Some quite tricky clues, I thought, for the Spectator puzzle. Took me a bit of time to realise that the highlighted word, if added, would make the three triplets into legitimate quads.
I have completed just about all the grid but can't see the hidden theme word (and therefore the connection with the unclued lights) for the life of me. Am I barking up the wrong tree in thinking it's a three-letter word in the fifth row? If I'm right I fail to make the connection with all unclued lights.