In today's world, sleep experts often say that for a better night's rest, Americans shouldturn off their smartphones or iPads before sleeping. Such electronic products make the brain 21 ______  , and then influence their sleep. But according to a latest survey, more than 90% ofAmericans 22 ______  use a computer, a mobile phone or some other kinds of electronic products inthe hour before bedtime.

Researchers found that man-made light from some electronic products at night may reducethe brain chemicals that can 23 ______  sleep. The research showed that 24 ______  in the light fromcomputer screens clearly lowered the level of the chemicals which manages our body clocks andplays a(n) 25 ______  in the sleep cycle. In the study, the researchers let volunteers read,playgames and watch movies on a tablet computer in different time periods while measuring howmuch light their eyes 26 ______  . They found that two hours of sitting before a bright tablet screenat night 27 ______  the sleep chemical level by about 22%.

Then the researchers studied the college students who often used computers at night. Theygot the similar results. And researchers say that may not only cause 28 ______  , but also raise therisk of obesity(肥胖),diabetes(糖尿病)and other 29 ______ .

To be on the safe side, the researchers suggest that we use computers 30 ______  than before orturn down the screen brightness as much as possible before sleeping.