Optimum use of daylight
Daylighting is an up-to-date design discipline that promotes greater use of daylight in buildings.
The basic objective is to position transparent surfaces (such as windows, skylights or continuous glazing) and interior reflective surfaces appropriately so that natural light can provide effective illumination throughout the day.
While an essential part of daylighting undoubtedly relates to the planning of the building site and the architectural design of the building envelope, it should not be underestimated that coordination with two key functions of building automation systems such as artificial lighting and shading is also essential for its effectiveness.
Natural light as a resource
Daylight is the combination of direct and indirect light from the sun throughout the day; of all the solar energy received at the earth's surface, 40% is visible radiation.
The interiors of buildings need light to carry out various activities and the natural component is a very important resource that can have beneficial effects on people and the energy balance. Recognizing this, the EN 17037 standard was published in 2019 to promote the wider use of natural light - defined as that 'visible part of global solar radiation' - for indoor lighting.
The standard provides information on how to use this light component to provide illumination and limit glare while also defining principles for calculation and verification and considering the typical variability of natural light throughout the day and year. The standard applies to rooms regularly occupied by people for long periods, except in particular cases where natural light is incompatible with the work's nature and task.
UNI EN 17037 standard defines the fundamental contributions of daylighting as:
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The external view. Openings not only provide natural light but also allow occupants visual contact with the area surrounding the building. This is seen as a positive factor in reducing the fatigue associated with long periods in the confined environment, providing an opportunity to relax and relieve excessive concentration;
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Protection from glare. When there is direct sunlight, viewing outdoors can cause glare, a negative phenomenon caused by areas that have a much higher luminance than the eyes have adapted to in the indoor environment. To reduce this risk, shading devices should be provided;
- Exposure to sunlight. This factor is of great importance in the quality of the indoor environment and contributes to the well-being of the occupants, especially in buildings such as hospitals, homes or school buildings. The use of shading devices can reduce possible thermal and visual discomfort.
Why is daylight important?
- 63% of people consider daylight to be the most important aspect of a home (Home wise survey, "Without space + light")
- Daylight improves visual and psychological comfort and has a positive effect on people's performance, attention, satisfaction, and ability to learn
- Daylight relieves seasonal affective disorder (SAD, a form of depression)
- Exposure to sunlight has been shown to be an effective treatment for sleep disorders
- Daylight through windows is the key factor in providing the high levels of light needed to support the functioning of the circadian system.
(source: www.lrc.rpi.edu)
Limits to the use of daylight
Where permitted by the building envelope, natural light can be the primary source of daylight during the middle of the day for most of the year through openings in vertical (doors, windows, glazing) and horizontal (skylights) surfaces.
But the availability of natural light outdoors is typically very variable, depending for example on the time of day, weather conditions and time of year. Latitude also plays an important role: in the capitals of the European Union, the average annual hours of daylight available range from 3,600 in Valletta to 1,550 in Brussels and 3,150 in Rome.
Although the positive effects of daylight on human beings have been scientifically proven, it is important to ensure that it is glare-free and respects the privacy of the occupants.
Finally, in the summer season, thermal loads—generated in the interior by direct sunlight passing through the glass surfaces—must be limited to avoid wasting energy through excessive air conditioning use.
Because of these limitations, in real buildings, the level of illuminance needed for good comfort cannot be achieved by natural light alone but always comes from an intelligent combination of natural and artificial light.