Each of the eight unclued lights is a series of letters in alphabetical order which can be formed into eight theme words. Elsewhere, ignore two accents.
 

Across

1    Book from Goon, having siesta disturbed (12)
10    Second-in-command’s deviant practice (4)
12    Gave permission and reportedly went under, getting ignored (10)
14/40     French pal, tense, at heart in his city (6)
18    A lad — Tim — composed Dahl musical (7)
22    Fields entered by sportsmen, finally (6)
24    On outskirts of Evesham, encountered Cornish tourist (5)
26    Writers taking a fizzy drink in the Florida Panhandle (9)
27    See a trick re-presented by lutz performer (3-6)
29    Speedy aunt regularly appearing...