Night Time Fears - Fear of the Dark

My son is a sensitive little boy. We been co-sleeping for 3 years and recently started him on his own room. The start was not bad. Yes he would come into our room sometime in the night, but quietly and we do not discourage it. Lately however he stopped coming to our room quietly and is crying loud in his bed most of the time also wet with pee. When asking what is wrong that moment or during day time he would say he is afraid, afraid that it is dark (his closet light is on during the night). Question: how have you helped your kid to overcome their fears of the night/dark?