The unclued lights are of a specific kind. Additionally each is a legitimate inflected headword in Chambers. Elsewhere, ignore one acute accent and an apostrophe.
 

Across

 
4    By the way, black weapon is a valuable curio (9, two words)
9    C.O.O.L.E.R. characters in the mail? (10, two words)
12    Types of lenses — 1000 nice ones distributed (7)
14    Undertaking in 1A is cut by Harpagon (5)
16    Difficulty with butlers at heart will annoy (6)
21    Puss goes to and through such a passage (8)
22    Means to an end suggests food and games (7)
24    Reduced money for lounge...