The building which has the principal Buddha image at a Japanese temple usually has a circular dragon painting on the ceiling. I believe it’s there as a protector spirit.

That’s why there is sometimes a flashlight (torch) next to the altar. It’s not provided so you can check out how much money is in the collection box, it’s there so you can get a look at the ceiling dragon. Such buildings are typically quite dark, and you may not be able to see the ceiling at all without the flashlight.

I couldn’t even get a decent strobe-less photograph of this ceiling with an 8-second exposure.