Dr. Martin Moore-Ede

The body runs on a roughly 24-hour clock that takes its main cue from light. Bright, blue-rich light in the morning helps set this clock for the day. Darkness and dim, warm light in the evening let the body wind down for sleep. Modern life often reverses this, with dim indoor days and bright screens at night. This conversation looks at how the timing and colour of light reach the body clock, and why matching light to the natural day and night may support sleep and general health.

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.