Many people have experienced a night of sleeplessness, or waking up in the middle of the night, unable to return to sleep.

Though sleeplessness is often seen as a sign of stress or too much caffeine, the effects of artificial light also play a role.

“In order for humans to function, light photons must hit the retina. However, when there is too much artificial light at night, there may be an overexposure of photons to the retina, disrupting circadian rhythm,” said Dr. Li Li, a professor of cognitive psychology at the University of Hong Kong.

The sleeping aspect of the circadian cycle is largely controlled by melatonin, a hormone produced in the pineal gland of the brain.

Naturally, the body’s internal clock controls the time you wake up and the time you sleep by raising or lowering  levels of melatonin.

“Melatonin levels usually rise in the mid to late evening, remain high for most of the night, and then drop in the early morning hours,” Dr. Li said.

However, this normal process is affected by light. The more light there is, the less melatonin your body produces.

Eventually, if there is too much exposure to light at night, the body may not be able to produce enough melatonin to sleep.

And, in fact, this deficiency is not only affected on a day-to-day basis. The body may permanently be unable to produce enough melatonin, leading to insomnia.

The consequences of melatonin depletion are potentially far-reaching.

According to Professor Samuel Ho of the University of Hong Kong, melatonin is also a hormone that slows the risk of cancer.

“Melatonin impacts the endocrine system and prevents cancerous growth formation and development,” Ho said.

In women, decreased melatonin could put them at an increased risk of breast cancer and large intestine or rectal cancers.

Beyond increased risk for cancer, an irregular circadian rhythm may also lead to weight gain, impulsive behavior and

slower cognitive functions.

Both specialists recommend using thick curtains and blackout shades, with no artificial light present in the bedroom at night.

“One of the tricks I recommend is to shut off your bright light 30 minutes before sleep, so you can signal to your body that it is nighttime. Don’t bring any electronics or anything with a light emitting from it, and don’t stare at the computer or anything with a screen,” Dr. Li said.

Although light is such an important part of our lives, artificial glow late at night does result in dangerous and frustrating consequences.