Glare metric, not a room-size result
UGR means Unified Glare Rating. It is an indoor discomfort-glare metric used in lighting discussions. It is not a brightness unit, lamp output value, wattage figure, colour-quality score or simple whole-room label.
UGR belongs to the relationship between the observer, the luminaires and the surrounding field of view. A luminaire can be comfortable from one desk and distracting from another. A room can have enough lux on the workplane while still producing discomfort from exposed bright sources, poor shielding, unsuitable spacing, screen reflections or high contrast.
The UGR glossary entry gives the compact definition. For a lighting note, the key point is narrower: UGR needs observer and photometric evidence, not room area and lumens alone.
Choose the glare check
UGR searches often begin after someone notices a harsh room, a screen reflection or a bright fitting in the normal view. The first job is to separate discomfort glare from low illuminance, colour quality, reflected glare and ordinary fitting data.
| User question | Note to settle first | Page that carries the work |
|---|---|---|
| What does UGR mean? | Observer position, viewing direction, luminaire data and indoor discomfort-glare context. | UGR glossary entry |
| Is the room too dark instead? | Measured lux on the task plane, target basis, control state and maintenance condition. | Lux meter reading notes |
| Is the issue a reflected source? | Screen angle, glossy surface, window or luminaire position and the observer view. | Glare definition |
| Is the luminaire data enough for glare modelling? | Photometric file, diffuser, output setting, mounting height and exact set-out. | Luminaire markings table |
| Do finishes or daylight change the complaint? | Ceiling, wall, floor and furniture reflectance with daylight and dimming condition. | Surface reflectance planning table |
| Is it a workplace lighting note? | Task area, furniture layout, observer positions, maintained-light basis and document boundary. | Office lighting guide |
What UGR describes
UGR describes likely discomfort glare from luminaires in an indoor visual scene. It is mainly discussed for offices, classrooms, workrooms, reception areas and other interiors where people look across a space while reading, typing, inspecting, teaching, presenting or moving through a work area.
The number is normally produced from a lighting design model, photometric files and nominated observer positions. The result depends on what the observer sees: source luminance, apparent source size, source position in the field of view and background brightness.
| UGR depends on | Evidence needed | Why room area is not enough |
|---|---|---|
| Observer position | Seated or standing viewpoints. | Glare changes when the viewer moves. |
| Viewing direction | Screen direction, teaching wall, workbench direction or circulation view. | A bright source may be visible in one direction and outside the main view in another. |
| Luminaire luminance | Photometric data, diffuser and optic details. | Total lumens do not describe visible source brightness. |
| Source size and angle | Apparent source area and position in the field of view. | Ceiling plan geometry affects discomfort. |
| Background luminance | Room surfaces, finishes and daylight condition. | Contrast changes the glare reading. |
Why a room-size shortcut would be misleading
Simple room inputs can support rough illuminance estimates. Length, width, target lux, utilisation factor, maintenance factor and luminaire output can estimate required lumens or average maintained lux. UGR is different.
UGR depends on luminance, observer position, background luminance, solid angle, luminaire direction, mounting height, spacing, shielding, room surface reflectance and the photometric distribution of the actual luminaire. It also depends on viewing direction. Changing desk orientation or observer position can change the glare assessment even when the room dimensions, fitting count and total lumens stay the same.
| Simple input | Valuable for lux/lumen estimates | Missing for UGR |
|---|---|---|
| Room length and width | Defines assessed area. | Observer view and source position in the visual field. |
| Ceiling height | Helps estimate mounting geometry. | Visible source luminance and shielding. |
| Lumens per fitting | Supports output and count estimates. | Luminance distribution and apparent source size. |
| Fitting count | Supports installed lumens and connected load. | Exact set-out relative to observer positions. |
| Target lux | Identifies illuminance intent. | Discomfort-glare threshold and visual scene modelling. |
A UGR value generated from room length, room width, ceiling height and lumens per fitting would look precise while leaving out the data that controls glare.
Australian workplace context
In Australia, UGR is most relevant in interior and workplace lighting discussions rather than ordinary household lumen estimates. The AS/NZS 1680 series is the usual Australian/New Zealand context for interior and workplace lighting principles, recommendations and application-specific guidance. For offices, the glare discussion sits beside task illuminance, uniformity, screen-based work, surface brightness, daylight, luminaire selection and layout.
Safe Work Australia also treats lighting as part of the workplace environment. Its guidance discusses lighting, glare, contrast and reflections as practical conditions that can affect visual strain.
For workplace, education, healthcare, public-building or emergency-related work, the lighting note should identify the applicable document, task area, design method, luminaire data, maintained-illuminance basis and responsible reviewer. Adjacent context is in the office lighting guide, the workplace lighting calculator and lux levels for Australia.
