Define UGR — What Is UGR?

统一眩光值UGR是什么

Ask an office worker why a lighting installation "feels harsh," and they will rarely point to lux levels. They will describe bright ceiling fixtures stabbing into their peripheral vision, or reflections washing out their monitor. That sensation — discomfort glare — is exactly what UGR was created to measure. When you define UGR limits correctly in a specification, you are engineering visual comfort, not just brightness.

How Does UGR Work? The Formula Behind the Rating

To define UGR mathematically, CIE 117-1995 gives the following formula:

Three practical consequences follow directly from this formula, and they matter more than the equation itself when you define UGR requirements for a real project:

1. Luminance beats lumens. Because L is squared, a small, intensely bright aperture (a bare-chip LED downlight) can produce far worse glare than a large, low-luminance panel emitting the same total flux. This is why "glare control" is fundamentally about spreading emission over area or shielding it from view.
2. UGR is observer-dependent. The same room scores differently for an observer looking lengthwise versus crosswise, seated versus standing. CIE and EN 12464-1 evaluate seated observers (eye height 1.2 m) at the walls looking across the room, in both the transverse and axial directions, and report the worst case.
3. A dark room makes glare worse. Lowering L_b — dark ceilings, dark walls, no indirect component — raises UGR even if the fixtures are unchanged. Adding an uplight component or lightening surface reflectances is often the cheapest way to bring a failing installation into compliance.

The Tabular Method: How Manufacturers Publish UGR

Because the full formula requires a room model, CIE 117-1995 also defines a simplified tabular method. The manufacturer's photometric lab computes UGR for a matrix of standard room sizes (expressed as X·H and Y·H multiples of mounting height above eye level), fixed reflectances (typically ceiling 0.7, walls 0.5, floor 0.2), and a standard luminaire spacing-to-height ratio of 0.25. The result is the UGR table you see in photometric datasheets.

When a datasheet says "UGR < 19," it means the tabular value for a reference room (commonly 4H/8H) is below 19 — not that the fixture guarantees UGR ≤ 19 in your room. To define UGR compliance for a specific project, a designer must run the calculation in software such as DIALux or Relux using the actual room geometry, reflectances, and layout. This distinction is the single most common source of disputes between specifiers and suppliers.

📊 Key Data: UGR Scale and Application Limits

Practical Applications by Industry

Office & Commercial Workspaces

This is where UGR bites hardest. EN 12464-1 requires UGR ≤ 19 for screen-based office work, and workstation ergonomics standard ISO 9241-307 adds limits on luminaire luminance reflected in displays. In practice, compliant open-plan offices use 600×600 mm or linear LED panels with micro-prismatic (MPO) diffusers or low-luminance louvres, keeping luminance below roughly 3,000 cd/m² at angles above 65° from vertical. Opal-diffuser panels that look "soft" to the eye frequently fail UGR 19 in large rooms because their total luminance is high in every direction. When you define UGR targets for offices, always require project-specific DIALux/Relux calculations for the worst-case observer, not just a "UGR<19" datasheet badge.

Education & Healthcare

Classrooms require UGR ≤ 19 with 300–500 lx; the challenge is that both children and teachers change viewing directions constantly, so worst-case orientation matters. In healthcare, examination areas typically demand UGR ≤ 19 while patient rooms need special care: a patient lying supine looks directly at the ceiling, a geometry the standard UGR method does not model well. EN 12464-1 addresses this with luminance limits for luminaires in the patient's field of view (e.g., shielded or indirect fixtures above beds) rather than relying on the seated-observer UGR calculation alone.

Industrial & Logistics

High-bay installations at 8–14 m mounting height benefit from the position index: fixtures far above the line of sight glare less, so UGR ≤ 22 to ≤ 25 is achievable even with high-output fixtures. The risk zone is low-bay areas (4–6 m) with narrow-beam, high-luminance LED fixtures aimed near-horizontal viewing lines — forklift operators looking upward along racking aisles routinely experience the glare that the seated-observer method underestimates. Specify diffuse or prismatic optics for aisle lighting and define UGR ≤ 22 for sustained-work zones such as picking and packing stations.

Sports, Retail & Hospitality

Indoor sports halls follow EN 12193, which uses glare rating limits adapted to upward viewing angles (players tracking a ball look directly toward the ceiling). Retail accepts higher UGR (≤ 22) in sales areas because sparkle and contrast are part of merchandising — but checkout and back-office areas revert to office-grade UGR ≤ 19. Hospitality generally designs well below the limits, using indirect and low-luminance sources, because perceived comfort is the product being sold.

How to Reduce UGR: 6 Mitigation Strategies

1. Lower the luminaire luminance. Choose micro-prismatic diffusers, parabolic louvres, or "dark-light" reflector optics that cut luminance above 65° elevation. This attacks the squared L term directly — the highest-leverage intervention available.
2. Add an indirect component. Direct/indirect pendants (e.g., 70/30 split) raise background luminance L_b and reduce contrast between fixture and ceiling, often dropping UGR by 2–4 units.
3. Raise mounting height. Greater height increases the position index p and shrinks the solid angle ω, both of which reduce UGR.
4. Lighten room surfaces. Moving ceiling reflectance from 0.5 to 0.8 and walls from 0.3 to 0.5 raises adaptation luminance and can rescue a marginal design without changing a single fixture.
5. Orient and zone luminaires. Linear fixtures viewed end-on present less luminous area than viewed broadside; align them with the dominant viewing direction and keep fixtures out of the 0–53° glare-critical zone ahead of fixed workstations.
6. Use more, smaller, dimmer sources. Distributing flux across more low-output fixtures reduces per-fixture luminance, typically at modest cost premium.

Limitations: What UGR Does Not Measure

To define UGR honestly, you must also state its boundaries. UGR quantifies discomfort glare, not disability glare (the veiling luminance that physically reduces task visibility, treated separately by CIE via threshold increment TI in road lighting). It applies to interior installations with luminaires larger than 0.005 m² and smaller than about 1.5 m² of luminous area — very small sources (bare LED points) and very large sources (luminous ceilings) fall outside the validated range, and CIE 147 / CIE 232:2019 discuss corrections for small and non-uniform sources. UGR also ignores daylight glare (use DGP — Daylight Glare Probability — instead) and reflected glare on glossy tasks or screens, which EN 12464-1 handles through separate luminance limits.

Key Standards

• CIE 117-1995 — Discomfort Glare in Interior Lighting. The founding document that defines UGR, its formula, the position index, and the tabular method. Every UGR table in every photometric file traces back to this publication.
• EN 12464-1:2021 — Light and lighting — Lighting of work places — Part 1: Indoor. Sets the binding UGR limit (R_UGL) for each task and activity type in Europe: ≤ 16, ≤ 19, ≤ 22, ≤ 25 depending on visual demand.
• CIE S 017:2020 — International Lighting Vocabulary (ILV). Provides the normative definitions of glare, discomfort glare, and unified glare rating used in contracts and specifications.
• CIE 190:2010 and CIE 232:2019. Calculation and application guidance for UGR, including corrections for non-uniform LED luminaires whose bright chips dominate perceived glare despite low average luminance.
• ISO 8995-1 / CIE S 008. The joint ISO/CIE workplace lighting standard applying UGR limits internationally, mirroring EN 12464-1 values.
• IES LM-63 / EULUMDAT. Photometric file formats from which UGR tables are computed; verify data comes from IES LM-79-19 goniophotometer measurement, not simulation.

Key Takeaways