Low-pressure Sodium Lighting and Visual Performance

Brief summary and comments on
A. Lewis, "Visual Performance as a Function of Spectral Power Distribution of Light Sources at Luminances Used for General Outdoor Lighting," JIES Winter 1999

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Christian B. Luginbuhl
U.S. Naval Observatory Flagstaff Station
PO Box 1149
Flagstaff AZ 86002
cluginbuhl@nofs.navy.mil

Version 1.0
26 May 2004

This paper investigates three aspects of visual performance related to lighting level and lamp type: contrast threshold, reaction time (identification of grating orientation), and reaction time ("realistic task" - identification of the direction a person is facing, presented as a slide to the experimental subjects). All study subjects were 23 years old and younger. At the lowest lighting level investigated (0.1 cd/m²), and for the "realistic task," lighting levels required to achieve performance equal to the reference lighting type (incandescent) were 10.5 (LPS), 9.0 (HPS), and 1.0 (metal halide). At 1 cd/m² the effect shrinks to 2.1 (LPS), 1.9 (HPS), and 0.7 (metal halide). These findings are extraordinary in that they show a much stronger effect than has been found by other investigators in the field (see here), particularly since the "realistic task" appears to involve principally central (foveal) vision, where spectral effects are expected to be minimal. Note that the lowest lighting level investigated (0.1 cd/m²) is lower than any commonly recommended target luminance, though it may be relevant for adjacent or "peripheral" areas such as roadsides.

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