Reactions explains why our smartphones won’t let us sleep. Smartphone displays send out a lot of blue light and out brain processes that blue light as being daytime outside and thus we won’t be able to sleep as fast as we’d want to.
Blue light interacts with melanopsin, a protein in the cells of our retina, which in turn signal the brain that it is daytime. And here is where the issues start. When you want to sleep, simply leave the phone be. Sleep tight.