Shall We Turn off Devices at Night? Using tablet computer like Apple's iPad just before bed can lead to a poor night's sleep, according to some researchers, who are warning that the blueish light the screens emit (发出) can stop users getting a good night’s sleep. That is because this type of light mimics daylight, convincing the brain that it is still day time. Blue light suppresses production of a brain chemical called melatonin ( 褪黑激素 ), which helps us fall asleep. This is because our brains have evolved to be wakeful during daylight hours. By contrast, light which is more orange or red in tone does not suppress melatonin production, perhaps because our brains recognizes it as a cue that the day is ending. Neurologists have known for years that staring at screens late in the evening can disrupt sleep, no matter whether they are television screens, computer screens or mobile phone screens. However, because mobiles and tablets are by nature portable, more people are taking them into the bedroom. Users also tend to hold them much closer to their eyes than a computer or television screen. Researchers are warning that looking at tablet displays for more than two hours “ leads to a suppression of our natural melatonin levels as the devices emit optical radiation at shortwave lengths ” --- in other words, they emit blue light. They say, “ Although turning off devices at night is the ultimate solution, it is recommended that if these devices are used at night displays should be dimmed as much as possible and that the time spent on them before bed should be limited. ” they drew their conclusions after measuring melatonin levels in 13 volunteers after they had spent time viewing iPads at full brightness at a distance of 10 inches for two hours. Researchers know that persistent disruption to sleep patterns can lead to an increased risk of obesity, and even breast cancer. However, these studies tend to be comparisons between those with chronic sleep disruption, such as long ter shift workers, and those who have normal sleep patterns.