Currently glass is one of the most used materials for facades in architecture. Some of the main reasons to use it, are the reduction of artificial light during the day and the creation of visual and thermal comfortable places to be. In this regard, many buildings seek to have a curtain wall system which cover all the façade with glass and allow them to maintain a high level of comfort in the interior. However when the interior have benefits the exterior may have some harm due to this material, and one of this is the glare effect. In this sense the following article describes the glare and its affects and how the architects can mitigate them.
As the Illumination engineering society of northern America (IES) consider, the glare is as a bright source that affects the ability to see, more specifically when the sensation of luminance is greater than the luminance that the eye is adapted causing annoyance, discomfort or loss of visual performance. The sources of glare can be direct or indirect. As direct we have the sun and a bulb, on the other side indirect sources can be either glass, smooth metal or any brushed surface.
The glare can have some effects on the viewers and these are classified in two. The first one is glare disability, this happens when the light interfere with the visual tasks due to the visibility reduction and the second one is the glare discomfort, which the light- effect not necessarily interfere the visual performance but the light received by the eyes is considered higher than the normal standards which produce a long term consequences.
The effects listed before can be stronger or lower depending on the following environmental factors. The first one is the direction of the light which manly is determined by the time of the day and the season. As an example during a normal day, in the morning the sun rays come from the east different from the afternoon where the light comes from the west. During summer the sun is higher, more vertical and the day last long, so the intensity of glare might be stronger for the viewers that are closed to the building and in winter the sun is lower more horizontal and the glare can affect the viewers located far from the building. Also if the viewer is looking directly at the source object the effect is really strong, this is common for people as motorcyclists or car drivers who drive along a highway and a building located in front of them can produce a glare enough to blind them.
Furthermore depend on the type of material, the glare effect can be higher or lower. To analyze them all materials have two types of reflections, the specular and the diffuse. The first one generates a mirror-like effect, this happens when the incoming light from the sun strikes the surface and reflect it with the same angle, and normally materials such as glass and brushed metal produce specular reflections. In contrast diffuse reflection scatter the light when this is reflected, their rough surfaces or matte finishes appear to glow, but it is very seldom that produce a glare effect.
Our concern now is to describe furthermore specular reflection because is the one that produce the glare but its effects depends on the shape of the surface. If we have a concave or convex surface the light will converges or diverges in the focus that is located halfway between the center and the surface, but due to their shape similar to a sphere which has infinite surfaces the reflected light will scatter. Therefore the likelihood of glare effect is reduce, besides if there is glare this will shift around the shape during the day, doing the glare periods short. Different case are the planar surfaces which reflect always in one direction the light and it is maintained for long periods of time, enough to generate adverse effects on the viewers.
Now that we have considered the different factors that produce glare, here we have a list of mitigation measures. If the intention of the architect is to keep a full façade style, there are different types of cladding for glass which have as an irregular surface that produce low specular reflection. Another option is to sand the glass turn it into a rough surface. If there is a way to add an external shading such a motorized blinds or louvers, where the glare is the highest, then the effect will reduce substantially. In some cases placing trees with a considering high may work as well, like in winter when the sun is more horizontal and the angle is lower.