In open-plan workspaces, glare is one of the leading causes of visual discomfort at the workstation. While standard NF EN 12464-1 (lighting for indoor work environments) is frequently applied to artificial light sources, it is rarely referenced in the context of glare caused by natural light entering through glazing. Yet daylight glare can reach luminance levels far exceeding those produced by LED panels, significantly contributing to eye strain and reduced productivity.
Reference Indicators for Glare Assessment
UGR (Unified Glare Rating)
The UGR is the standardised indicator for discomfort glare, defined by the CIE (International Commission on Illumination) and referenced in NF EN 12464-1. It is calculated from the luminance of the glare source, the background luminance in the room, and the observer's angular position relative to the source.
For screen-based workstations, NF EN 12464-1 sets a maximum UGR of 19 in office environments. Above this value, the risk of visual discomfort is considered significant.
In the context of solar glare through glazing, UGR is not always the most appropriate tool, as it was designed primarily for point sources. Glazed surfaces form extended high-luminance sources for which other indicators are more relevant.
Glazing Luminance and NF EN 12464-1
NF EN 12464-1 recommends that the luminance of glazed surfaces within the direct field of vision of occupants should not exceed 200 cd/m² in sensitive zones (screen-based workstations, precision tasks). In practice, sun-exposed glazing can reach luminance levels of 10,000 to 30,000 cd/m² — 50 to 150 times the recommended threshold.
Reducing glazing luminance is therefore the direct technical action required to achieve compliance.
DGP (Daylight Glare Probability)
The DGP is an indicator developed specifically for solar glare in buildings (Wienold & Christoffersen, 2006). It expresses the probability that an occupant will be disturbed by daylight glare. A DGP below 0.35 indicates an acceptable situation (fewer than 35% of occupants disturbed). Between 0.35 and 0.45, glare is perceptible. Above 0.45, it is unacceptable.
DGP is calculated from integrated luminance across the entire visual field and can be incorporated into natural lighting simulations (Daysim, Radiance, DIVA-for-Rhino).
Glazing-Side Solutions for Reducing Glare
Low Interior Reflection Solar Control Film
The most direct and least disruptive solution is applying a solar control film to the exposed glazing. The film reduces glazing luminance by absorbing and reflecting a portion of incident solar radiation, directly lowering the luminance perceived by occupants from inside.
For open-plan offices, neutral films with low interior reflectance are preferred: they minimise reflections on computer screens generated by the film surface itself. An interior reflectance below 10% is recommended for office spaces where the glazing is within the workstation field of view.
The advantage of film over blinds or curtains: it does not completely block the view to the outside (VLT is reduced but not eliminated) and operates permanently, with no daily manual adjustment required.
Selecting Products by Exposure
For open-plan offices facing east or west (low-angle glare in the morning or late afternoon), films with stronger luminance reduction (VLT of 40–55%) may be required. For north or south exposures with moderate glare, films with a VLT of 60–70% may suffice, preserving better natural light transmission.
Interaction with ISO 9241
ISO 9241-6 on ergonomic requirements for office work recommends limiting luminance contrasts in the operator's field of vision. Untreated glazing in the field of view can create a luminance ratio of 1:1,000 between the solar source and the screen surface — far exceeding recommended ratios (1:10 in the central field, 1:100 in the peripheral field).
Solar Screen anti-glare film, applied to the relevant glazed surfaces, can bring this ratio into compliance with the standard's recommendations, provided the correct product is selected based on exposure and the desired residual luminance level.
For a broader analysis, the dedicated article on choosing the right solar film for office spaces helps identify the most suitable products by exposure type.
To explore the neutral, low-interior-reflectance films available in the Solar Screen range, visit the solar control range for offices and commercial spaces.