Fig. 9: The homeostatic-circadian-light (HCL) model.

Adapted from ref. ²¹. In the HCL model, light, gated by sleep, is fed into a model which captures the phase and dose response of light on the circadian pacemaker⁴⁸. The circadian pacemaker then results in a wake propensity rhythm which, when combined with sleep homeostasis, results in patterns of sleep and wake.