Why do children suddenly become afraid of the dark?

I presuming that most children do… or at least some children do… although I’m interested in your experiences; if this has happened to your children (or if you can remember yourself going through this) and when it happened…and obviously why?

I always said that I would never start leaving the light on for my children ‘what a waste of electricity!’ Hark! my son has recently turned four and has complained of not liking his room because it’s “scary” and he’s expressed to me that he doesn’t like the darkness…So…if I leave the light on..he’s less scared…

I wonder why this happens? Is it just a ploy to come and sleep in mum’s room (I don’t think so, although possible)… does he just not like his room? Is he really afraid of the dark or afraid of the room?

I have tried asking him detailed questions but I tend to just get…“it’s scary”... I’m particularly interested in any correlation between age and occurrence of this…