Considerations for Effective Daylighting
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
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.
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
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.
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
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
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,
Architects' Guide to Glass & Metal
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