Metal Matters

Bright Ideas
Considerations for Effective Daylighting Design
by Rich Walker

Good daylighting design saves energy in many ways. The obvious one is lighting energy, which can represent a major portion of the total energy consumed by many buildings. Electric lights emit more heat than the same amount of natural daylight, so during the warmer months the air conditioning system has to work harder and needs to be sized for the added load.

Some products used mainly for providing natural light can also significantly reduce the amount of heat lost when substituted for more traditional products. Proper daylighting design can cut lighting energy use by up to 80 percent in some buildings, according to the U.S. Department of Energy’s Federal Energy Management Program.

Positive Effects
Beyond energy savings, studies have shown that daylight positively affects physiological and psychological well-being, from patients recovering in a hospital to students producing higher test scores in well-lit classrooms. Compared to fluorescent lighting, ample daylighting has also been found to increase retail sales and overall job productivity for workers and manufacturers.

Generally, all fenestration products can be sources of quality daylight and passive solar energy; however, additional factors need to be considered when comparisons and/or choices between side-lighting (doors, windows, and curtainwalls) and top-lighting (skylights) products are being made. The basis for the difference is quite simple; side-lighting products face the horizon and top-lighting products face the sky.

“Windows and curtainwalls also allow daylight into a space, but it is important to bear in mind factors such as the climate, latitude and orientation of a window, which can drastically affect the amount of light transmission.”

Side-lighting provides daylight and solar energy along the perimeter of a building and integrates into the daylight design of a multi-story building easily. Top-lighting can provide daylight and solar energy throughout the interior of a low rise building, on the top floor of a building or in an atrium. However, through proper building design and/or use of integral light wells or tubular daylighting devices, top-lighting opportunities still exist for lower floors in multi-story buildings.

Skylights are used widely in daylighting design in residential and commercial buildings mainly because they are the most effective source of daylight on a unit area basis. These top-lights transmit abundant light and provide a connection to the outdoor environment while allowing fresh air to circulate in the space below. Windows and curtainwalls also allow daylight into a space, but it is important to bear in mind factors such as the climate, latitude and orientation of a window, which can drastically affect the amount of light transmission.

When conditions permit, both options should be used as top-lighting is able to bring light into centralized areas of a building; daylight is available throughout the day from both ambient lighting from the sky and direct exposure to the sun; and modern transparent and/or translucent glazing can be utilized to avoid glare, aid in capturing sunlight at low angles and diffuse light to wider areas of floor space.

Following Direction
Orientation (north, east, south and west) with respect to the sun’s path is a critical factor to optimize exposure. Top-lighting offers the added advantage of obtaining the most exposure for longer periods of the day. Building features including ceiling height, surface colors and textures, light shelves, room dividers and partitions all impact the usefulness of the daylight available to the space, and should thus be considered in daylighting design.

Additionally, appropriately designed HVAC systems are critical in any energy conservation effort and automated lighting controls are essential components in multi-user non-residential environments such as offices and retail spaces to ensure lighting energy is not used when daylighting is sufficient.

The Skylight/Sloped Glazing Council of the American Architectural Manufacturers Association has developed a Daylighting Fact Sheet as an energy-saving resource to guide architects and consumers through effective daylighting designs.

The overarching goal of any daylight design is to preserve the most natural light to allow for artificial lights to only be used when necessary. While we cannot control Mother Nature, we must understand that the design of fenestration in a building, from size to location and type of glazing and accessories used, all help ensure the energy benefits of daylighting balance the costs.

Rich Walker is the president and chief executive officer of the American Architectural Manufacturers Association in Schaumburg, Ill.

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