Unclued lights (one of three words) are of a kind, as suggested by the title.
 

Across

 
7    Mostly stern examination (3)
11    African’s body to rest briefly (6)
13    One fitted into more extensive counter (7)
15    Entice to enter round dance (5)
16    Having only a small Kazakh coin, couldn’t visit restaurant? (5, two words)
20    Succeeded breaking lyre’s third string, once dismal (6)
21    Place of exile’s back in the black (5)
22    A pound short, issue pork pies in boxes (7)
27    Goes wandering through the Spanish city (7)
29    Less fattening lines include wood sorrel (5, hyphened)
30    With protein, a gram is effective (6)
32    Constant delay, reversing cannon (5)
34    Pressed to move along I muttered (6)
36    Seem upset a little, turning to froth (5)
37    Volume ten follows established standard (5)
38    Ultimate in torture by Roman governor is to pull out hair (7)
39    Managed in English, dealing with just part of the tongue (6)
40    Almost succeed in dance step (3)
41    Sign off as guitarist (11)
 

Down

 
1    United, little may go wrong in the end (10)
2    Revealing a Rossini libretto? (8)
3    From Earth, over time, rising view of the Sun? (9)
4    Rush to repair ailing-sounding American herbarium (12, two words)
5    In punt, a wrong helmet (7)
6    Mexican border disturbance cut short: well done (8, two words)
7    Fights objections: nothing in them (5)
9    Say, Lambeth Walk taken around city (6)
10    Speak rashly, but handily twice interrupted? (5)
12    Children receive slipper without restraint (6)
14    Inspired work will change the result? (12, two words)
21    Miss a very robust soldier’s back (9)
23    Perhaps those in class ‘King-Emperor’ shortly needing a son (8)
24    Swede with girl, one who was mesmeric (8)
28    They mark the channel, a depression between islands (6)
33    A made-up language finally dies? Shame (5)
35    Minstrel’s restricted range (4)
 
A first prize of £30 for the first correct solution opened on 27 July. There are two runners-up prizes of £20. (UK solvers can choose to receive the latest edition of the Chambers Dictionary instead of cash — circle the word ‘Dictionary’.) Entries to: Crossword 2219, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.