“Circadian rhythm” refers to the built-in clocks  that regulate many biological processes in our bodies. Our circadian rhythms vary by individual and are not exactly 24 hours (for most people it is longer than 24 hours). There are a number of external factors that help synchronize our circadian rhythms with the 24 hour cycle present in nature, the strongest influence being light exposure to the eyes.

Light effects our circadian rhythms via the timing of light exposure, the intensity of light exposure and the wavelength of light exposure. Exposure to light causes the release of the chemical cortisol in our brains which increases alertness.  Light also interferes with the production of melatonin which is a chemical that causes sleepiness. Silversun Pickups playing “Melatonin”: https://youtu.be/bEcFkotqHg8

During the day, sunlight shifts to more short wavelength blue light. This blue light triggers the release of cortisol.  As the day progresses into dusk, sunlight shifts to the more red wavelengths and these red wavelengths lead less cortisol production and interfere less with melatonin.

Our modern world of light and electronics is playing havoc with our circadian rhythms. Most energy efficient fluorescent and LED lights produce more blue wavelength light than their incandescent predecessors. Our computer, phone and tablet screens all produce mainly blue wavelength light. Thus, our shift to energy efficient lighting and use of electronics at night is bombarding our eyes with blue light which actually signals us to be alert instead of going to sleep.

Dis-regulated circadian rhythms and sleep patterns are a health threat. From Harvard Medical School paper on this topic: “Study after study has linked working the night shift and exposure to light at night to several types of cancer (breast, prostate), diabetes, heart disease, and obesity.” Additionally, dis-regulated sleep patterns lead to feeling tired and being less alert and productive during the day.

What to do? Best practices:

• Use dim red shifted lights for night lights. Red light has the least power to shift circadian rhythm and suppress melatonin.
• Avoid looking at bright screens beginning two to three hours before bed. A recent study has found that 90% of American adults use their electronic devices within an hour of their bedtime at least a few nights a week. Another study found that compared to reading a paper book, use of an e-book before bed led to an average of 10 min longer to fall asleep and reduced the production of melatonin and reduced the amount of rapid eye movement sleep.
• If you do use electronics at night, reduce the brightness and use technology that shifts the wavelength away from blue light – such as the “night shift” feature on Apple iPhones and iPad. Here’s how to activate night shift on Apple products: https://www.imore.com/night-shift
• Here’s the Commodores singing “Nightshift”: https://youtu.be/FrkEDe6Ljqs
• Expose yourself to lots of bright light during the day, which will boost your ability to sleep at night, as well as your mood and alertness during daylight.
• In the near future it will be possible to buy light bulbs with differing wavelengths or even adjustable wavelengths.  What is optimal is to have blue wave length emitting light-bulbs during the day at home or work and then red wave length lights in the evening, especially in sleeping or pre-sleeping areas.