The development of high-intensity discharge (FM) sources for automotive headlighting has raised questions about the rendering of colours by those sources, relative to the rendering of colours by tungsten-halogen sources. The rendering of sign colours has been of concern because colour is used as an indicator of sign functions. The rendering of the red of stop signs has been particularly of concern because consistent recognition of stop signs is critical for safety. This study was designed to compare the magnitudes of the shifts in chromaticity of stop signs illuminated by HD and tungsten-halogen headlamps to the range of chromaticities of stop signs under tungsten-halogen. A stratified sample of 25 stop signs was selected in Ann Arbor, Michigan. Stratification was by material (enclosed, encapsulated, microprism), age (more than five years in service, less than one year in service), and compass direction faced by the legend side of the sign (north, south). The chromaticities of these signs were measured in the field under both tungsten-halogen and HD (D 1) illumination. The shifts between the chromaticities of the signs when they were illuminated with the tungsten-halogen source and when they were illuminated with the HD light source were moderate relative to the range of chromaticities under tungsten-halogen. It is argued that, although the sizes of the shifts should not be interpreted as indicating a problem with colour rendering by HD headlamps, they are not small enough to allow the possibility of a problem to be dismissed. (A)
Abstract