UGR: Are You Measuring the Right Thing?
The UGR value on your product data sheet and the UGR in your lighting design are not the same thing — and confusing the two can cost you a project, or a client’s trust.
Every professional in commercial lighting has heard the client ask: “What’s the UGR of this fixture?” And most of us have pointed to the spec sheet without hesitation. But here’s the uncomfortable truth most sales reps and even some designers gloss over:
The UGR printed on a product test report is not the UGR of the room. It’s a reference value calculated under controlled, standardized conditions — and it means something very different from the UGR you would model in a real space.
Let’s unpack both — what they are, how each is calculated, and why the distinction matters enormously when specifying for schools, offices, and healthcare spaces.
Fig. 1 — The CIE UGR formula. Each parameter is a function of the installation environment, not solely the product.
What the product test report actually gives you
When a manufacturer publishes a UGR value in a datasheet, they are using the tabular method defined in CIE 190:2010. The luminaire is tested in a standardized reference room — typically 4H × 8H or 2H × 4H in size — with fixed reflectance values (ceiling 0.7, walls 0.5, floor 0.2) and a fixed observer position.
The result is a UGR table: a matrix of values for various normalized room sizes and viewing directions. This table tells you how the luminaire performs optically — its luminous intensity distribution, its luminance at high angles — under controlled conditions. It is fundamentally a product characterization tool, not a room compliance certificate.
Reference room reflectances fixed: ρceiling = 0.70 / ρwall = 0.50 / ρfloor = 0.20
Observer positions: longitudinal and transverse, end and centre of room
Mounting height: normalized to H (floor-to-luminaire)
Fig. 2 — A typical UGR tabular output from photometric testing. Values vary by observer position and normalized room size. Reference room reflectances are always fixed per CIE 190.
What lighting design software actually calculates
When you run a DIALux or Relux simulation — or perform a manual UGR calculation for a specific project — you are calculating the room-specific UGR. Every parameter is now real: the actual room dimensions, the measured or specified surface reflectances, the exact mounting height, the number of luminaires, their positions, and the observer’s location in the space.
The result is what a person sitting at a workstation in your designed space would actually experience. This is the value that must comply with the EN 12464-1 or WELL standard requirement — not the datasheet number.
The same luminaire may produce UGR 19 in a small, low-ceiling corridor and UGR 14 in a large open-plan office with light-colored walls. The fixture didn’t change — the space did. Room geometry and surface reflectances can shift the UGR by 4 to 8 points in real-world projects.
UGR limits by application — EN 12464-1
| Space type | UGRL limit | Notes |
|---|---|---|
| Open-plan offices, reading rooms | 19 | Most commonly specified |
| Reception, lobbies | 22 | Higher tolerance acceptable |
| Technical drawing, precision work | 16 | Critical visual task environment |
| Classrooms, lecture halls | 19 | Includes display screen viewing direction |
| Hospital wards | 19 | Lying patient’s viewpoint is key |
| Industrial — fine assembly | 16 | Sustained visual demand |
| Corridors, circulation areas | 25 | Transient spaces, lower demand |
Fig. 3 — Product UGR (tabular method per CIE 190) versus room-specific UGR (design calculation). Both use the CIE formula, but the inputs — and therefore the answers — are entirely different.
So what should you actually specify?
When a client or consultant specifies “UGR < 19,” they need the room-specific simulation result — not just a product with a UGR table that shows some values below 19. As a supplier or manufacturer’s representative, the honest and correct response is:
“Our product has favorable photometric characteristics that support UGR < 19 in typical office conditions. Your lighting designer should verify this in simulation using our IES/LDT file for the specific room geometry.”
This protects you, educates the client, and builds long-term credibility — especially as EN 12464-1 and WELL v2 certification become standard requirements in the European and North American commercial market.
The bottom line: The UGR in a product test report is an optical fingerprint of the fixture. The UGR in a lighting design is a prediction of human visual comfort in a specific space. They use the same formula, but they answer entirely different questions. Knowing the difference — and being able to explain it clearly to a client — is what separates a lighting professional from a spec sheet reader.