Joint effects of wavelength and ambient luminance on discomfort glare from monochromatic and bichromatic sources.

Abstract

Recent developments in headlighting and rearview mirror technology have increased the need to understand possible effects of the color of a glare source on discomfort glare. The present study addresses that need by partially replicating and extending a previous study in which subjects rated the discomfort glare experienced from monochromatic stimuli (Flannagan, Sivak, Ensing, & Simmons, 1989). In the present study five young subjects rated the discomfort glare experienced from monochromatic stimuli of 480 nm and 577 nm, as well as from a bichromatic mixture of those wavelengths that was balanced to appear white. Two levels of background luminance were used: 0.034 and 3.4 candelas per square meter. Results are summarized in terms of discomfort glare efficiency functions, analogous to the photopic and scotopic luminous efficiency functions. At the dimmer background luminance level glare efficiency follows scotopic luminous efficiency. At the brighter background level glare efficiency shifts partially toward photopic luminous efficiency. Discomfort glare ratings for the bichromatic mixture agree well with predictions based on an additive combination of responses to the monochromatic stimuli, although the precision of the data is such that we cannot rule out the possibility of a substantial departure from additivity. These results suggest that the glare properties of colored sources can be predicted by using an efficiency function similar to the scotopic luminous efficiency function. The possible consequences of this for glare from high intensity discharge (HID) headlamps are discussed. Calculations indicate that the glare properties of most HID headlamps should be similar to those of tungsten-halogen. Primarily because of uncertainty about the state of dark adaptation of drivers at night, these laboratory results should be supplemented with data from field conditions.