It's all about the light color and how much it is shining directly into your eyes. In addition to dimming screen brightness as much as possible I use
an app on my PC and
a CynogenMod setting on my smartphone to lower the color temperature to 3700K (giving everything a red tinge) and that definitely helps. My nighstand lamp also uses a bulb with warmer light color. Imho blue light frequencies shining directly into your eyes are the main culprit in scree-related sleep delay/hindrance.
I wish I had a Paperwhite, as my nightstand lamp is way brighter than I'd need to still be able to read on my Kindle Touch …