This system allowed an exquisitely precise circadian rhythm of luminescence to be measured from cell populations and even from single cyanobacterial cells.
The most prominent way to measure whether a body is entrained in this circadian cycle is by measuring melatonin secretion, cortisol, and core body temperature.
This has prompted researchers to speculate involvement, or dysfunction of the brain's hypothalamus, which controls the body's biological clock and circadian rhythm.