Very large painted/stained glass?

I picked this up the other day - although i have no idea what i'm going to do with it. it's almost painted inside the glass or as part of the glass process as it seems very baked on. there is in iridescence to it which doesn't come across in the photo. i don't know what it was for either. the guy who sold it to me had two, but the other was broken. was this from some kind of a transome lightwell or what???