Figure 1. Schematic representation of the culture protocol and phase shift calculation. Retinal explants are dissected one hour before light off (ZT11) and cultured at ZT12. After 24 h in a dark incubator at 37 °C, the culture medium is changed, and retinal explants are placed in the Lumicycle for recording. The projected ZT12, at which time the medium is changed and recording is started, is then considered to be CT12 and used as a time reference. The time of occurrence of the trough and peak of the first complete PER2::Luc oscillation are determined by using this CT12 reference and by correcting the time for the endogenous period. After 4 days of baseline, the stimulation time (CT16) is determined using the peak of the third oscillation (green asterisk). The phase shift is calculated as the difference between the observed phase (blue asterisk) after the stimulation and the predicted phase (black asterisk) without stimulation of the same retinal explant.