Fig 3.

Qualitative fits: Simulation of the three conditions shown in Figure 1: constant dark (heavy line), constant light (dashed line) and 50∶50 alternation with a 20-min cycle duration (light black line). Parameters: V  =  1, k₁D  =  .08, k₁L  =  .01, k₂  =  .8, x₁(0)  =  1. (Since the 3 curves in Figure 1 came from 3 separate experiments, slightly different parameter values would normally be needed for exact fits to each—but see discussion of Figure 7, below).