Blue Light and Sleep: What Nurses Need to Know

Beverly M. Hittle, PhD, RN; Imelda Wong, PhD

Disclosures

Am Nurs Journal. 2022;17(3) 

In This Article

Sleep and Circadian Systems at a Glance

Natural wake and sleep times can be explained by the two-process sleep regulation model: homeostatic sleep pressure and the circadian system. Homeostatic sleep pressure refers to the need to sleep, which begins building in the body the moment we wake up, so by the end of the day we feel ready to sleep. The circadian system is controlled by the suprachiasmatic nucleus (SCN), located in the hypothalamus. The SCN, also called the master clock or "conductor" of the circadian system, paces the timing of all the body's circadian rhythms and physiologic functions such as the sleep–wake cycle. The SCN relies on external cues (such as light) and internal cues (such as the time of day meals are consumed) to keep the clock on schedule and aligned with our day–night earth cycle.

Light is one of the strongest external signals keeping the circadian system in time with the 24-hour period. Although several light properties can affect the circadian system, wavelength is the most significant. "Blue light" refers to shorter wavelengths in the light spectrum and are stronger influencers on the circadian system than red or orange light (longer wavelengths). Daylight, bright indoor lights, and light from electronic devices all contain blue light. When we're exposed blue light sources, the retina detects the short wavelengths and sends a signal to the SCN that it's daytime. As a result, the SCN turns off the circadian system's nighttime physiologic functions and turns on daytime functions. For example, circadian rhythms regulate the hunger and satiety hormones ghrelin and leptin, which circulate more widely during the day to accommodate our response to food. Likewise, in the evening, the decrease in natural sunlight signals the SCN to release melatonin, easing the body to sleep.

Because our circadian system is more sensitive to bright light at night, shift workers may experience suppressed melatonin production, making it difficult for them to sleep. Regular exposure to light at night also can shift circadian timing, resulting in a delayed sleep phase (pushing sleep timing later than our bodies would naturally fall asleep) and contributing to a misalignment of our circadian system with the day–night earth light cycle. Circadian misalignment and exposure to light at night also have been implicated in disease development, including cardiometabolic disease and certain cancers. Delayed sleep phase can occur in those exposed to bright light before falling asleep at night or night shift nurses exposed to daylight while trying to sleep during the day.

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