Digital Device Light Emissions Increase Sleep Dysfunction

Blue light emitted from the screens of electronic devices suppress melatonin by activating intrinsically photosensitive retinal ganglion cells (ipRGCs), according to a new study.

Researchers at the University of Houston (UH, TX, USA) conducted a study in 22 patients in order to investigate whether melatonin level and sleep quality can be modulated by decreasing night-time input to ipRGCs. To do so, study participant wore short-wavelength blocking glasses for an average of three hours prior to bedtime for two weeks. All subjects wore an actigraph device to measure activity, light exposure, and sleep, and saliva samples were collected to assess melatonin content. The Pittsburgh Sleep Quality Index (PSQI) was administered to assess subjective sleep quality.


The ipRGC-mediated post illumination pupil response was measured before and after the experimental period. During measurement, light exposure was presented using a flash electrode ganzfeld stimulator, which included one-second and five-seconds of long and short wavelength light. Pupil diameter was measured before, during, and for 60 seconds following flash stimulation. Six-second and 30-second post illumination pupil response and area under the curve following light offset were then determined.

The results showed that after the experimental period, the pupil exhibited a slower redilation phase, resulting in a significantly increased 30 second post illumination pupil response to the one-second short wavelength light, and decreased area under the curve for both one and five-second short wavelength light, when measured at the same time of day as baseline. Concomitantly, nighttime melatonin levels rose by 58%, objectively measured sleep duration increased by 24 minutes, and the mean PSQI score improved from 5.6 to 3.0. The study was published on June 27, 2017, in Ophthalmic & Physiological Optics.

“The most important takeaway is that blue light at night time really does decrease sleep quality. Sleep is very important for the regeneration of many functions in our body,” said lead author Lisa Ostrin, MD, of the UH College of Optometry. “By using blue blocking glasses we are decreasing input to the photoreceptors, so we can improve sleep and still continue to use our devices. That's nice, because we can still be productive at night.”

Most digital devices such as laptops, cellular phones, and e-book readers provide apps that can reduce or filter out blue light entirely. The apps do nothing during daylight hours, but after sunset place a red overlay on the screen to change its color temperature, canceling out the negative effects of the blue light and decreasing glare. Most eBook readers, which are black and white, have built-in white-on-black or sepia options that are better than a white background.

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