Figure 4

Nocturnal human melatonin suppression data [24, 26, 27, 30, 38, 39] (left ordinate), plotted as a function of CL quantities (abscissa) predicted by the model of Rea et al. [36]. Also shown is the best-fitting four-parameter logistic function [40] to all of the data from threshold to saturation. The circadian light quantity CL was formerly named circadian stimulus (CS) [36]; CS (right ordinate) now refers to the effective stimulus based on nocturnal melatonin suppression.