Several views of metal halide and high-pressure sodium lighting for outdoor applications

Metal halide (MH) lighting systems are gaining in acceptance relative to high-pressure sodium (HPS) lighting systems for many night time applications. The present paper describes a series of studies carried out to address some of the 'quality' issues associated with MH and HPS lighting systems. HPS and MH installations were compared in terms of perceptions of brightness and safety, acceptability for social interaction, facial recognition and eyewitness identification. At equal photopic light levels, a street scene illuminated at night by an MH lighting system was reliably seen as brighter and safer than the same scene illuminated by an HPS system. In terms of acceptability for social interaction, facial recognition and many aspects of eyewitness identification, the measured differences between lighting systems were not as clear.