UGR<19 is the single most misquoted number in office lighting. A luminaire does not "have" UGR 19 — the rating is produced by a specific room, mounting height and viewing direction. This guide explains what the standard actually requires, how the number is generated, which optics reach it, and how to specify it so the installed result matches the datasheet.
What UGR actually measures
UGR (Unified Glare Rating) quantifies discomfort glare — the distraction and eye fatigue caused by bright luminaires against a darker ceiling background. It is a calculated value defined by CIE Publication 117, not a property you can measure on a single fixture in isolation.
The calculation weighs four things: the luminance of each luminaire in the field of view, the solid angle it subtends at the observer's eye, its position relative to the line of sight (the Guth position index), and the background luminance of the room. Change the room and the same fixture produces a different UGR.
What EN 12464-1 requires
EN 12464-1 (Light and lighting — Lighting of work places, Part 1: Indoor work places) sets a maximum UGR limit (UGRL) per task, alongside minimum maintained illuminance and colour rendering. For screen-based office work the limit is 19. It is a ceiling, not a target: UGR 16 is compliant, UGR 22 is not.
| Task area | Maintained illuminance Ēm | Max UGRL | Min CRI (Ra) |
|---|---|---|---|
| Office — writing, typing, data processing | 500 lx | 19 | 80 |
| Office — conference / meeting rooms | 500 lx | 19 | 80 |
| Office — filing, copying, circulation | 300 lx | 25 | 80 |
| Classrooms | 300 lx | 19 | 80 |
| Healthcare — examination rooms | 1000 lx | 19 | 90 |
| Retail — sales areas | 300 lx | 22 | 80 |
| Industrial — precision assembly | 750 lx | 19 | 80 |
| Warehouse — aisles, occupied | 150 lx | 22 | 60 |
Values are the common reference figures for these task groups. Always confirm against the current edition of the standard and any national annex for the destination market.
How optics actually reach UGR<19
Low glare comes from controlling luminance at high viewing angles — specifically between 65° and 90° from nadir, the band that lands in a seated worker's field of view. There are three mainstream approaches, and they trade efficacy for control in different ways.
Opal / diffuse film
Lowest cost- Typical UGR
- 22–25 (rarely <19)
- Efficacy penalty
- 10–20%
- Appearance
- Uniform milky panel
- Best for
- Corridors, retail, back-of-house
Micro-prismatic
Best balance- Typical UGR
- <19 in standard rooms
- Efficacy penalty
- 5–8%
- Appearance
- Sparkle-free, slightly textured
- Best for
- Offices, classrooms, healthcare
Honeycomb louver
Strictest control- Typical UGR
- <16 achievable
- Efficacy penalty
- 15–25%
- Appearance
- Dark cell, very low brightness
- Best for
- Control rooms, CAD, studios
The efficacy penalty is real and must be designed for. If a 36 W panel delivers 4,000 lm as an opal version and 3,700 lm as a micro-prismatic one, the lighting layout needs either more fixtures or a higher-output driver to hold 500 lx on the working plane. Specifying UGR<19 without re-running the calculation is how projects end up compliant on glare but short on illuminance.
How to specify it so the installed result matches
- 1
Define the task
Identify the task area and pull its Ēm, UGRL and Ra from EN 12464-1. Screen work is 500 lx / UGR 19 / Ra 80.
- 2
Request the photometric file
Ask for the IES or LDT file of the exact SKU — not a similar model. Without it, no one can verify the claim.
- 3
Model the real room
Run DIALux or Relux with your actual dimensions, ceiling height, reflectances and workstation orientation. The UGR table from a 4H/8H reference room is a starting point, not an answer.
- 4
Check both viewing directions
UGR is directional. Confirm the limit is met crosswise and endwise to the luminaire axis, in the directions people actually face.
- 5
Verify on site
After installation, confirm illuminance on the working plane and review for reflected glare on screens, which UGR does not capture.
What UGR does not tell you
UGR covers discomfort glare from luminaires viewed directly. It says nothing about reflected glare — the mirror image of a bright fixture in a monitor or a glossy desk — which is often the real complaint in an office. It also assumes an empty rectangular room with uniform reflectances, so partitions, dark carpet and glazed walls all shift the real-world result.
- Reflected glare on screens is controlled by luminaire placement and luminance, not by the UGR figure alone.
- Very low UGR with a dark ceiling can feel gloomy — some upward component (or a suspended up/down luminaire) improves perceived brightness.
- Flicker is a separate comfort issue entirely; specify driver flicker performance alongside UGR.
Frequently asked questions
The questions below cover what buyers and specifiers ask us most often about anti-glare office lighting.