Evidence to collect before discussing glare
A useful glare note begins with evidence. Without it, UGR becomes a decorative number in a schedule rather than a design check.
| Evidence item | Note | Why it belongs in the glare note |
|---|---|---|
| Room geometry | Length, width, ceiling height, bulkheads and suspended features. | Geometry sets the relationship between luminaires and observer positions. |
| Furniture and task layout | Desk rows, workbenches, screens, teaching walls, counters and circulation paths. | People do not view the room from a generic centre point. |
| Observer locations | Seated and standing positions representing normal work. | UGR is calculated from nominated viewpoints. |
| Viewing directions | Main sightlines, screen orientation and presentation walls. | The same luminaire can be visible or irrelevant depending on direction. |
| Luminaire data | Exact model, output setting, optic, diffuser, photometric file and mounting detail. | UGR needs luminance and distribution data, not only a fitting name. |
| Surface finishes | Ceiling, wall, floor and large furniture reflectance or colour. | Background luminance affects perceived contrast. |
| Field observations | Complaints, photos, measured lux and screen reflections where the room exists. | Existing evidence helps separate glare, low lux and reflection issues. |
The luminaire markings table separates lm, W, K, CRI/Ra, IP and dimming statements so glare evidence is not confused with ordinary fitting markings. The surface reflectance planning table and lighting control notes table help keep background brightness, daylight-affected rows and dimmed scenes out of a single generic glare note.
Field note before a glare conclusion
For an existing room, a glare note should separate measured light, visible sources and surface contrast. That keeps UGR language from being used as a label for every visual complaint.
| Field note | What to capture | Related page |
|---|---|---|
| Measured task plane | Lux readings at the desk, bench, board or circulation surface. | Lux meter reading notes |
| Measured term | Whether the value is a field reading, estimated value or maintained design basis. | Measured illuminance |
| Glare type | Direct source, reflected source, screen reflection, window contrast or outdoor spill. | Glare |
| Surface condition | Bright ceiling, glossy desk, dark wall, glass, screen or pale floor. | Surface reflectance planning table |
| Control state | Full output, dimmed scene, daylight row, after-hours group or presentation mode. | Lighting control notes |
If the room feels harsh only under one scene or at one desk direction, the note should name that condition. The same layout can feel different after a blind setting changes, a perimeter row dims, a screen turns toward a window or a bright luminaire enters the normal line of sight.
Separating glare from low light and reflections
Not every visual complaint is a UGR problem. A desk can feel uncomfortable because the task plane is underlit, because a glossy screen reflects a window, because a fitting is visible in the main line of sight or because dark finishes create strong contrast.
| Symptom in the room | Likely evidence to check | Related lighting term |
|---|---|---|
| Area feels dim. | Measured lux across the task plane, target lux and maintenance condition. | Lux and maintained illuminance. |
| Bright source catches the eye. | Luminaire shielding, diffuser luminance, position and viewing direction. | Discomfort glare and UGR. |
| Screen shows bright reflections. | Screen angle, window position, luminaire position and glossy surfaces. | Reflected glare. |
| Room feels harsh despite enough lux. | Contrast, surface finishes, CCT, source size and ceiling brightness. | Adaptation and visual comfort. |
| Colours look flat but glare is not obvious. | CRI/Ra, CCT and surface material. | Colour rendering and colour temperature. |
Keeping those causes separate prevents a lux increase from being treated as the cure for every visual problem.
UGR is not lux, lumens, CRI, CCT or IP
Lighting notes often mix performance terms. Keeping them separate prevents false confidence.
| Term | Main question | Data source | Relationship to UGR |
|---|---|---|---|
| UGR | Will luminaires in the visual field cause discomfort glare? | Lighting model, observer position, photometric and layout data. | Indoor visual-comfort metric. |
| Lux | How much light reaches the assessed plane? | Calculation or lux meter reading. | A room can meet an illuminance target and still have glare. |
| Lumens | How much visible light leaves the luminaire? | Luminaire data sheet or marking. | Output contributes to the scene but does not define glare alone. |
| CRI or Ra | How naturally colours are rendered. | Colour data for the source. | Colour quality does not settle visible source brightness. |
| CCT | Whether white light appears warm, neutral or cool. | Kelvin marking or specification. | Cooler appearance is not the same as lower glare. |
| IP rating | Ingress protection against solids and water. | Luminaire marking. | Environmental protection does not indicate discomfort glare. |
For adjacent definitions, keep the CRI ratings table, colour temperature table, glare term and luminaire markings table beside the lighting schedule.
Practical note for offices and interior work
Treat UGR as a model-based glare discussion. For office and interior work, check whether the luminaire type, diffuser, mounting height, spacing, furniture layout and viewing directions suit the visual task. Keep glare beside maintained lux, uniformity, surface brightness, screen reflections, daylight control, colour quality and maintenance assumptions.
When a formal UGR assessment is required, the value should come from appropriate lighting design software or a lighting designer working with the actual photometric file and layout. The project note should keep the assumptions with the drawing or schedule: observer positions, viewing directions, luminaire data, surface reflectance, mounting details and calculation settings.
For general information boundaries, read the disclaimer. For room and workplace estimates around the glare discussion, see the office lighting guide, workplace lighting calculator, lux levels for Australia and lux meter reading notes.