Improving our attention, reaction times and even our mood, the wavelengths of blue light are good for us — that is during the day. Blue light therapy has been used, in the morning, to improve symptoms of depression, seasonal affective disorder (SAD), jet lag, sleep disorders and even dementia. These same wavelengths may be disruptive at night however, disturbing circadian rhythm and possibly contributing to higher chances of cancer, diabetes, heart disease and obesity, though more research is needed.
What Is Blue Light?
Blue light is a color visible to the human eye with a shorter wavelength, approximately 450-495 nanometers, that produces a higher amount of energy on the visible color spectrum. The main diurnal source of blue light is the sun; however, blue light is also emitted from fluorescent lights, LEDs and electronic devices such as televisions, computers, phones and tablets.
How Does Blue Light Impact Our Sleep?
Our brain produces different hormones during our 24-hour circadian cycle to keep us awake and alert during the day and keep us asleep at night, and light plays an important role in regulating the release of these hormones. Exposure to blue light tells the brain to decrease our melatonin production, which in turn signals for an increase in serotonin production, heightening our energy. For this reason, exposure to blue light at night may cause disruption to our circadian rhythm, originally calibrated to sunlight exposure before the advent of electricity.
A 2021 study in Sleep Medicine on the effects of blue light exposure before bedtime on sleep quality exposed 11 healthy young men to three different conditions: pre-bedtime exposure to incandescent light, blue light and blue light with blue light-blocking glasses. Researchers then measured their sleep quality the next morning using the Oguri–Shirakawa–Azumi Sleep Inventory. Results suggested that blue light decreased the participants’ ratio of deep sleep per night.
There is no definitive proof that blue light exposure contributes to cardiovascular disease, obesity or cancer. However, a Harvard study studied the sleep of 10 participants and gradually shifted their circadian rhythms, wherein the participants blood sugar levels increased and their leptin (a weight-maintaining hormone) levels decreased. Further research is needed in this area, but if light exposure alters one’s circadian rhythm, the circadian shift may impact an individual’s hormone production, which can impact sleep, the cardiovascular system and metabolism amongst other bodily regulations.
A group of Harvard researchers also compared the effects of blue light and green light on melatonin production and found that exposure to blue light delayed melatonin production by twice as long as green light exposure (three hours versus one and a half hours). A study at the University of Toronto found that blue light-blocking goggles could attenuate melatonin hormone suppression.
Navigating Blue Light in the Modern Era
The research at the University of Toronto suggested that individuals exposed to blue light at night, such as night shift workers, could possibly protect themselves by using glasses that block blue light. While it may be difficult to completely avoid blue light at night in the modern era, below are a few guidelines for managing exposure to blue light:
Get Your Dose of Daytime Blue Light
- Expose yourself to blue light earlier on in the day — ideally in the morning — by going out for a walk, exercising outside or spending time in the sun.
- Use a SAD lamp during the winter to improve mood when sunlight is not readily available.
Avoid Blue Light at Night
- Avoid overuse of electronics before bedtime.
- Turn display settings on computer, phone and tablet screens to nighttime mode and dim screens.
- Use blue light-blocking glasses at night when blue light cannot be avoided.