Light affects sleep differently
Whether light in the evening disturbs sleep may depend more on the person than previously thought, according to a research team led by Andrew J. K. Phillips from Monash University in Melbourne after testing 55 young adults.
Exposing yourself to bright light for hours in the evening impedes the body's own production of the "sleep hormone" melatonin. And since this signals the beginning of the night to the inner clock, you sometimes only get tired later. Blue light in particular has long been suspected of disrupting sleep. Phillips and his team wanted to find out whether this effect occurs equally in all people. They therefore exposed their test subjects to different levels of bright light for five hours in the evening over a period of several weeks. The chronobiologists collected hourly saliva samples, with which the melatonin level could be reconstructed.
Some of the test participants reacted extremely differently to the lighting: In a very sensitive test person, six lux (which roughly corresponds to the illuminance of several candles) would have been enough to halve the melatonin level, the scientists report. For another person, on the other hand, a total of 350 lux were required (bright office lighting). On average, exposure to 25 lux in the four hours after sunset, equivalent to dim room lighting in the evening, halved melatonin production.
The researchers did not examine whether the subjects fell asleep later. However, previous studies suggest that there is a clear connection with the release of melatonin - again depending on the person.
