When daylight enters a building, it has the power to brighten and warm rooms, shape spaces, create contrast, and highlight features. However, if this daylight is not carefully controlled and distributed, it can become a source of discomfort and discord.
When embarking on any architectural project, a number of factors and strategies need to be considered in order to exploit the benefits of daylight whilst mitigating against the potential “downside to daylight” – from orientation to glare to the colour of the interior.
The ever-changing nature of daylight means that daylight exposure is different from moment to moment, season to season and place to place. Geographical location, orientation and the surrounding environment all play a role in how much daylight is available throughout the year.
Generally speaking, equatorial regions receive the most sunshine while the poles receive the least. Buildings with windows and aspects angled to receive direct sunlight will also receive more daylight exposure. And the position of obstacles and barriers such as trees, walls, other buildings and even mountains will also affect the amount of daylight in a building.
For example, the relatively flat desert region around Yuma, Arizona receives on average 4 015 hours of sunshine each year and temperatures exceed 40°C for a third of the year. In contrast, Rjukan, situated in a mountainous valley in Norway, doesn’t receive any sunshine for 6 months of the year and temperatures barely ever reach 20°C.
While many external factors can dictate how much daylight is available to a building, what is more important is how it enters a building and how it is utilised thereafter. The placement, pitch, depth and area of glazing all have a part to play in daylight penetration. Together, these features will help ensure the right balance of light and dark inside a building.
How window features affect daylight entering a building
- In the northern hemisphere, the sun rises and sets to the south, meaning buildings with windows facing south will receive the greatest amount of direct daylight.
- The more a window is pitched towards the sky, the more daylight will be allowed in, which is why roof windows and rooflights allow in 3x more daylight than façade windows and 2x more daylight than dormer windows.
- The deeper a window is set into a building’s façade, the more acute the angle required for daylight to penetrate.
- The size, shape and number of windows obviously have an impact on daylight penetration, but it is important to note that their effectiveness relies heavily on being at the right angle and facing an appropriate direction to take full advantage of the daylight available. For example, a floor-to-ceiling window may be less effective than a much smaller window placed on the sunnier side of a building.
- While glazing affects the soundproofing and insulation of a building, the thickness and tinting of the glazing can also affect the amount of daylight passing through it.
World-renowned architect, Le Corbusier, understood the power of daylight and the impact it could have on an interior – as demonstrated in many of his designs. His mastery of controlling how daylight enters a spaces is exemplified in his design of L’Eglise Saint-Pierre at Firminy Vert.
The human eye is an amazing thing. It has the ability to adapt to light levels ranging from less than 0.1 lux (the equivalent of a distant star in the night sky) to more than 100 000 lux (the equivalent of a bright sunny day). However, it can only process a small portion of this range at a time, and it needs time to adapt – for example, when your eyes adjust to the darkness in a cinema.
In certain situations, this adaption time can also result in glare. According to the Illuminating Engineering Society (IES), glare occurs when the range of different levels of light is too extreme or a source of light is at least 1 000 times brighter than its surroundings. Good lighting design can help soften or shield the light sources from view, to ensure well-rounded visual comfort.
There are also a variety of shading systems available to limit glare and overheating before and after daylight enters a room.
External systems such as awnings or overhangs offer protection from high level sun, while vertical shading is more suited to offer protection from low level sun. The downside to most of these external systems is that they are often fixed in position and do not move as the sun moves, meaning they offer limited protection at certain times of day or year. Movable external blinds and shutters provide the most protection, however they can potentially restrict views of the outdoors.
Internal systems such as shutters and curtains can provide some protection from glare, however, heat is often still absorbed by the window. Adequate ventilation is important in order to offset any potential overheating. There are several automated systems available that can help control temperature and glare by automatically opening or closing the windows and blinds – these systems can be used in parallel with rain sensors too.
When settling on a daylighting strategy, it is essential to take into account every variable to ensure visual comfort is maintained day after day, season through season. Each element of the system – from shading and tree coverage to window layout – needs to work together to ensure light levels, glare, contrast and distribution are effectively controlled throughout the building, whether it is a bright summer’s day or a cloudy winter’s morning.
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