PITY the poor pineal gland, tucked behind the thalamus in a gap between the brain’s hemispheres. It has a simple task—to make melatonin, a hormone that regulates sleep. In days gone by, it would start doing so after sunset, ramp up to a maximum in the middle of the night, and then taper off toward the morning. The result was regular, dependable periods of sleep and wakefulness.
Modern life, though, is confusing for the pineal because its signal to start work is the absence of light—specifically, of blue light. This part of the spectrum radiates by the bucketful from light-emitting diodes in the screens of phones, tablets and laptop computers. As far as the gland is concerned, that turns night into day. Study after study has suggested night-time use of screen-based gadgets has a bad effect on peoples’ sleep. Indeed, things are getting worse as screens get smaller and are thus held closer to the eyes. As a consequence there is a tidy market in devices and apps which regulate the amount of blue light a screen emits.