Why Do Circadian Rhythms Care About Blue And Green Light?

‘Exposure to all colour of light helps control your natural sleep and wake cycle, or circadian rhythm’ (WebMD). However, exposure to blue light and green light at the wrong times of day can interfere with your body’s ability to prepare for sleep.

Blue light for increased alertness

A cold light will emit more blue wavelengths and have a greater potential disruptive effect on our circadian rhythms if we are exposed to it at the wrong times of the day.

Blue light (wavelengths from 460 to 480nm) is very beneficial in the mid-late morning to wake us up and during the daytime to make us feel alert. It has even been linked to people making fewer mistakes and improved wellbeing. It is the overexposure to blue light that begins to cause issues.

According to research from Brigham and Women's Hospital in Boston, exposure to blue light during the day can make you feel more alert and improve reaction time, focus, and productivity. "Photoreceptors in the eye, which link to the areas of the brain that control alertness, are most sensitive to blue light. Therefore, when blue light hits them, the receptors set off activity in those brain regions, making you more energized," says Shadab A. Rahman, PhD, the study's author’ (Ketchiff N/A).

Blue light is prevalent in sunlight, so your body naturally absorbs the most during the summer and much less in the winter. Because of this, researchers suggest adding blue light to indoor atmospheres, as opposed to the standard yellow lights, which are typically used, may help boost mood and productivity year-round. Blue lighting can be added to desks so that the photo-receptors receive the right amount of blue. You could position your desk in front of a window to increase your exposure, but the best solution is to get outside and absorb some of the natural light.

Blue light can be problematic because it has a short wavelength that affects levels of melatonin more than any other wavelength does. Light from fluorescent bulbs and LED lights can produce the same effect. Normally, the pineal gland in the brain begins to release melatonin a couple of hours before bedtime, and melatonin reaches its peak in the middle of the night. When people read on a blue light-emitting device (like a tablet, rather than from a printed book) in the evening, it takes them longer to fall asleep; plus, they tend to have less REM sleep (when dreams occur) and wake up feeling sleepier— even after eight hours of shuteye (National Sleep Foundation N/A).

However, small changes can be made to avoid the amount of blue light exposure in the evening. You can adjust your laptop/computer screen brightness and colour so that the colour moves away from blue to more of a reddish/yellow tone after a certain time. Also, using warmer coloured bulbs in bathrooms and bedrooms help to minimise the impact; red light has a higher wavelength; therefore, it does not suppress the release of melatonin.

Please find out more about the specific effect of blue lights on our circadian rhythm here.

Green light for pain relief

Green is a calming colour, conveying hope, soothing and healing. The colour green is the most visible and sensitive colour to the human eye (Philips 2015).