Agreed dodgepot, but I was referring to the fact that it could belong to either the 15 misprints or the extra letters clues. I had it in the wrong set that had me puzzled for a while. Otherwise, it is a very fair clue.
Lumen
39a - definition first 2 words; last word has extra letter
28d - misprint clue; definition is last word. Neither the answer, nor the first 4-letters of the wordplay, were familiar to me.