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Effects of the spectra of innovative sources in signal lamps

Various new light sources, such as light emitting diodes (LEDs) and neon, have recently been adopted for signal lamps, or are being considered for such use. These sources expand the range of spectral power distributions (SPDs) that are of concern for automotive applications. This report reviews the interactions of such SPDs with visual conditions that are of special importance in driving and that might have spectrally selective effects. Such conditions include spectrally selective windshields, weather conditions (fog and rain), and certain visual conditions of drivers (color blindness, yellowing of the lens of the eye with aging, and wearing of sunglasses). Most of the effects of SPD can be expected to be minor. Generally speaking, even though the chromaticity constraints that are applied to signal lamps allow a range of SPDs, the chromaticity constraints are sufficient to ensure that visual performance will be predictable. A few exceptions are noted.