(46-50 閱讀三)People spend about a third of their lives asleep and cannot survive without it. Scientists have long understood the importance of getting enough sleep and the key part played by light exposure can sometimes be overlooked. The reason light is so important is that it sets our circadian rhythm, or body clock, via specialized light sensors within the eye.Our eye detects the light and dark cycle within our environment and adjusts the body's circadian rhythm so that the internal and external day coincide. This is so powerful that that people who have very severe eye damage can find their body clock is thrown off, leading to sleep problems. Jet lag is the most obvious example of the effect light can have. Exposure to light in the new time zone helps our body clock to local time, telling us the right time to sleep.We have become a light deprived species, and this has far reaching consequences for the quality of out sleep, and consequently our well-being. The optimum amount varies form person to person, but we do know that our bodies need exposure to very bright light that the majority of indoor lighting does not provide. One notable side effect is Seasonal Affective Disorder(SAD), a form of depression thought to affect 2-8 % of Europeans, which is linked to lack of sunlight exposure.Minimizing light exposure before you go to bed, and trying to get us much morning light as possible, are simple steps that could help most people to regulate and improve their sleep.
46.What is the article mainly about?
(A)Light is the key to a good night’s sleep.
(B)Body clock is linked to mood disorder.
(C)Sleep and wake up early can boost your health.
(D)Life is really harder for night owls.