"My mother says that it's bad for your eyes to read in the dark only by the light of a torch. Is that true, or is it just an old wives' tale?"

 

Low light strains the eyes because the eye muscles do not receive a clear signal. Dim light stimulates the eye to relax and causes the pupil to dilate. The light from the torch, however, stimulates the pupil to contract in order to get a sharp image.

The weaker the light, the lower the contrast between the letters and the paper, so that the eyes have to work harder to decipher the words on the page. Both phenomena result in the eyes tiring more quickly than in normal light conditions. They quickly become dry and start to itch, because the increased focus on the page means you blink less. This often leads to headaches and slightly blurred vision.

 

However, these are only symptoms that all disappear again after sufficient rest. The eyes are not damaged in the long term as long as they get enough relaxation.