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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:

  1. develop a skylight photometric test protocol,
  2. build a skylight goniometric test chamber
  3. test 22 skylight/light well combinations under clear skies for each 10 degree increment of solar elevation
  4. test the same 22 skylight/light well combinations under overcast skies
  5. publish public domain photometric test reports for each test
  6. 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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Copyright: Heschong Mahone Group, Inc. 2012