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