The association between correlated colour temperature and scotopic/photopic ratio

The S/P ratio is a design parameter that may be considered in road lighting. This article compares the S/P ratios and CCTs of the 297 light source spectra identified in IES TM-30-15 to test the assumption that higher S/P ratios demand higher CCTs. The results suggest that, for a given lamp type, there is a strong association between S/P ratio and CCT, and hence that for a given CCT only a small variation in S/P ratio is available. However, the results also suggest that a larger variation in S/P ratio is possible if the lighting designer is able to consider a change in lamp type.