Glare is a visual sensation caused by an uncontrolled light far brighter (2) than its surroundings creating an excessive range of luminance in the eye’s field, or because there is simply too much light over all. It is divided into two categories: Disability Glare which impairs vision, and Discomfort Glare which is annoying and causes eyestrain.
“Light is the opium of the architect and shadow its form.” (Ian Ritchie, 2002)
The refraction of light gives the human eye its sense of vision. Light as we use it in architecture is perceived not directly, but through reflecting surfaces. Sunlight allows space and form of architecture to change. Through light and shadow architecture acquires shape and meaning. Light reveals a building’s contours and shadow, its depth.
The range of light perception by the human eye (3) is from about 0.001 lux – in black space/ night sky – to 100,000 lux – bright sunlight. But eyes need time to adapt (4), so sudden glare is potentially dangerous for the aircraft pilot, a vehicle driver at night, the train driver trying to read coloured signals, and for the pedestrian or driver in a city of glass towers.
Architects clearly delight in the play of light and play with light, reflected and refracted, both inside and outside buildings. In large modern cities, characterised by tall buildings with ever more geometrically complex and reflective facades, the interplay of multiple reflection and refraction, light and shadow, from and between buildings, can become as mathematically complex as it is visually beautiful. It is important to remember that members of the public also often find beauty in the reflective facades of urban architecture. Some of the acclaimed artist Brendan Neiland’s work – paintings of reflections in the glass and mirrored architecture of the 21st-century city reveals the dynamic of this living, shifting, visual architectural intricacy, a subject that John Cage, writer and composer, also found enchanting.
The same light that delights the eye can also blind or burn when concentrated and reflected from highly reflective glass or metal, as Archimedes, who is said to have used parabolic reflectors during the Siege of Syracuse to set fire to approaching Roman ships, was well aware. Architects intoxicated by the visual delight of the shapes and forms they are designing often neglect to consider the potential negative impacts of highly specular facade surfaces, including the reflective coatings used on glass to reduce solar gain and glare inside buildings by reflecting it as heat and glare into nearby public spaces and buildings.
Do architects consider glare and the potentially dangerous and annoying impact that reflected light can have on pedestrians, car drivers, adjacent properties and their occupants when designing buildings wrapped in glass or shiny metal? Over the last thirty-odd years there have been many examples indicating they seldom do. If not, why not?
I suspect that most do not bother with such considerations or analysis because there has been no statutory requirement or, for that matter, any common understanding of what amount of candela would define glare, though most would accept that looking into the sun would qualify, or scientific agreement on the amount of difference between a bright light and its surroundings which would constitute glare.
Architects do take into consideration the shadows cast by their buildings because of neighbouring properties’ Rights to Light and Sunlight/Daylight criteria, for which most countries have regulations, and because the precisely calculated play of shadow can enhance architectural forms.
Several high-profile buildings designed by well-known architects during the last decade have caused discomfort and damage due to irradiance and concentrations of thermal and visual glare. Popularly known as ‘fryscrapers’ or ‘death ray buildings’, these buildings caught the imagination of the press and public, creating a growing realisation in the architectural and planning community of the potentially severe consequences of uncontrolled solar reflections from the built environment and of the need to assess and mitigate glare in architectural facades.
An example is Frank Gehry’s Walt Disney Concert Hall in Los Angeles. Shortly after opening in 2003, surrounding residents and businesses complained of blinding glare as well as increased indoor temperatures. The surfaces of nearby sidewalks reached up to 60C and visual glare disrupted surrounding traffic intersections. Officials at Gehry’s firm insisted that they had taken possible glare into account, but that curved panels were erected at slightly different angles than called for in their design. Gehry did not seem to have remembered that his design for the Weisman Art Museum (1993) on the Minnesota University campus was criticised for the glare it created for drivers facing its west façade when crossing the Washington Avenue Bridge.
In 2010 it was discovered that the reflective surface and concave design of the Vdara Hotel in Las Vegas, by Rafael Vinoly, which had opened the year before, could act as a collecting mirror which focussed the sun’s rays onto the pool deck below, creating temperatures high enough to scorch hair and burn skin.
In Dallas, the 42-story Museum Tower, designed by Scott Johnson and completed in 2013, reflects such intense light into the neighbouring Nasher Sculpture Center, designed by Renzo Piano, that within two weeks of installation of the Museum Tower’s mirrored curtain wall, the Nasher’s bamboo plantings were killed off by scorching. The reflections also so altered the precisely calibrated solar conditions within the gallery that artworks were threatened, and the light artist James Turrell requested that the Nasher remove his permanent installation there as it had been “destroyed”.
The Sculpture Center has been left to mitigate the glare with internal blinds, leaving inadequate and unattractive lighting conditions for the art.
Designed by Rafael Vinoly in 2005-6 (at probably the same time as Vdara Hotel), and completed in 2014-15, ‘20 Fenchurch Street’ in London – a.k.a. ‘the Walkie-Talkie’, hit press headlines even before it was completed. The concave/parabolic surface of the facade reflected and concentrated beams of sunlight onto parts of the pavement, which reached temperatures in excess of 100 deg. C. The heat melted plastic parts of a motorist’s parked Jaguar, burnt carpets and melted plastic bottles in nearby shops, and incidentally created daily street theatre as crowds gathered to watch eggs being fried on the sidewalk. Vinoly predicted reflections but – apparently in conversation with the Guardian – said, “There was a lack of tools or software that could be used to analyse the problem accurately.”
