Lumen,
5d 4 letter abbreviation in a 4 letter anagram
30d 1st word is the definition, holding defines the wordplay
I am completely stuck on 25a and 23d. I only have 3 of the cyclic set, but the first I have seems to go into 13a but one of the clues preceding that has to be part of the set of six - and that is really confusing me. On top of all that, I can't work out 6a, 6d, 29a or 27d even though I have answers for all of them.