We have night after lights out in the faint light reading experience. Mom and Dad will warn us so weak harmful to the eyes.
In fact, when walking into a dimly lit room, the eyes will be adjusted in several different ways. First, the rod and cone cells of the retina begin to produce more light-sensitive substances that can detect light and convert it into electrical signals to the brain. Secondly, the iris muscle relaxation, resulting pupil of the eye becomes very large, allowing the eyes to collect as much light. Finally, the nerve cells in the retina can be adjusted to suit the dim light environment. When reading, the eyes must be words in the image focused on the retina. To do this, the shape of the iris and pupil control muscle contraction, so that the image can continue to focus on the retina.
If you read in low light, the visual muscles will receive a lot of mixed signals: relaxation to gather more light, but at the same time, the contraction in order to maintain the focus of the image. Visual object when there is insufficient light, the focus becomes very difficult. Because the contrast with the words of the page is not obvious, it reduces the ability of the eye to distinguish visual detail. This capability is often said that vision. Eyes need to work harder to identify the words on the page, resulting in eye muscle fatigue.
When the eyes continue to work like this for a long time, it will become tired, just as other muscles. This exhaustion will bring a lot of adverse health effects, including dry itchy eye pain, headaches, back and neck pain, and blurred vision. Since Visually single object, blink frequently enough, you may feel dry eyes, uncomfortable. All of these symptoms are not really harm the eyes, and will eventually disappear. If you stop after high-intensity activities eyesight, these symptoms did not go away, you should see an ophthalmologist promptly. Likely to encounter potential eye problems, such as myopia. In fact, visual fatigue and myopia may be some similar signs some people still think that reading in dim light would be a cause permanent eye damage.
It now appears, reading under a flashlight lighting in terms of children's vision appears to be safe. However, in the light of the direct projection does not need to read widened eyes on the page, so of course easier to read under good light. And while reading, you can also avoid visual fatigue through a number of methods, such as frequent blinking, you can also spend some time overlooking an object out of the window, or once every 15-30 minutes around the room.
(The answer from finishing HowStuffWorks)
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