Sleep researchers say that looking at a blue light, which is produced by smartphone and tablet screens, sets off brain receptors that are designed to keep us awake and interferes with circadian sleep patterns. Experimental research has found that if people use a tablet for up to two hours before bed, it takes an extra hour to fall asleep. via For a Restful Night, Make Your Smartphone Sleep on the Couch
Using the tablet for reading seems like a bad move just before bed. The article also suggested that having your smartphone as an alarm clock might be another reason to your insomnia.
Looks like I just found the reason why I am having problem sleeping at night. It’s time to leave the smartphone away from the bed and no more late night reading.