As presently practiced and applied, photometry does not reflect the response of the human visual system at many light levels commonly used for nighttime lighting. Vision and photometry have never been synonymous, but this disconnect could obscure prudent light source specification for outdoor illumination. The unified system of photometry, which links photopic and scotopic luminous efficiency at nighttime light levels, provides a framework for communicating information about light sources considered for exterior lighting. Despite methodological differences, work from a recent research consortium closely matches the system of unified photometry and exactly matches its framework. This correspondence should encourage decision-making bodies as they move toward a consensus basis for specifying and communicating luminous quantities.
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