Wikipedia says the opposite about low-pressure sodium lamps:
Quote:
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LPS lamps are the most efficient electrically-powered light source when measured for photopic lighting conditions—up to 200 lm/W, primarily because the output is light at a wavelength near the peak sensitivity of the human eye. As a result they are widely used for outdoor lighting such as street lights and security lighting where faithful color rendition is considered unimportant.
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High pressure sodium has additional phosphors and Sodium electron excitations and is a whole different ball game.