Glare occurs when bright sources, reflections or windows interfere with comfortable or effective vision. It is not defined simply by high illuminance, because the effect depends on the brightness, size and position of the source, the surrounding visual field and the direction in which a person is looking.
Discomfort glare is a sensation of visual annoyance, strain or unease caused by a bright source within the field of view. A person may still be able to see the task, but the visual environment can become tiring or distracting, particularly during prolonged work.
The response to discomfort glare varies between people and situations. A luminaire that causes little concern during brief movement through a room may become intrusive when it remains above or in front of a fixed workstation throughout the working day. The same source may also be experienced differently as the observer changes position.
Disability glare is a reduction in the ability to see caused by light scattered within the eye. The scattered light forms a veil over the retinal image, reducing the visibility of detail and contrast. It may occur without a strong sensation of discomfort, meaning that a person may not describe the condition as unpleasant even though visual performance has been impaired.
The distinction matters because the two forms of glare require different interpretation. Discomfort glare is associated with visual experience and acceptance, while disability glare concerns the loss of visual information. A bright source can produce either effect or both, depending on its position, intensity and relationship to the task.
The Unified Glare Rating, commonly referred to as UGR, is a method for estimating discomfort glare from electric luminaires in an indoor lighting installation. It developed from work by the International Commission on Illumination and provides a common design framework for comparing the likely glare effect of different luminaire arrangements.
UGR models the combined influence of visible luminaires within an observer's field of view. It considers the luminance of each luminaire, the apparent size or solid angle of that luminaire, the background luminance of the space and the position of the source relative to the observer's line of sight.
Luminaire luminance describes how bright the visible luminous part of the fitting appears in a particular direction. Solid angle represents how large that source appears from the observer's position. A large luminous surface may therefore contribute differently from a smaller source, even where both produce similar illuminance on the working plane.
Background luminance affects how strongly the source stands out from the surrounding visual field. A bright luminaire seen against a relatively dark ceiling or room background is likely to appear more prominent than the same luminaire within a brighter setting. UGR combines these factors into a design index rather than treating any one of them as the sole cause of glare.
UGR is dependent on where the observer is located and where that person is looking. A luminaire directly ahead or close to the normal line of sight generally contributes more strongly than a similar luminaire positioned farther to the side or behind the observer.
This makes workstation orientation important. Two desks beneath the same lighting installation can produce different glare conditions when one user faces along the luminaire rows and another faces across them. A rearrangement of desks, machinery or control stations can therefore change the experience of glare without any change to the luminaires.
The viewing direction should represent the activity rather than an arbitrary position selected for convenience. In an office it may be the direction of a display screen or document holder. In a control room it may be the main instrument panel, while in a workshop it may be the normal direction of attention towards a machine or bench.
A glare assessment should also consider whether people frequently turn or look upwards during the task. A fitting outside the primary viewing direction may become prominent during normal head movement, communication with colleagues or access to shelves and displays.
UGR is calculated from information about the room, the luminaires and the observer. The calculation normally requires luminaire photometric data, the geometry of the installation, surface properties, mounting positions and defined viewing directions.
A lux meter cannot directly measure UGR. It measures illuminance falling on its sensor, whereas UGR depends largely on the apparent luminance, size and location of visible sources within a particular field of view. A satisfactory illuminance reading at a desk does not establish that the luminaires above or ahead are visually comfortable.
A site survey can identify likely glare sources, observer positions, reflections and changes from the original design. However, reproducing a formal UGR calculation may require the design model and photometric files for the installed luminaires. Where the actual product, optical distribution or room arrangement differs from the model, the original calculation may no longer represent the occupied space.
Photography can help document the observer's view but does not by itself provide a reliable glare rating. Camera exposure, lens characteristics and image processing can alter the apparent brightness and size of a source. Visual records are therefore supporting evidence rather than a substitute for calculation and informed observation.
Glare may reach the eye directly from a luminaire or indirectly after reflection from a surface. Reflected glare is common on display screens, glass, polished stone, glossy worktops, coated paper, metal components and other surfaces with a directional reflection.
A veiling reflection is a reflected image or bright patch that lies over information or detail on the task. It reduces the visible difference between the feature and its background, making text, markings or surface defects harder to distinguish. Increasing the illuminance may not solve the problem and can strengthen the reflection if the geometry remains unchanged.
