Lighting for subsidiary streets: investigation of lamps of different SPD. Part 2 - Brightness

British Standard BS5489-1: 2003 permits a trade-off between colour rendering and illuminance for lighting in subsidiary streets-if lamps of high colour rendering index are used, such as metal halide instead of low- and high-pressure sodium, a lower illuminance can be used. A series of tests are carried out to validate the trade-off and this paper reports on the new brightness data from these tests. The experimental results support the trade-off but it is suggested that its application may depend on the stage of chromatic adaptation at which the assessment of brightness is made. The experimental results are compared with predictions made by four models of mesopic photometry.