UGR Value Explained: Glare Assessment in Interior Lighting
What Is the UGR Value?
The UGR value (Unified Glare Rating) is an internationally standardised metric for assessing psychological glare caused by a lighting installation in interiors. On a defined scale, it indicates how strongly a lighting setup is perceived as glaring. The lower the UGR value, the lower the glare.
The crucial point: the UGR value is not a property of an individual luminaire but describes the glare effect of an entire lighting situation. The calculation takes into account:
- The luminance of the luminaires (how bright the light-emitting surface appears)
- The size of the luminous area within the field of view
- The position of the luminaires relative to the observer's line of sight
- The background luminance (brightness of the surroundings, walls, ceiling)
- The room geometry (room size, ceiling height)
This means the same luminaire can produce a lower UGR value in a small room with light-coloured walls than in a large room with dark surfaces.
The UGR Scale
The UGR value is given in increments of three: 10, 13, 16, 19, 22, 25, 28. The assessment:
- UGR 10: Glare practically imperceptible
- UGR 13: Glare just perceptible
- UGR 16: Glare perceptible but still acceptable – limit for technical drawing and fine visual tasks
- UGR 19: Slight glare – limit for office and screen-based workstations, classrooms, medical practices
- UGR 22: Moderate glare – limit for industrial workplaces and workshops
- UGR 25: Noticeable glare – limit for general industrial halls and warehouses
- UGR 28: Strong glare – only acceptable for coarse visual tasks
UGR Limits According to DIN EN 12464-1
The European standard DIN EN 12464-1 (Lighting of Indoor Workplaces) defines maximum UGR values for various activities and room areas:
- UGR ≤ 16: Technical drawing, CAD workstations, precision mechanical work
- UGR ≤ 19: Offices, screen-based workstations, classrooms, medical practices, libraries, conference rooms
- UGR ≤ 22: Workshops, production halls with moderate visual tasks, retail spaces
- UGR ≤ 25: Industrial halls, warehouses, coarse assembly work
- UGR ≤ 28: Corridors, stairwells, circulation areas
There are no normative UGR requirements for residential spaces, but glare-free light is equally important for visual comfort in the home.
How Is the UGR Value Determined?
The UGR value is determined by calculation – direct measurement in a completed room is complex and uncommon in practice. The standard methods:
- Lighting Design Software: Programs such as DIALux or Relux calculate the UGR value for a planned lighting situation based on the room geometry, surface reflectance values and luminaire luminances. This is the standard method in professional lighting design.
- UGR Table Method: Luminaire manufacturers supply UGR tables for their luminaires, showing the UGR value as a function of room size and reflectance values. These tables serve as a quick guide.
- Observer Position: The UGR value is always calculated for a defined observer position and viewing direction – typically seated (1.2 m eye height) with a horizontal line of sight.
What Does "UGR < 19" Mean for a Luminaire?
Many luminaire manufacturers advertise the specification "UGR < 19". This should be interpreted with care: since the UGR value depends on the entire lighting situation, a single luminaire cannot have a fixed UGR value. The manufacturer's specification refers to a reference room scenario – in practice, the actual UGR value may differ depending on room size, surface colours and luminaire arrangement.
Reputable manufacturers therefore supply UGR tables that account for various room sizes and reflectance values. In professional lighting design, the UGR value is always calculated on a project-specific basis using planning software.
Why Is the UGR Value Particularly Relevant for LED Luminaires?
LED luminaires generate light from very small, point-like light sources with high luminance. Without suitable glare control measures, this concentrated brightness can cause greater glare than the broadly emitting light of conventional fluorescent lamps. Premium LED luminaires therefore employ:
- Micro-prismatic optics that diffuse the light and reduce luminance
- Deep-set reflectors that prevent direct sight of the light source
- Recessed or set-back LED modules that are not directly visible
- Diffuse covers with high light transmission and low luminance
These measures lower the UGR value and ensure visual comfort – particularly important at screen-based workstations, where glaring luminaires can additionally cause reflections on the monitor.
Frequently Asked Questions (FAQ)
What is a good UGR value?
For offices and screen-based workstations, UGR ≤ 19 is the standard. For fine visual tasks such as technical drawing, UGR ≤ 16 is recommended. In residential spaces there is no standard, but a low UGR value delivers noticeably more comfortable light.
Can I measure the UGR value of an existing lighting installation?
Direct measurement is possible but complex and requires specialist measuring equipment (luminance cameras). In practice, the UGR value is determined by calculation using planning software.
Is it enough to buy luminaires rated "UGR < 19"?
The luminaire alone does not guarantee a UGR ≤ 19 in the room. The actual UGR value depends on the entire lighting situation – room size, luminaire arrangement, surface colours and viewing direction. Luminaires with a low UGR table value are a good starting point, but for standards-compliant lighting, professional lighting design is recommended.
What is the difference between UGR and glare control?
The UGR value is the measurable metric. Glare control refers to the structural measures in the luminaire (reflectors, louvre grilles, optics) that lower the UGR value. Further details can be found in the glossary article Glare Control Explained.
In Summary:
The UGR value is the key metric for glare-free interior lighting. It describes not the property of an individual luminaire but the glare effect of the entire lighting situation. For standards-compliant office lighting, UGR ≤ 19 is the benchmark. In professional lighting design, the UGR value is calculated on a project-specific basis – the team at Leuchtenland.com is happy to assist you in planning glare-free lighting solutions.