The position of the light source, the task surface and the observer determines whether a reflection enters the viewing direction. Tilting a screen, rotating a bench or moving a luminaire can alter this geometry. A small positional change may be more effective than increasing output or replacing the entire lighting system.
Screens present a particular challenge because their glossy or semi-gloss surfaces can reflect ceiling luminaires and windows. A person may respond by changing posture, leaning forward or repositioning the head to avoid the reflection. Prolonged awkward posture should not be treated as an acceptable method of glare control.
Polished materials used for inspection can also produce confusing highlights. Directional lighting may reveal certain surface features while concealing others beneath a strong reflection. The appropriate arrangement depends on the defect, texture or shape being examined and should be assessed from the normal observation position.
Windows can become significant glare sources when they contain bright sky, direct sun or strongly illuminated external surfaces. The problem can change during the day and across the year as the sun position, cloud cover and external reflectance change.
Daylight glare is influenced by window size, orientation, view direction and the contrast between the window and the internal setting. A window behind a screen may dominate the field of view, while a window behind the observer may create reflections on the screen or other glossy surfaces.
Control measures include repositioning the task, changing the viewing direction, shielding bright sources and selecting luminaires with suitable optical control. Diffusers can reduce the prominence of individual bright elements, although diffusion should not be assumed to remove glare in every arrangement. Louvres, baffles, shades and recessed light sources can limit direct view of high-brightness components.
Surface finish also affects the result. Matt finishes usually produce broader and less distinct reflections than polished finishes, while pale room surfaces can support a visually balanced background. Window blinds and shading devices can control daylight, but their position should preserve appropriate daylight and views where practicable rather than leaving them permanently closed.
In the Emirate of Abu Dhabi, the ADPHC Technical Guideline Ergonomics in an Office Environment covers glare control and task lighting and is classified by ADPHC as non-mandatory. At federal level, Article 4(c) of MOHRE Administrative Decision No. 19 of 2023 requires employers to avoid dazzle and glare in confined spaces.
In the Emirate of Abu Dhabi, workplace lighting is a mandatory matter. The Abu Dhabi Public Health Centre states that Codes of Practice under the ADOSH-SF framework are mandatory to all entities regardless of risk classification, and ADOSH-SF Code of Practice 8.0, General Workplace Amenities, Version 4.0, effective 15 July 2024, applies to all employers within the Emirate of Abu Dhabi. Its Section 3.8 sets minimum illumination intensities of 30, 10 and 5 foot-candles according to area type, which the Code itself converts at approximately 10.764 lux to the foot-candle. ADPHC's Technical Guideline on ergonomics in an office environment adds recommendations for office and screen work and is classified as non-mandatory. At federal level, MOHRE Administrative Decision No. 19 of 2023, Article 4(c), places lighting duties on employers within MOHRE's jurisdiction, including a requirement for emergency lighting when the primary system fails. EN 12464-1 and ISO/CIE 8995-1 are consensus standards: widely used and often specified contractually, but not statutory in the UAE unless an instrument adopts them. A requirement binding only in the Emirate of Abu Dhabi is not UAE law and must not be described as such.
ADOSH-SF Code of Practice 8.0 — General Workplace Amenities, V4.0 (15 July 2024), Section 3.8; MOHRE Administrative Decision No. 19 of 2023, Article 4(c)
No. Illuminance measures light falling on a surface, while glare depends on the apparent brightness, size and position of sources within the field of view. Glare can occur even where the measured illuminance is otherwise suitable.
Discomfort glare causes visual annoyance or unease. Disability glare reduces the ability to see by scattering light within the eye and lowering the visibility of detail.
No. A lux meter measures illuminance at the sensor. UGR is calculated from luminaire luminance, apparent source size, background conditions, room geometry and observer position.
The position of each luminaire relative to the observer's line of sight changes its contribution to discomfort glare. Turning a desk or changing the normal direction of attention can therefore alter the result.
Not necessarily. Additional light may intensify the reflection. Changing the position, angle, shielding or surface finish is often more relevant than increasing illuminance.
No. A diffuser can spread light and reduce the prominence of individual bright elements, but the resulting luminous surface may still appear bright or large from certain viewing positions.