DOE has published the results of a study of the expected contributions to sky glow from converting high-pressure sodium (HPS) street lighting to broader-spectrum (i.e., white light) sources, with specific focus on LEDs, and presents the contributions in a manner relative to HPS baseline conditions. These conditions represent typical conversions in the U.S. and include changes in spectral power distribution (SPD), percent uplight, and lumen output.
Drop-lens (left) and flat-lens (right) cobra head street light fixtures. (Image: DOE)
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All of the LED product conversions reduce sky glow relative to an HPS baseline when the results are expressed as unweighted radiant power, for both near and distant observers.
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When the results are scotopically weighted to evaluate the effects on human vision, some LED products reduce sky glow for the near observer compared to the baseline, and others increase it, depending on their relative content of shorter wavelengths. An important related finding, however, is that CCT is not a very reliable predictor of sky glow impacts, especially when scotopic weighting is not applied.
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Overall, the results for LED conversions in this study ranged from a low of 0.2 to a high of 1.6 times the baseline HPS sky glow, depending on the combination of variables and factors studied.
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For a distant observer under the scenarios modeled, even at only 40 kilometers from the city center, the elimination of uplight that occurs in typical conversions nearly removed (by 95% or more) the contribution to sky glow from the street lighting system, for both the unweighted and scotopically weighted results, for all SPDs and atmospheric conditions.
For a closer look at the findings, download the full report.
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