Communication devices and tablet computers with self-luminous backlit displays can cause melatonin levels to drop, making it much harder to fall asleep, researchers at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, Troy, New York, explained. The authors of the report explained that if you have not yet gone to bed when exposed to a luminous screen for long enough, you will probably delay your bedtime.

Their study has been published in Applied Ergonomics and is titled “Light level and duration of exposure determine the impact of self-luminous tablets on melatonin suppression”.

Melatonin, a hormone, is involved in regulating our circadian rhythm, our body clock. Fluctuations in melatonin levels influence on our desire to stay awake or go to sleep. During evolution, sunlight exposure determined what our melatonin levels were. Our bodies still respond to melatonin in the same way we did thousands of years ago. The difference today is that we now have other sources of light, which can upset our body clocks.

Studies have shown that disturbances in our circadian rhythm may lead to brain cell changes, and cause sleep problems in aging. Researchers at the University of Southern California found that circadian rhythm is much more important to life than had previously been suspected.

Research head, associate professor, Mariana Figeuiro and team set out to determine what the effects of self-luminous tablets might be on melatonin suppression. They observed and gathered data on 13 volunteers who used the devices to watch films, play games and read documents.

Prof. Figueiro said:

“Our study shows that a two-hour exposure to light from self-luminous electronic displays can suppress melatonin by about 22 percent. Stimulating the human circadian system to this level may affect sleep in those using the devices prior to bedtime.”

The melatonin suppression that occurred after exposure to the luminous tablet screen was similar to what one would expect after being exposed to normal sunlight, the researchers explained. In other words, the screen light makes the human’s body clock regress from nighttime-sleepy to daytime-alert mode.

Figueiro said “Based on these results, display manufacturers can use our model to determine how their products could affect circadian system regulation.”

The team says their findings should be used to encourage gadget, tablet, mobile phone and screen manufacturers to create more circadian-friendly products which could follow our sleep-awake patterns, rather than work against them.

Perhaps manufacturers could design tablets to help people with certain conditions and illnesses linked to lack of sunlight exposure, such as seasonal affective disorder (SAD), and sleep problems commonly experienced by seniors. Users could be receiving therapy for their condition while watching a movie, playing games, writing letters, or reading texts – much more fun that simply sitting in front of a light box. (SAD treatment involves sitting in front of a light box each day for one or two hours).