You have probably heard about how eyes need optimum lighting to function properly. The truth is, our eyes are well-adapted to function in a variety of conditions, including in both low light and high. There are a couple of situations, however, in which the type or level of light is important.
Reading in the Dark
The most commonly held idea about the effect of light on eye health is that reading in the dark is bad for your eyes. This is mostly a myth. Reading in low light has never been shown to have a long-term effect, positive or negative, on eye health.
Low light does, however, create eye strain—a short-term condition that can cause discomfort. The iris relaxes to open the pupil as wide as possible, but at the same time the muscles that control focus must contract to make the text clear. The sustained effort of these muscles working hard eventually results in muscle strain. Eye strain can result in sore eyes, blurred vision, and headaches. So while reading in the dark will not damage your eyes long-term, optimum lighting is always better for your eyes.
Light and Sleep Patterns
Another, lesser known concern regarding the effect of light on health is the effect of light on sleep patterns. Humans evolved sleep-wake patterns to live in a sunlit world. Bright light, specifically blue wavelengths contained in sunlight, suppresses the production of the hormone melatonin through light-sensitive cells in the eye. Melatonin signals to the body that it is time to sleep and reduces alertness.
Artificial Lights and F.lux
For most of human history, this system worked perfectly: During the day, melatonin production was reduced by exposure to sunlight, while in the evening, fading light allowed melatonin to make people gradually become sleepy. People slept on regular schedules. With the advent of artificial lighting, this has become more complicated. As indoor lighting is often a warmer colour than sunlight, lacking in blue light, lights can usually be used in the evening without too great of an effect on sleep. Computer, tablet, and other electronic device screens, however, are a bright white that includes blue light, and can therefore make it harder to go to sleep shortly after use. The program f.lux helps reduce this effect by changing the colour of your computer screen almost imperceptibly based on the time of day.
In most cases, the human eye can adapt to handle a variety of light conditions. Just remember, reading in the dark is not bad for you, but if you find it uncomfortable then reading under optimum lighting might help. Finally, if you have trouble getting to sleep quickly, try avoiding electronic screens late in the evening, or use the program f.lux.