Daylighting - The Benefit of Natural Light

By Greg Richardson

Daylighting is the controlled admission of natural light into a space through windows, skylights, and other transparent surfaces to reduce or eliminate electric lighting. A well-designed daylighting system can provide more light with less heat gain than any of the most efficient electric lighting sources. Not only does this translate into extremely efficient lighting, but several studies have shown that people respond positively to daylight: They feel better, they work better, and they learn better.

The major factors that should be taken into consideration when dealing with daylighting include both window specifications (size, spacing, orientation, glass selection, glazing, etc.) and interior design (reflectance of interior surfaces, location of interior partitions, necessary illumination levels, etc.). Additionally, a project may need to incorporate these changes into the balancing of heat gain and loss, and prepare for both glare control and variations in daylight availability.  

There are numerous ways to achieve effective daylighting in a building. Most of them are associated with the structural components and design of a building, but some may be introduced as a renovation. The most common daylighting techniques include the use of:

• Louvers
• Skylights
• Light tubes
• Clerestories
• Light shelves
• Roof monitors
• Vertical baffles
• Sawtooth roofing
• Photocontrol systems (which use sensors to turn off or dim electric lights to appropriate levels automatically during daylight hours)

Sample Techniques -

In addition to adding pathways for light to enter, building design strategies can affect the availability of natural light. For instance, allowing light to penetrate high into a space allows it to travel deeper into a room, as does sloping the ceilings away from the windows to reflect the light. Increasing the perimeter of the building will also increase the usable daylighting area, and so will changing the orientation of the building to mirror the path of the sun through the sky. Another issue to consider is that direct sunlight often causes uncomfortable levels of glare. Filtering direct sunlight with vegetation, curtains, louvers, or other means will help to distribute it evenly.

In addition to being naturally occurring and free, daylighting can extend the life of lamps and ballasts by a factor of two, since they are not used as often during the day. This means that embodied energy, mercury use, and disposal costs are all roughly halved, as well. Additionally, the unwanted heat generated by electric lighting can be minimized through daylighting and result in a reduction of cooling loads by up to half.

To learn more about daylighting and how to integrate it into your building’s design, there are several websites that are publicly accessible. The Radiance Synthetic Imaging System offers free lighting simulation software, the Whole Building Design Guide provides easy-to-follow, in-depth detail on daylighting, and the Sustainable Building Technical Manual contains a detailed section on daylighting strategies.