The enjoyment of reading in the evening hours is often clouded by fears of long-term damage to the eyes. However, this concern is unfounded, as a closer examination of the visual process in the dark shows. There are two different types of light receptors (photoreceptors) on the retina of the eye. The rods are highly sensitive to light and are responsible for night vision, and the cones are called upon for color vision.
Visual purple is converted
When light falls on the retina of the eye it is absorbed, and the visual purple (rhodopsin) is chemically transformed and is no longer available to the eye until it is regenerated. This regeneration is only possible when the eyes are closed or when no further light can fall on the retina.
Another prerequisite for the regeneration of visual purple is a sufficient supply of provitamin A (beta-carotene), which is found primarily in carrots, cabbage and spinach. A deficiency of vitamin A may even cause night blindness, corneal inflammation or dryness of the eye.
Conclusion
Reading at dusk does lead to increased visual purple breakdown, but does not result in long-term damage because visual purple regenerates. However, it is not advisable to drive a car after reading in the dark, as the amount of visual purple and thus the visual acuity may have decreased during the evening. The next morning, however, the eyes are fully functional again, as the visual purple has completely rebuilt during sleep.