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Glare in LED Outdoor Lighting

Many of the applications where SSL has experienced rapid adoption have incumbent light sources with high brightness and glare potential, such as high-intensity discharge lamps for street and parking lot lighting and halogen lamps for PAR and MR applications. The inherently high brightness and small size of LED sources create significantly higher glare potential compared to incumbent technologies, and this concern will only worsen as SSL sources achieve higher output at higher efficacy. To help address this issue, DOE contributes to several standards committees and plans to initiate new human factors research in the near future. Current committee involvement includes:

  • CIE JTC7, Discomfort Caused by Glare from Luminaires with a Non-Uniform Source Luminance, which is in the late stages of producing an improvement to the Unified Glare Rating (UGR) that takes the luminance distribution across the face or aperture of a luminaire into account.
  • CIE TC4-52, Lighting for Pedestrians, which plans to implement an empirically derived set of recommendations for lighting pedestrian environments.
  • IES Lighting for Outdoor Public Spaces, which focuses on the specific needs of pedestrians in outdoor spaces, recognizing that glare for pedestrians is significantly different from the needs of vehicle drivers.
  • IES Discomfort Glare in Outdoor Nighttime Environments (DGONE), which is trying to develop a way to calculate discomfort glare for pedestrian, sports, and other non-roadway nighttime environments, including examining whether the CIE JTC7 approach can be applied to nighttime situations.

DOE is also investigating factors that contribute to the human glare response. An apparatus is being built at Pacific Northwest National Laboratory (by a third party) that will explore perceived glare while varying the position of a light source within the visual field (specifically near the edges or beyond the visual field), the size and luminance distribution of the light source, the background luminance surrounding the light source (specifically backgrounds that simulate nighttime conditions), and the spectral power distribution of the light source.

Using HDRI for Luminance Measurement

Compared to the use of conventional spot luminance meters, high dynamic range imaging (HDRI) offers significant advantages for luminance measurements in lighting research. Consequently, the reporting of absolute luminance data based on HDRI measurements has rapidly increased in technical lighting literature, with researchers using HDRI to address topics such as daylight distribution and discomfort glare. However, questions remain about the accuracy of luminance data derived from HDRI. A literature review related to possible sources of error identifies four sources of significant error and discusses their cause, magnitude, and available correction methods. The review also offers recommendations for minimizing possible errors in HDRI luminance measurements as well as topics for future research.

Sources of Error in HDRI for Luminance Measurement: A Review of the Literature (March 2020, LEUKOS)