J.L.
Hi A., you mentioned you left a light on in the house, instead of doing that, put a night light onh in his room, better yet a fish aquarium, my kids all had one in their rooms, Stuffed animals in the dark take on a whole new look, dolls as well, my on;y thing with him being afraid of the dark, is him running in your room, which I'm going to asume is dark, I doubt that this is the only reason he is doing that, he's leaving a dark room and going to a dark room, try the night light and or the aquarium, and then see how he does, cause like you said you don't want your 18 month old doing the same thing. J. L.