I think basically they prefer being in the dark! Something to do with the cones in their eyes (read it somewhere but can't remember where) and they're more sensitive to some kind of light than others, and at different times of day. It's why they dig burrows or like houses/nesting boxes that are dark inside. Having said that, our Syrian is ok with normal lamp lights when he is out in the evening, and he's not too bad during the day on the rare occasions he is out during the day. I think at night though, they need darkness - their brain chemicals kick in during their night phase.
I don't know if there's any difference between dwarfs and Syrians but some Dwarf hamsters are out more during the daytime than Syrians I believe. Yours is probably a bit nervy and scared at the moment
