First, let’s understand the visible light spectrum. All electromagnetic radiation is light. The small portion of this radiation that is visible to the human eye is called the visible light spectrum. The human eye is able to detect wavelengths from 380 (violet) to 700 (red) nanometres. This spectrum, and it’s colours, are experienced every time we see a rainbow. You may remember rote learning the colours in the rainbow at school using the acronym ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet). Light enters the eye through our pupils and strikes the inside surface of our eye known as the retina. The retina has light sensing cells called rods and cones. The rods detect light intensity (i.e. lux) and the cones detect different wavelengths and therefore, colour. Once the light hits the retina, it sends an electrical impulse to the brain. Blue light, which has a wavelength of 420-480 nanometres, once detected by the brain can suppress melatonin. Why does this matter? Because melatonin directly affects our circadian rhythm.
Our circadian rhythm dictates our cycle of sleeping and waking. In the morning, cortisol rises and melatonin is low or ‘suppressed’. This helps us stay alert. Over the day, as the body prepares itself for sleep, cortisol drops and melatonin rises. This is what is supposed to happen. Blue light, even in short durations, suppresses melatonin. This is useful in the morning and horrible at night.
So what are the common sources of blue light? Conveniently, the sun is the biggest source of blue light which further drives the case for morning sunlight exposure. Other common sources of blue light include fluorescent/LED lights and of course, digital screens such as smart phones, laptops, desktops, tablets and TVs. Many of these, in particular digital screens used at night, are common culprits that explain poor sleep duration and quality.
Blue-blocking glasses, also known as amber glasses, are plastic glasses that primarily block blue light. There are many studies which show promising results that wearing these glasses at night reduces blue light exposure at night thereby increasing sleep duration, sleep quality and sleepiness prior to sleep with fewer awakenings. However, as you can see in the table below, they haven’t really been tested on that many people. There are also some studies with conflicting findings. I have decided to experiment on myself with blue-blocking glasses. I will share my findings.
Hester, Landon, Dang, Deanna, Barker, Christopher J, Heath, Michael, Mesiya, Sidra, Tienabeso, Tekenari, & Watson, Kevin. (2021). Evening wear of blue-blocking glasses for sleep and mood disorders: a systematic review. Chronobiology International, 38(10), 1375–1383. https://doi.org/10.1080/07420528.2021.1930029
Lifestyle prescription: Turn off all digital screens 90 minutes before sleep. Useful hacks: Buy an old school retro alarm clock so you can avoid setting an alarm on your smartphone.
If you know someone who will find this useful, please share this newsletter with them. There are more articles on sleep to come.