Several Views of Metal Halide and High-Pressure Sodium Lighting for Outdoor Applications
Currently, high-pressure sodium (HPS) lamps are the most common type of light source used in outdoor applications. There are many advantages to using HPS lamps, including low costs for purchase and installation, generation of lots of lumens, and low operating cost. Metal halide (MH) lamps are becoming more frequently used in outdoor applications in part because of their lower initial and operating costs. They are also more efficacious than HPS lamps.
Despite these differences, there have been relatively few studies which identify the "quality" of the two lamp types, including color rendering and sense of security. Researchers at the LRC addressed this question of quality.
Results showed that, overall, the MH lamps had better "quality" of light than HPS lamps. Color appearance was better with the MH lamps, and apparent scene brightness was consistently higher for MH than for HPS lamps. MH lamps also provided a greater sense of security than HPS lamps, which is likely to be associated with he perceived brightness response.
Application of these findings can be used in a variety of ways. For instance, in scenarios where brightness and safety are not important and a sense of intimacy is desired, for example, a street cafe, then the HPS lamp would be most effective. To illuminate a highway road, the MH lamps would be a better option.
Bullough, John, MS Rea, and Y Akashi. "Several views of metal halide and high pressure sodium lighting for outdoor applications." 2009. Lighting Res. Technology. 31: 297-320.