source: http://www.medicaldaily.com/why-you-sho ... poor-sleepAccording to a soon-to-be-published study in the journal Organizational Behavior and Human Decision Processes, blue light from a smartphone’s display screen can inhibit melatonin production, leading to a poor night’s sleep, and a decrease in work performance the next day.
The electric lights that illuminate from smartphones, blue light, are believed to be disrupting the nightly release of the hormone melatonin — a sleep aid — while activating neurons that boost alertness. Blue wavelengths, boost attention, reaction times, and mood, but they are the most disruptive at night, according to the Harvard Medical School. The artificial light throws the body’s biological clock — or, the circadian rhythm — out of sync, resulting in the deterioration of sleep quality.
Of course all led screens would cause such an effect, not only those in a smartphone, but also TVs or computer screens. Additionally energy efficient light bulbs, such as fluorescent lights and led lights also produce quite a bit of blue light; thus these forms of lighting can have potential negetive effects for our health.
One thing we can do in order to avoid having our sleep ruined is to "avoid looking at bright screens beginning two to three hours before bed." http://www.health.harvard.edu/newslette ... dark-side/
In other words, no TV, smartphones or computers immediately before bedtime... Read a book instead!