the real room — dimensions, reflectances, furniture plan — showing achieved UGR, not a catalog room. Suppliers who produce these routinely are the ones whose "UGR<19" survives an inspection. Certification by destination (CE, UKCA, SAA, SASO) is issued via certified partner factories and verifiable by number and database link; the compliance matrix sits in our certification guide, and the fixture families that carry these optics are indexed in our office and education and commercial lighting lines.

Illustrative commercial terms: samples of 1-5 pcs ship in 7-14 days; trial orders run 100-200 pcs per SKU; bulk production 25-40 days after deposit; pricing quoted per project. Photometric files and UGR tables are supplied as standard with sample documents, before any commitment.

Education tenders show why the paperwork discipline matters. A classroom package — louvered panels or low-luminance linears at UGR 19, flicker performance on the same report, CCT and CRI fixed, controls for teaching scenes — is priced and awarded on documents, then judged by parents and teachers on comfort years later. The gap between those two moments closes only if the calculation delivered at tender matches the fixtures shipped: same optics, same diffuser, same driver. That is the practical case for named-model photometry and golden-sample inspection on every glare-critical order — the same discipline that governs bins and drivers applies to optics, because a swapped diffuser is a different luminaire as far as glare is concerned.

Common buyer mistakes

• Treating "UGR<19" as a fixture property. It is a computed room result; without the UGR table and real-room calculation, the claim is untested.
• Confusing UGR with reflected glare. Screen reflections need luminance data and layout, not just a UGR table.
• Importing road-lighting habits. TI is the street metric; UGR belongs to interiors.
• Specifying UGR 19 everywhere. Corridors, stores and industrial spaces tolerate higher values; over-specifying costs efficacy and budget.
• Assuming low UGR means dim. Glare control redistributes light; a UGR19 room can be brighter and more comfortable than an uncontrolled one at the same lux.