I was always told as a child to turn on the light if I was reading or playing games, because doing these things in dim light would damage my eyes. I assumed this to be true, and didn’t question it at the time, but now I’m older, I’ve grown a little sceptical of this theory. So, I trawled through the research journals to see what evidence there is.
It is not surprising to find no specific research into this because it would be unethical to test the theory and risk permanently damaging test subjects eyesight just to prove/ disprove the theory. However, in ophthalmology (eye doctor) circles, it is widely accepted that reading in dim light doesn’t damage eyesight, and this is outlined in educational material published for patients1.
This is supported by the fact that reading conditions have gotten much better with the invention and development of lighting, yet cases of myopia (short sight) are increasing. Historically, all reading would have been done by candle in very poor lighting, which, if the theory is true, would have caused far more cases of myopia than there were, and the cases of myopia should be decreasing, not increasing.
Finally, there is no identified biological mechanism by which dim light can cause myopia, so there is no real scientific substance to the theory.
Dim light can cause difficulty in focusing, which can make reading text particularly difficult. This happens because the rods in the eye do most of the ‘seeing’ at low light, and the resolution of rods is quite low compared to the cones ( the colour ‘seeing’ parts of the eye). Having difficulty in focusing can give the impression that your eyes are being damaged.
In addition to this, in dim light most people will squint to try and focus better, and in doing so, reduce the rate at which they blink by as much as 50%. One of the purposes of blinking is to lubricate the eye, and by reducing the rate at which you blink, your eyes can feel dry and sore – which can again be interpreted as them getting damaged.
Finally, although dim light doesn’t damage your eyesight, reading, and other prolonged close work can damage your eyesight, particularly at a young age when the eyes are still developing, and the association between people who do a lot of reading and myopia is well documented. In fact, it has been hypothesised that intelligence was a cause of myopia, because people in professions which required a high level of intellect (such as medicine or law) often needed glasses. In reality, the cause is probably the excessive reading they have had to do to achieve their career goals.
Despite no actual clinical trials testing the effects of dim light on eyesight, it is generally accepted that dim light has no effect on eye sight. The myth seems to have come about from a combination of a difficulty to focus on text in light, dry and sore eyes as a result of squinting in an attempt to focus, and the association of reading and other close work with damaged eyes and short sight.
1. Rubin ML, Winograd LA. Taking care of your eyes: a collection of patient education handouts used by America’s leading eye doctors. Gainesville, FL: Triad Publishing, 2003
Image courtesy of Sarah C
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No, but it can make your eyes strain, and feel dry and sore, which gives the impression of damage.