The glare generated by west-facing windows constitutes a distinct problem from other solar exposures. At the end of the day, the sun reaches low elevation angles, below 30° depending on latitude and season, before disappearing behind the horizon. At these grazing incidences, rays penetrate horizontally into rooms, bypassing most protective devices dimensioned for zenithal solar gains. The resulting visual discomfort is direct, recurrent and difficult to mitigate without completely blocking the opening.
A Specific Angle of Incidence for West-Facing Facades
Solar geometry explains the particular intensity of glare on west-facing facades. At low elevation, the sun sits within the direct field of vision of occupants positioned facing windows, particularly in offices, remote working spaces and living rooms. Incident rays then penetrate deep into rooms, horizontally illuminating work surfaces, screens and reflective surfaces. Unlike south-facing facades, where fixed protections (roof overhangs, solar canopies) can intercept radiation at high elevation, west-facing facades require protection adapted to low angles of incidence, precisely those for which fixed shutters and sun breakers perform least effectively.
Visual comfort in this context is assessed by two standardised indices in the field of building performance: DGP (Daylight Glare Probability) and UGR (Unified Glare Rating). These indicators take into account the luminance of the glare source, its position in the visual field and the ambient brightness level. A west-facing window in the late afternoon typically generates DGP or UGR values exceeding the comfort thresholds accepted in workspaces, without the overall brightness of the room being excessively high.
Why Blackout Solutions Remain Insufficient
Interior blinds or roller shutters provide an immediate but non-selective response: they suppress glare at the cost of complete blackout, forcing occupants to resort to artificial lighting in the middle of the afternoon.
Standard tinted glazing presents another structural limitation: its attenuation of visible light transmission (VLT) is constant throughout the entire solar cycle. A west-facing facade covered with tinted glazing will indiscriminately reduce morning and evening light, without correlation to the actual position of the sun. Natural light loss is significant throughout the entire day, without the specific evening discomfort being genuinely controlled.
The Solar Screen article dedicated to visual comfort against solar glare and anti-glare adhesive films (https://solarscreen.eu/en/blog/films-anti-eblouissement/) addresses the mechanisms of eye fatigue associated with excess brightness on glazing.
Spectral Selectivity as a Technical Response
High spectral selectivity solar films are based on a multilayer architecture allowing the wavelengths of solar radiation to be treated differently. The visible light component (380–780 nm) is transmitted in a high proportion, while near-infrared radiation, responsible for most thermal gains, is reflected or absorbed by the film. This spectral discrimination allows a high VLT to be maintained while reducing incident solar energy.
Glare reduction is achieved not through overall darkening, but by attenuating the luminance contrast between the glazed surface and the interior environment of the room. For a west-facing window, this approach preserves the benefit of natural light in the morning and through mid-afternoon, while attenuating visual discomfort in the two to three hours before sunset.
What Visible Light Transmission Level for Each Use?
Choosing a film reference for west-facing windows requires adjusting VLT to the requirements of each use:
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Workspace or office: a VLT between 55% and 70% reduces reflections on screens and eye fatigue without requiring additional artificial lighting during the day.
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Living room or lounge: a VLT around 65–75% preserves ambient brightness, an essential condition in living spaces where partial blackout would be poorly received.
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Bedroom: depending on privacy and thermal comfort needs, a lower VLT (40–55%) may be considered, particularly in regions with strong summer sunlight.
The selectivity of a film, defined by the ratio between its VLT and its overall solar factor (g-value), constitutes the key performance indicator for assessing its suitability for a west-facing exposure.
A Permanent Solution Without Architectural Modification
Unlike mobile devices, a solar film applied to glazing does not interfere with the operation of the opening and does not significantly modify the external appearance of the facade. Its installation is permanent and its performance remains stable over time with minimal maintenance.
The range of transparent solar films with high spectral selectivity (https://solarscreen.eu/en/range/solar-control/transparent/) from Solar Screen includes exterior references designed for glazing subject to significant direct solar gains. These films present a VLT that can exceed 70% for a total solar energy rejection above 55%, positioning them as relevant solutions for west-facing facades in residential or tertiary use. Their compatibility with double glazing and Low-E glazing must be verified in advance through a thermal stress analysis carried out by a qualified installer.