It might be fun to use your smartphone，but be careful. Too much screen time may be harmful to your health.
First，it is had for your eyes. A researcher called Sarah Hinkley says the problem comes from the blue light that the screen gives out. Looking at a smartphone for a long time can cause eye strain （视疲劳）， headaches and dry eyes. So it is a good idea to take a break every 15 minutes when you are working at a computer or using a smartphone.
Second，screen use can do harm to children's brains. A new study shows that using screens too much can affect how children's brains grow. If children use screens for more than one hour a day，they might have lower levels of white matter in their brains. White matter is a key to the development of language and reading skills. So it is wise to cut down the time of children using all kinds of screens.
Third，using screens too much will affect your sleep. According to a study，about 95% of the people between the ages of 13 and 64 use electronics （电子产品） before bed，especially the young people under 20. Doctors say that the light from those electronics at night may make you excited before you go to bed. Then it's hard for you to get enough sleep. So you'd better turn off smartphones，TVs，and all other screens an hour before your bedtime.
To keep healthy，doctors and researchers strongly advise that you shouldn't use screens for long hours.
