Like robinuth, I have nearly but not quite got it. I had only the first letter of 15A still to find, but this is now clear thanks to Mysterons ("Know what I mean? Say no more!"). However, I can't see how 15A ties in with the theme, nor can I quite fathom how *eight* unclued lights suggest homophones of *ten* of a set. 28D doesn't seem to belong to what I think could be the set of 10; if I am right, 38A comes first in the set, but it would not belong to the set if one were in, say, France.