Renzo Piano’s design of the elegant ‘Shard’ in London, which opened in 2013, was beset by numerous problems of reflection, inside and out, both during daylight hours and at night. Reflections from the facade dazzled train drivers on the south-eastern train tracks leading to the London Bridge Terminal. Internally, embarrassed visitors complained that reflective glass in the loos bounced reflections off ceiling and walls and into and out of other cubicles. At night, guests of the Shard’s Shangri-La Hotel were able to see into each others’ rooms when glass panels protruding from the building’s corners acted as mirrors once internal lights were switched on at night.
Visual (not thermal) glare is not restricted to daylight. London’s Crossrail has lodged a formal objection against the proposed MSG Sphere in Stratford, east London, warning that giant LED advertising screens on the 90m-tall entertainment venue would compromise safety by impairing train drivers’ ability to pick out signals vital for running high speed trains on a complex part of the network. It is feared the effect, called masking, would occur because the luminance of the glaring LED screens behind signals at the side of the tracks would be several orders of magnitude greater than the luminance of the signals.
Whereas there is still no internationally accepted methodology to demonstrate glare from reflective facades, methods exist which can be used to estimate the sensation of glare to which passing motorists and pedestrians would be subject, such as the Hassall method as described in his book Reflectivity (5). When designing for network Rail 20 years ago, my practice was made fully aware of the dangers of glare for train drivers, and we were obliged to demonstrate that solar reflections would not diminish a driver’s ability to see the colour of signals.
Accurately calculating glare is still problematic, although David Hassall’s book Reflectivity was published in 1991 with glare templates. The first glare-related legislation, one suspects because of that publication and lobbying, was adopted by Sydney City Council in 1992: ‘Veiling luminance’ suggested a maximum reflected solar glare of 500 candelas (cd) /m2 on vehicle drivers. Later, the same council limited the exterior surface reflectivity of a building to 20%, specifying that all materials including window glass will have a reflectivity below 20%. Singapore and Rotterdam have adopted similar legislation. The City of London brought in a Planning Advice Note on the subject in 2017, with reference to a BRE Information Paper IP 3/87 ‘Solar dazzle reflected from sloping glazed facades’ (IHS BRE Press, Bracknell, 1987) on how to carry out the calculations.
Obviously glare should be considered when contemplating the massing of a building or a larger development. This requires evaluating the geometries and surfaces of neighbouring buildings with specular facades, potential secondary and tertiary reflections, the Earth’s movement in relation to the sun, local topography, viewing points, and types of public and transport spaces.
This brings immediate awareness of the basic laws of optical physics: angle of incidence equals angle of reflection, and the trajectory of nature’s own laser – the sun. Such calculations, including sciagraphy used to determine the perspective projection of shadows suggest immediately that a concave surface will focus light, and a convex surface will scatter it, though still potentially create moments of glare. During the design process of any structure it would seem sensible to avoid surface geometries – particularly parabolic and multiple-angled – that could focus sunlight to cause glare and overheating.
Intelligent building orientation and facade design can clearly mitigate glare, and limiting a building envelope’s reflectivity to prevent glare might be considered a banal approach when it is clearly possible for an architect or technical advisors to demonstrate the level of risk using sun-path analysis of a reflective façade. In interior lighting, good design practice either diffuses the light to reduce the luminance or shields the source from view. There is no reason the same practice should not be applied to reflected sunlight.
“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.
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.
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.
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.
(1) Disability Glare is the reduction in visibility caused by intense light sources in the field of view. Discomfort Glare is the sensation of annoyance or even pain induced by overly bright sources (Rea 2000).
(2) The word brightness is commonly used but is technically incorrect. It is luminance and is measured in candelas/square metre.
(3) There are considered three different vision regimes. Photopic vision relates to human vision at high ambient light levels (e.g. daylight) and applies to luminance levels > 3 cd/m2. Scotopic vision relates to human vision at low ambient light levels (e.g. night) but the sense of colour is largely lost – seeing a range of gray light, and applies to luminance levels < 0.003 cd/m2. Mesopic vision relates to light levels between the photopic and scotopic visions.
(4) The artist James Turrell exploits this fact in most of his work on the limits of visual perception.
(5) ‘Reflectivity: dealing with rogue solar reflections’ by David N.H. Hassall, 1991, Building Research Centre, School of Building, University of New South Wales
This article was originally published in IGS Magazines Summer 2020 USA Special Edition: Read the full Magazine here for more thought-leadership from those spearheading the industry
Author: Ian Ritchie, Founder of Ian Ritchie Architects
In 1981 Ian Ritchie established his own architectural practice – Ian Ritchie Architects Ltd. (iRAL) and co-founded Rice Francis Ritchie (RFR) a design engineering practice in Paris – with Peter Rice and Martin Francis. RFR did seminal work on glass and fabric structures during the 80s on the Museum of Science, Technology and Industry at La Villette, and the Louvre – pyramids and sculpture courts.
By the 1990s iRAL had become world-renowned for their glass architecture, material-technical innovation and intelligent environmental and sustainable design – of which iRAL’s most recent major projects, the Sainsbury Wellcome Centre for Neural Circuits and Behaviour (2016), and Royal Academy of Music Theatre and Recital Hall in London, (2018) are an evolution. iRAL has won over 60 competitions in Europe and the UK and received over 100 national and international awards.