12．As more students begin to use computers for a long time，more of them are feeling eyestrain（視疲勞）．Just a few hours in front of a computer screen can make a person's eyes feel tired and painful．A number of doctors have studied this growing problem and have found ways to deal with it．Following their advice will help keef computer users more comfortable．Here is some advice．
The light in a room shouldn't be brighter than the computer screen itself．In many classrooms，however，the lights are far brighter than they should be．Students can prevent some of this light by wearing baseball caps if they are allowed at school．
A special computer screen should be used to cut down on bright light because it is especially tiring to the eyes Another problem to avoid is the wrong kind of contrast（對比）．It is best to have dark letters on a light hackground．This causes less eyestrain than light letters on a dark background．
Students should he seated so that they are looking down at the computer screen rather than straight a head，which is a far more tiring angle（角度）．The top of the screen should be a little lower than the top of the head．
The length（長度） of time students spend in front of a computer screen leads greatly to eyestrain．Students should rest a while by looking away from the screen every fifteen to twenty minutes．During that time they should either close their eyes or look at something at a distance．Long-term computer use can dry out the eyes，so students shouht remember to blink（眨眼）often while in front of the screen．
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