What is the name for light exposure that resets the organism’s master clock, as mentioned in the context of jet lag?

zeitgeber

In the study of biological rhythms, external environmental cues that synchronize the internal clock to the 24-hour solar day are given a specific term derived from German. Light exposure, which is noted as the primary environmental input capable of resetting the master clock located in the brain, is referred to as the *zeitgeber* (time-giver). While the brain's master clock uses light to set the overall daily schedule, the application of chronotherapy requires a more nuanced approach, recognizing that the timing of drug efficacy depends on the specific phase of the molecular clock operating within the target organ, such as the liver, which might be more sensitive to cues like meal timing rather than light exposure alone.