Smartphone Screen Time and Sleep

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Volume 13, Number 3

The blue wavelength of the light spectrum has the strongest impact on the human circadian rhythm. Particular photo-receptors in the eye, intrinsically photosensitive Retinal Ganglion Cells (ipRGCs), are particularly sensitive to blue light and provide signals to brain regions that affect the body’s clock. Blue wavelengths tend to decrease the production of melatonin, thereby suppressing delta brainwaves (associated with sleep) and increasing alpha brainwaves (associated with alertness), so exposure to “blue” in the evening has implications for sleep. Because maintaining overall synchrony in circadian patterns is important for health, exposure to “evening blue” may have a particularly negative impact on well-being. Disruption in sleep patterns increases difficulty with weight management, susceptibility to diabetes, vulnerability to depression, risk for other health problems, and cognitive and behavioral deficiencies.

Of course, electronic devices are an evening source of blue wavelengths for human beings. This is why most recommendations for good sleep hygiene advise limiting use of computers and televisions near bedtime. Evening use of another electronic device, the smartphone, has been increasing, and while the screen is smaller than is a television or computer screen, it still represents exposure to blue light.

Research recently published in the scientific journal PLOS ONE examined relationships between smartphone use around the bedtime hours and sleep quality. The research sample consisted of 653 adults enrolled in the Health eHeart study. Not surprisingly, longer average smartphone screen time during bedtime and sleep periods was associated with a longer time to sleep onset, poorer sleep quality, and decreased sleep efficiency (typically defined as a ratio of time asleep over time in bed).

A plausible explanation for the association of smartphone use around bedtime and poorer sleep quality is the blue light exposure that comes from the smartphone screen. However, it is also possible that persons not feeling sleepy or having trouble falling asleep are more inclined to use their smartphones. But if this is the case, a vicious cycle is likely reinforced in which the response to having trouble sleeping itself interferes with sleep.

The hour of bedtime and the hour after bedtime appeared to be the most critical window in which smartphone screen time was associated with poorer sleep. The take-home message from the study would be to cease use of one’s smartphone at least one hour before bedtime, and then avoid turning to it if one doesn’t readily fall asleep after going to bed.


Paul J. Hershberger, Ph.D.

… is a clinical health psychologist. He is Professor of Family Medicine and Director of Behavioral Science for the Family Medicine Residency Program, Wright State University Boonshoft School of Medicine. His clinical practice includes psychotherapy, consultation, and coaching.




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