Shana Hussin, RDN

Your body has an internal clock that uses light to help set sleep and other daily rhythms. Light in the evening and at night can shift that clock and lower melatonin, the hormone that helps you sleep, and the effect depends on brightness, timing, duration, and wavelength. Blue-rich light can have a particularly strong effect on the clock, but blue light alone is not the whole story, and reducing bright evening light in general is a reasonable, low-risk habit. In this episode a circadian scientist goes much further, arguing that night-time blue light is a major cause of the obesity and breast cancer epidemics. That is a far stronger claim, and the evidence does not support it. He also sells lighting products designed to reduce blue light, which is worth weighing when judging how strongly the case is made.