Light has a powerful influence on the circadian rhythms of humans. But before I delve deeper into its impact on humans…

What Are Circadian Rhythms?

Have you ever realised that you are inclined to feel energized and sleepy around the same period every day? Well, it is due to the work of your circadian rhythm! It is a 24-hour internal clock functioning subconsciously and shifts between drowsiness and alertness at regular intervals.

 

 

When it is dark at night, our eyes send a signal to the suprachiasmatic nucleus (SCN) in the hypothalamus that it is time to go to sleep. The pineal gland in the brain then releases melatonin, a hormone which provides various health benefits. According to the International Dark-Sky Association, “it has antioxidant properties, induces sleep, strengthens our immune system, reduces cholesterol and helps in the functioning of the thyroid, pancreas, ovaries, testes and adrenal glands.” Exposure to artificial light at night can hence disrupt our circadian rhythms by stimulating the SCN and suppressing the production of melatonin.

 

However, just how much light is considered too much?

Recent studies have shown that our circadian rhythms can be disrupted by light intensities as low as around 180 lux. This implies that light sources used to illuminate our own homes and workplaces are more than sufficient in altering our biological clock and circadian rhythms!

In experimental studies involving rodents, repeated exposure to dim light (50 to 300 lux) at night led to irritability, anxiety and depressive-like behaviours, higher propensity to obesity, poorer learning and memory abilities.

Likewise, correlational studies on humans have found that long-term exposure to light at night, relate to sleep disturbances, cardiovascular disorders, gastrointestinal disorders, metabolic alterations, higher susceptibility to cancer and depression.