Electric lighting 'prevents proper night's sleep' Exposure to artificial light during the hours of darkness activates arousal-promoting brain cells and suppresses the release of the sleep-inducing hormone melatonin, Prof Czeisler explained. Our bodies evolved to reach a peak of energy not in the morning but in midafternoon, giving us a "second wind" that keeps us going throughout the evening, he said. But disrupting the body clock with artificial light tells the brain it is still "daytime," meaning the second wind is pushed back by several hours. "As a result, many people are still checking email, doing homework or watching TV at midnight, with hardly a clue that it is the middle of the solar night," he wrote. Technology has effectively decoupled us from the natural 24-hour day to which our bodies evolved, driving us to go to bed later. He added that energy-efficient light bulbs and LED light used in computer and television screens is making the problem worse because it is rich in blue light, to which our eyes are most sensitive. Adjusting these devices to include more red and orange light could help reduce the effect. "Night-time exposure to LEDs is typically more disruptive to circadian rhythms, melatonin secretion and sleep than incandescent lighting," he wrote. The adverse effects of night-time light on sleep and circadian rhythms can be reduced by replacing blue-enriched light with red- or orange- enriched white light after sunset.