Blinded by the Light, 2020

“If glass is the answer what was the question?” (Ian Ritchie, 1998)

Although we think of glass as transparent, which it is when viewed from the darker side of the glass, and noticeably when viewed externally in daylight, glass is most often experienced as an opaque surface; it only becomes transparent as the viewing angle becomes more perpendicular to its surface. Glass is thus generally dark in daytime (unless reflecting the sun) and at night, when lit internally, it mostly displays the building’s lighting fixtures, making its automatic default use for complete facades questionable. For the Sainsbury Wellcome Centre in London our office did consider the potential glare from the low evening sun, and mitigated this by ribbing and undulating the cast glass surface.

Architectural features that would cause undesirable reflections are best eliminated early in the design process before modification to the building’s form and facade become impossible. Failing that, there are several approaches to prevent or mitigate glare in highly specular building facades whose geometry and glazing have created unwelcome reflections.

Mitigation Methods

Shading

External blinds and screens, such the Middle Eastern mashrabiya, metal mesh and perforated screens as a second skin to the façade, fixed or mobile, break up the sun’s rays that enter or reflect off a building by intercepting them before they reach the facade. For east and west facing facades, increasing the depth of the mullion or structural element can create sufficient interruption of sunrays. They must be installed outside the thermally insulating glazed surface in order to be effective. Blinds installed between the thermal barrier glazed wall and an outer single glazed ventilated glass skin (The Cheesegrater and the Shard) only address solar gain, and do not mitigate glare.

Brise Soleil

This was popularised by Le Corbusier, this and is most commonly used to prevent facades with a large amount of glass from overheating during the summer, and It typically consists of a horizontal projection extending from the sunside facade of a building.

Anti-Reflective Glass

Advancements in glass manufacturing promising new ways of reducing glare include advanced ‘high performance’ anti reflective coatings. The benefits of using anti-reflective glass include maintaining greater transparency across the facade.

Post-Construction Modification of the Reflective Surface

The method used depends whether the material is glass or metal. The problem of the stainless steel surface of the Walt Disney Concert Hall was solved by hand-sanding the offending areas to a dull finish to diffuse the reflections.

Window films and anti-reflective coatings can be applied post-construction to mitigate problem reflections. However, reduction of reflected light leads to an increase in the amount of solar energy absorbed, increasing the building’s solar gain, which generates its own problems. Another issue is that such coatings have a limited lifespan and may need manual removal and reapplication at regular intervals.

Retrofitted measures to mitigate unwanted facade reflections are by necessity lo-tech. By considering which design features are most likely to increase the potential for issues relating to reflections, and avoiding them, and understanding the basic physics of reflection, architects should be able to greatly reduce the chances of these issues from occurring. In terms of facade materials used, specular facades are most commonly the source of urban glare and in that context glazing is both the most common source of, and a potential solution to, the problem.