UGR: glare in halls and offices and why UGR<21 matters

What the UGR value tells you

UGR stands for Unified Glare Rating, a CIE calculation method that expresses discomfort glare from indoor lighting as a single number. In practice the scale runs from 10 (barely perceptible) to 28 (disturbing). The lower, the less glare. A difference of 1 point is barely noticeable; 3 points is clearly felt. That is why the standards work in steps of 3: UGR 13, 16, 19, 22, 25 and 28.

Four things count in the calculation: the luminance (brightness) of each luminaire in the viewing direction, the size of the luminous surface as seen from the eye, the position relative to the line of sight, and the brightness of ceiling and walls. A small, bright point just above the line of sight scores badly; a large, evenly lit surface high in the ceiling scores well. UGR applies indoors only. Outdoors, on sites and sports pitches, the GR value is used.

Which UGR limit applies where

The workplace lighting standard EN 12464-1 links each task to an illuminance in lux and a maximum UGR. The most common combinations:

• Office work (writing, reading, screen work) and meeting rooms: 500 lux, UGR 19.
• Technical drawing: 750 lux, UGR 16.
• Reception desks: 300 lux, UGR 22.
• Archives and store rooms: 100 to 200 lux, UGR 25.
• Warehouses, dispatch and packing: 300 lux, UGR 25.
• Rough and medium machine work: 200 to 300 lux, UGR 25. Fine machine work: 500 lux, UGR 22.
• Corridors and circulation areas: 100 lux, UGR 28.

Sports halls fall under the separate sports lighting standard EN 12193, with roughly 200 to 750 lux depending on the sport and the level of play. Because players in ball sports often look straight up, low glare matters there at least as much as in an office. Note the difference: an installation that achieves UGR 22 in a hall is not yet good enough for an office with screens, where 19 is the limit.

Why a UFO high bay in a low hall quickly dazzles

A 100 W UFO high bay delivers 15,000 to 18,000 lumens from a luminous surface of roughly 30 centimetres across: a very bright source. At 10 or 12 metres that is no problem, the luminaire hangs well outside the normal viewing direction and looks small from the floor. At 5 or 6 metres, as in many workshops and sports halls, a forklift driver or order picker regularly looks straight at it. The UGR then easily exceeds 25.

A flat high bay spreads the same luminous flux over a much larger surface, behind an opal or microprismatic cover. The luminance per square centimetre drops sharply and the UGR with it. That is the difference between a luminaire that stands out and a hall that is simply well lit.

Flat high bays and light lines with UGR<21

For halls up to about 8 metres and for sports halls we offer flat LED high bays with UGR<21 in the ATRIA range. The 120 W version delivers 19,200 lumens (160 lm/W) with a 110° beam, is IP65 and IK10, 0-10V dimmable and carries a 5 year warranty. Above racking, the linear ATRIA high bay with 30x90° optics is the better fit: the beam falls into the aisle and not into the eyes of the driver in the next aisle. The UFO versions of ATRIA, up to 180 lm/W, remain the most efficient choice for high halls where the mounting height already limits glare.

For offices and retail, the LINEA light lines are designed for UGR<21: seamlessly linkable, in white or black, surface mounted or suspended, with adjustable output from 24 to 40 W. The optional indirect uplight module sends part of the light to the ceiling. That raises the background luminance, reduces the contrast with the luminaire and lowers the calculated UGR further.

Mounting height and optics: how you steer the UGR

As an installer you have more influence on the UGR than the choice of luminaire alone. The main levers:

• Mounting height: mounting higher shrinks the luminous surface for the eye and moves the luminaire out of the viewing direction. Below 6 metres, prefer flat or linear; above 8 metres a UFO is usually fine.
• Beam angle and optics: a narrower beam sends less light at shallow angles towards the eyes; a diffuse cover lowers the luminance of the luminous surface.
• Orientation: with light lines and linear luminaires the UGR lengthwise differs from the UGR crosswise. Run the lines parallel to the main viewing direction and check both values.
• Reflectance: a light ceiling and light walls raise the background luminance and lower the UGR. The same luminaires score worse in a dark hall.
• Eye height: the calculation places the eye at 1.2 metres for seated work. A forklift driver sits higher and looks up more often; include that position.

Luminaire UGR versus UGR in your project

The UGR on a datasheet is a table value from the CIE method for a standard room with reflectances of 70, 50 and 20 per cent for ceiling, walls and floor. Your hall or office always differs from that. The real UGR only follows from a lighting calculation with your dimensions, mounting height, luminaire layout and viewing positions. A luminaire with UGR<21 can exceed 22 in a low, dark hall and stay below 19 in a bright office with the right layout.

Lichtplein produces such a lighting calculation for 350 euros excl. VAT, with lux levels, uniformity and UGR per viewing position. From 100 luminaires we quote project prices. We supply businesses only, from European stock within 5 working days.

Frequently asked questions