Daylighting

What is Daylighting?

As the name implies, daylighting is a strategy for reducing energy use by using natural daylight for illumination in occupied buildings that allows reduction of the amount of electric lighting needed.

Calculations for the amount of lumens needed in a space for different tasks are often performed to optimize the lighting required. The amount of illumination provided by natural daylighting is calculated under varying conditions including overcast conditions so that a range of illuminances are determined and used to supplement the required electrical lighting load. Location of openings becomes a key factor as well. Studies have shown that glazing located high in a wall allows daylighting to penetrate greater distances into a room. Additionally, as the height of the windowsill increases, the point of maximum illumination moves away from the window

Natural Daylighting

In using natural daylighting as a primary source of lighting in commercial buildings, the concern becomes how to get natural daylight into spaces that are furthest away from daylight sources such as windows. Skylights are used as one method to allow daylighting to illuminate interior spaces. The general rule of thumb is to space skylights one to 1.5 times the height of the room. The most illumination is obtained when a series of smaller skylights are inserted in ceilings of rooms and have been shown to be the most energy efficient pattern of adding daylighting into interior spaces. Additionally, the use of reflective light shelfs at windows can also be used to allow daylighting to be reflected further into interior spaces as well. The introduction of highly reflective tubular skylights called Solatubes or Apollo Light Pipes allow daylight to be collected and introduced into spaces in which more conventional skylights cannot be constructed.

Fact: One study by Southern California Edison in retail spaces showed a 26% improvement in sales volume in large retail stores that had skylighting versus similar stores without skylights. Other studies have shown that retail stores that have no skylights can expect approximately 40% higher sales volume merely by installing skylights in their retail facilities.

Daylighting Interior Spaces

The addition of natural daylighting into interior spaces have been shown in many studies to have tangible productivity benefits. Some of these benefits include reduction in employee absenteeism, higher retail sales, and improved student health and academic performance. The Heschong Mahone study found that students in spaces with the most daylighting in their classrooms progressed 20% faster on mathematics tests and 26% faster on their reading examinations versus those students in classrooms with the least amount of daylighting.