Some actual medical studies (primary sources) with different points of view:
Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness
Real life trumps laboratory in matters of public health
Reply to Zeitzer: Good science, in or out of the laboratory, should prevail
Managing Media: Reflections on Media and Video Game Use From a Therapeutic Perspective
Recognizing Academic Performance, Sleep Quality, Stress Level, and Mental Health using Personality Traits, Wearable Sensors and Mobile Phones
A tablet that shifts the clock
Ophthalmic and Physiological Optics