Using daylight in your building is a key strategy for passive design. Letting sun into your building impacts visual comfort, as well as thermal comfort. Understanding how light from the sun enters a building as well as how to use the light once it is in a building are important considerations for successful daylighting.
Like most things, daylighting has advantages and disadvantages. But by becoming skilled at understanding the technical components of daylighting, you can make sure to maximize the advantages and minimize disadvantages.
|Advantages and disadvantages of daylighting
Adapted from Leonard Bachman, University of Houston
Sunlight vs. Daylight
Because the sun is predictable, daylight can be a reliable light source.
Sunlight is considered as the light that enters a space directly from the sun. This type of light is generally not good for lighting an interior space. Direct sunlight can produce glare and excessive heat gain.
Daylight or skylight describes the desirable natural light in a space. Daylight results in a perceived even distribution of light that avoids the glare and ill effects of direct sunlight. You can use BIM software tools to help improve your daylighting strategies (see Daylighting Analysis).
Although natural light comes from the sun, you don’t want direct sun for daylighting design.
- Daylight is diffuse natural light from the sky. For daylighting design, you DO want daylight.
- Sunlight is direct light from the sun itself. For daylighting design, you DON’T want sunlight. It creates light that is too intense and can bring unwanted heat.
The availability of daylight is dictated by the conditions of the sky at a given point in time; which is mostly controlled by the density of cloud cover. The International Commission On Illumination (CIE) classifies fifteen different types of sky conditions that can be associated with noticeably different luminance distributions.
When conducting daylighting analysis it is important to design for a range of conditions. This means making sure that you analyze a range of sky conditions, not just a bright and clear sky. It’s unlikely that these conditions well be true for every hour of every day. Good analysis will consider bright and clear sky as well as an overcast sky.