A team over from Harvard Medical School have compared reading paper books and light-emitting e-readers before sleep, where they discovered that it took a whole lot longer to actually grab some shuteye with an e-reader, which indirectly leads to poorer quality of sleep and as a natural consequence, being more tired in the morning after. In fact, the experts claims that people ought to minimize the amount of light exposure in the evening, and that is probably very sound advice.
Blue light is a wavelength that is commonly found in smartphones, tablets, e-book readers and LED lighting, where it will work to disrupt the body clock, as well as slow down or even prevent altogether the production of the sleep hormone melatonin.