What do you call a dancing sunbeam?

What's the word or phrase for what I'll call a dancing sunbeam? Think of a prism hanging in a window. As it swings, the light it scatters moves around the walls and floor of the room. For some reason the term "light spider" comes to mind, but I can't seem to find that usage anywhere. Is there another that I'm forgetting?

As a child in Yorkshire, England, I called it a jack-a-dandy (or jack o'dandy), but I'm not finding much dictionary support for that usage. Wiktionary says it's used in New Zealand. All the other dictionaries seem to just define it as a diminutive of "dandy", a foppish man.