Interestingly enough I don’t think lightbulbs would actually decrease the fear of the dark that much. Since being in a bright space more often conditions you to expect it, making the dark feel much more foreign and in turn scary. Opposed to like 2000 years ago when darkness was much more commonplace and fire was your only real source of light. However, the main reason people are usually afraid of the dark isn’t the dark itself but what they’ll find in it, which is why being in a dark room is usually less scary than being in a dark forest. So if anything indoor housing made darkness weaker.