A recent study by Heschong Mahone Group of
Worker productivity—much of which can be directly correlated with daylight—can increase by 20 percent with good design or decrease by 20 percent with bad design.
The benefit of using daylight in schools is well documented. Studies show that students have improved performance on standardized testing if they have been in classrooms that primarily use natural light rather than artificial light.
Daylight does not equal sunlight. Daylight is cool in color and temperature, and by definition, daylighting actually involves keeping direct sunlight out of buildings and bringing diffuse light in.
Design is key to ensuring that the incoming daylight works with, and not against, other building systems such as HVAC (heating, ventilating and air conditioning) and electric lighting. Good daylight design will reduce the use of electricity by turning off electric lights and reducing air conditioning loads.
By incorporating appropriate daylighting design, building owners can meet 25 to 33 percent of the requirements necessary to obtain a Silver-rated LEED building. The LEED (Leadership in Energy and Environmental Design) Green Building Rating System™ is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings from the Washington, D.C.-based, U.S. Green Building Council.
Daylighting test equipment –heliodon
The heliodon helps designers examine how the direct rays of the sun interact with an architect’s building design. A tilting/rotating table serves as the earth, and a stationary 1,000-watt theatrical light source as the sun. The table can be adjusted to represent the latitude, tilted to simulate any month of the year, and rotated to analyze any time of day.
When a physical model is tested on the heliodon it is typically rotated through the sun angles present on June 21, Sept. 21 and Dec. 21. This yields the sun pattern data for the highest, average and lowest sun angles for the chosen location.
The primary tool for recording these tests is a digital video camera. When mounted to a model, it will record the movement of direct sun patterns entering the space throughout the day.
Typically these studies seek to examine shading devices that eliminate direct sun from areas where visual tasks are critical. Direct sun can cause problems of heat gain and glare. The heliodon takes the guesswork out of complex sun-angle geometry and often provides surprising results.
Overcast sky simulator
Testing for the overcast condition occurs in a mirror-box artificial sky. It conforms to the “International Overcast Sky” standard of being three times brighter at the zenith (directly overhead) than it is at the horizon.
The mirror-box overcast sky simulates a dome of light that provides diffuse light equally from all sides. Note that a patch of overcast sky is up to 10 times brighter than a section of clear blue sky.
The primary method of testing design decisions in the overcast sky is through photography. This allows designers to examine the perceptual quality of a space and the feeling of brightness (diffuse light on vertical surfaces and ceilings) and to ensure that a balanced luminous environment (from perimeter to deep interior) is created.
Photocells are used to measure the percentage of available daylight (Daylight Factor) entering a space. A “control cell” on top of the model orients toward the zenith to measure the amount of available daylight. Inside the model, photocells measure the amount of light reaching the interior.
Dividing the interior readings by the value of the exterior reading yields the Daylight Factor (percentage of outdoor illumination indoors). These numbers serve as a rough measure of the daylighting design performance and factor into LEED certification.
