PERCEPTION OF HUMAN SKIN IN STREET LIGHTING UNDER FIVE TYPES OF LED SPECTRA

摘要

A panel of observers has been invited to rate and compare the quality of 5 spectra of LED sources used for street lighting, on 30 subjects. Vertical illuminance on faces was 14 lx (+/- 3 lx). All 30 subjects did not have the same type of skin. 60% were from the European Caucasian type (clear skin), 23 % from the Asian one, 17% were from the Sub-Saharan type (dark skin). All subjects were also acting as observers. Correlated Colour temperature of sources was 2200K, 2700K, 3200K, 4000K, 4800K. This was obtained by mixing cool-white, warm-white and red LEDs (for the 2200 K and 2700 K sources only). The extreme stimuli (2200K and 4800K) were rejected by all participants. When presented in pairs (Thurstone protocole), 75% of observers preferred the 3200K stimulus, 61% the 4000 K stimulus, 59% preferred the 2700K stimulus. People with Asian skin was found to be preferred under CCT of 3200 K and below, for Sub-saharan skin type it was 3200K and above, and for Caucasian around 3200 K.