UGR below 19: specifying low-glare linear lighting for offices and classrooms

Q: Is UGR a property of the light fixture?

Not on its own. UGR is calculated for an installation and an observer position. Manufacturers publish UGR values for standard rooms, which are useful for comparing fixtures, but the project's real value depends on its layout and surfaces.

Q: What UGR is required for offices?

UGR below 19 is a widely used recommendation for offices and classrooms (for example, in European standard EN 12464-1). North American practice often uses other glare metrics and luminance limits, but UGR is common in specifications.

Q: Do low-glare optics reduce efficiency?

Often a little. Optics that cut high-angle brightness (microprismatic lenses, louvres, deep regressed sources) usually absorb some light. Compare delivered lumens from the IES files, not only the UGR value.

Q: Does a diffuse opal lens guarantee low glare?

No. An opal lens hides the LED dots but can still be bright at high angles if the output per foot is high. Check the UGR table and the luminance.

Short answer

UGR (Unified Glare Rating) is a CIE method that rates discomfort glare for an observer in a specific room, on a scale of roughly 10 to 30 (lower is better). UGR below 19 is the usual target for offices, classrooms and other screen and reading work. UGR depends on the whole installation: room size, surface reflectances, mounting height, layout and viewing direction, not only the fixture. Manufacturers publish UGR tables for standard rooms; compare fixtures under the same conditions, and check the project layout with the IES file.

Key takeaways

UGR rates a room and a viewpoint, not just a luminaire.

UGR < 19 is the common target for offices and classrooms.

Compare published UGR tables at the same room size, reflectances and spacing.

Low-glare optics (microprismatic, louvre, deep regress) often trade some efficiency.

Direct/indirect suspended linear reduces contrast with the ceiling.

What UGR measures

The Unified Glare Rating, defined by the CIE, estimates discomfort glare: the annoyance caused by bright luminaires in the field of view. It combines the luminance of each luminaire as seen by an observer, its size and position in the view, and the background luminance of the room.

Limits are set in steps of 3. Typical limits used in specifications, following the examples in EN 12464-1:

UGR limit	Typical use
16	Technical drawing and very detailed visual work
19	Offices, classrooms, reading and writing
22	Industrial and craft work
25	Rough work
28	Corridors and circulation

Why the room matters

Because UGR depends on what an observer sees, the same fixture produces different values in different rooms. Glare goes up with:

higher output per fixture (more lumens per foot);
lower mounting height or longer rooms (more fixtures near the line of sight);
darker room surfaces (less background luminance);
viewing along the length of linear fixtures versus across them.

That is why a spec line reading “UGR<19” needs conditions: either a standard table reference, or a calculation for the actual layout.

How to compare linear fixtures

Use the manufacturer’s UGR table, usually given for standard room sizes and reflectances (often 70/50/20) and a spacing-to-height ratio.
Compare at the same conditions, same room, reflectances and spacing, and same output per foot.
Check delivered lumens from the IES file. A low UGR from a dim fixture does not help if you then need more fixtures.
Run the project layout in a lighting calculation when glare is critical.

Design choices that reduce glare

Choice	Effect	Trade-off
Microprismatic or low-glare lens	Cuts high-angle luminance	Some efficiency loss
Louvres / deep regress	Strong shielding	Visible hardware, cost
Direct/indirect suspended linear	Lights the ceiling, lowers contrast	Needs ceiling height
Lower output per foot, more rows	Lower luminance per fixture	More fixtures
Lighter room finishes	Raises background luminance	Architectural decision

For open offices and classrooms, suspended direct/indirect linear is a common way to get both low glare and a bright-feeling room. See suspended linear lighting. Recessed linear with low-glare optics suits lower ceilings; see recessed linear lighting.

Glare in substitutions

Glare is a frequent reason an alternate gets rejected: the same lumens, but a brighter lens. When proposing an alternate, include its UGR table at the same conditions as the basis of design. See or-equal substitutions.

How SuppLux helps

When a spec calls for low glare, put the UGR limit and its conditions on the schedule. Send the fixture schedule and SuppLux’s AI matches every line to verified products, with the best alternative shown first, then turns the matched set into a quote and submittal package. Send a schedule.

Frequently asked questions

Is UGR a property of the light fixture?

Not on its own. UGR is calculated for an installation and an observer position. Manufacturers publish UGR values for standard rooms, which are useful for comparing fixtures, but the project’s real value depends on its layout and surfaces.

What UGR is required for offices?