PIER Skylight
Photometry
Photometric information, a description of
the angular distribution of light from a source, is the basis of
predicting how that light source shall light a space. Photometrics
describe the directionality and the magnitude of light from a given
lighting source. Almost all electric light fixtures sold in the United
States have a photometric report. This photometric information allows
one to calculate how the light fixtures distribute light in a room. In
the past, measured photometric information was not readily available for
skylights. As a result, lighting designers do not have the same
predictive tools for designing with skylights as they do for electric
lighting.
The Heschong Mahone Group contracted with
Lighting Sciences Inc. to:
- develop a skylight photometric test
protocol,
- build a skylight goniometric test
chamber
- test 22 skylight/light well
combinations under clear skies for each 10 degree increment of solar
elevation
- test the same 22 skylight/light well
combinations under overcast skies
- publish public domain photometric test
reports for each test
- publish the photometric test data in
IESNA LM63-1995 formatted files. These files are public domain.
Photometric information on this web site
is available for only diffusing skylights on short (one foot) light
wells. Photometric information for non-diffusing skylights and for
taller light well heights is available to lighting researchers upon
request. The Heschong Mahone Group has also
published a public domain spreadsheet, SkyFit. This spreadsheet
asks for the local time and the longitude and latitude of the location
of interest and calculates adjustment factors (lamp lumens and skylight
rotation angle). A PowerPoint presentation on the skylight photometric
download page describes how this information is used with one
commercially available lighting software. The same principles apply to
other lighting software.
- To download the photometric files
and other materials related to this project, please register here.
- To learn more about the Skylight
Testing project, follow this link to the New
Buildings Institute.
The Heschong Mahone Group directed
this research as part of the Integrated Design of Commercial Building
Ceiling Systems research element of the Integrated Energy Systems -
Productivity and Buildings Science energy research program managed
by the New Building Institute. The Integrated Energy Systems -
Productivity and Buildings Science program is funded by the California
Energy Commission under Public Interest Energy Research (PIER)
contract No. 400-99-013. The PIER program is funded by California
ratepayers through California's System Benefit Charges and is
administered by the California Energy Commission (CEC).
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