For thousands of years, humans have lived a 24-hour day marked by the rising and setting of the sun. We have evolved to respond to the blue parts of sunlight, regulating our waking and sleeping cycle. Most artificial light reduces our ability to see the starry night sky, but it also impacts our sleep-wake cycles, or circadian rhythms. These circadian rhythms are universal across bird, reptile, and mammal species
Unfortunately, in our modern day-to-day life, light pollution extends our “daytime” experience well past sunset, thanks to artificial lighting containing some fraction of blue light.
Sleep is Essential
Everyone is a big fan of a good night’s sleep, but as you can see, sleep is an essential part of your wellbeing and health.
Melatonin is a key chemical related to your circadian rhythm and is strongly linked to getting you ready for sleep.
In animals, melatonin plays an important role in the regulation of sleep–wake cycles. Human infants’ melatonin levels become regular in about the third month after birth, with the highest levels measured between midnight and 8:00 am. Human melatonin production decreases as a person ages. Also, as children become teenagers, the nightly schedule of melatonin release is delayed, leading to later sleeping and waking times.
Blue light prevents your body from making melatonin which can cause insomnia or prevent you falling asleep at the right time.
Light Pollution and Sleep – The Science Bit.
Think of a rainbow; can you remember all the different colours there are? We are interested in how the blue part of a light spectrum (or rainbow) affects our sleep. It turns out that the eye contains a part that is specifically for synchronising your circadian rhythm. These “ipRGC” cells react to blue light, and when they activate they send a signal to the brain that stops it producing melatonin. So if you want a good nights sleep, and if we want the animals in our habitats to sleep well, we MUST tackle the “blue light” part of our lighting at night.
For you, the best thing you can do is use a blue light filter, or “comfort filter” on your mobile phone. You can check the colour temperatures of your light bulbs and make sure they are less than 3,000K, the lower the better. (Smart lights are great, e.g. Hue, because you can set them to any colour temperature you like, for example if you have Hue lights and a google hub you can say “Ok Google, set my lights to two thousand kelvin” – try it and see!) Research on melatonin suppression due to blue wavelengths of light is available if you click here.
Red Light and Sleep
There is some evidence suggesting that red, or redder lights at twilight and night can help you fall asleep, (although other evidence suggests its the absence of blue light that acts as a passive influence.) In either case, your brain releases more melatonin as darkness falls and tends to release less when you’re exposed to blue light. The bottom line is that we need to sleep in complete darkness, and to avoid as much exposure to light of all colours in the hour or so before we want to nod off.
In a 2012 study on 20 female athletes, participants were randomly given 30 minutes of red light therapy every night for two weeks. When compared to the placebo group with no light therapy, the athletes had improved quality of sleep, melatonin levels, and performance. In 2019 a 3-week study of 19 people in an office environment showed that using a combination of red with the office white light in the afternoon improved afternoon alertness and circadian rhythms. There is growing evidence that red light plays a role in triggering melatonin production at night (maybe because we evolved over the centuries watching beautiful orange/red sunsets?)
Red Light and Sleep Inertia
Sleep inertia is a sleepy feeling that you feel after you wake up. It can affect your short-term memory and alertness. A small 2019 study on sleep inertia showed that saturated red light delivered through closed eyelids, at levels that don’t suppress melatonin, may help ease sleep inertia when we wake up.