The effects of illuminance and correlated colour temperature on daytime melatonin levels in undergraduates with sub-syndromal SAD

Abstract

Under the pressure of ensuring student visual performance, this study investigated whether improving the classroom lighting is helpful in relieving the daytime serum melatonin concentration in undergraduates who suffer from sub-syndromal seasonal affective disorder in winter. Two negative control groups (Undergraduates without sub-SAD, lighting conditions 300 lx, 4000K), two positive control groups (undergraduates with sub-seasonal affective disorder, lighting conditions 300 lx, 4000K) and six positive intervention groups (undergraduates with sub-seasonal affective disorder, lighting conditions 1000, 2000, 3000 lx and 4000K and 5000K). There were eight participants in each group (four males and four females). A total of 80 participants took part in 15 successive days of study, and the melatonin was measured every seven days. After comparing participants’ melatonin levels before and after exposure, statistical analysis revealed: (1) Participants with sub-seasonal affective disorder had a higher daytime serum melatonin level than the normal; (2) Increasing the illuminant colour temperature or illuminance in daytime can effectively restrain sub-seasonal affective disorder participants’ daytime serum melatonin secretion; (3) Compared to the 4000K intervention, the 5000K light source affected the participants’ daytime serum melatonin suppression more significantly. These results provide suggestions for classroom lighting in sunless areas from the aspect of melatonin rhythm.