The title suggests a pair of unclued lights which identify the common feature of the others. Solvers must shade the pair. Elsewhere, ignore an apostrophe.
 

Across

5 Protozoon seen wriggling aboard steamboat (6)
9 Water envelops very soft body part (10, two words)
14 One lacking time and place for study (3)
16 Piebald from Golden State I start to canter on (6)
17 Refuse in Derry collected by Bonfire night (5)
18 To take clothes off is wrong without hot temperature (5)
22 Tepid daughter is not after libertine (7)
25 Street of aged colonnades (5)
26 No longer restrain one relapsing lunatic (5)
28 Languages Marconi deployed (7)
31 Ruin behind village school (7)
33 So-called mimic accepted by drama school finally (7)
38 Birds circling Channel island love nesting (5)
39 Exclusive party a pair of lemons gatecrash (6)
40 Ceramicist’s china (3)
41 Fez trainee lost? It should be in the car (10)
 

Down

1 Prolixity tainted usurer’s slogan (13)
2 A sister stores it for aged relative (5)
3 Vatican notices rude gestures (6, hyphened)
4 Lady’s smock has light red colour (5)
6 Lakes stocked with silver fish (7)
7 Nine nursed by priest take nostrum (6)
10 Pass by famous frog (prince not king) (6)
11 Twice I left Mike jittery about old working system (9)
12 Daring grooms presenting cleaning tools (13)
13 Star keeps humming tune till now (8)
19 Blessed ladies die worshipped (9)
21 Sons row off progressing spectacularly (8)
23 Trial has speeding European imprisoned (7)
27 Servant unknown to whip animal (7, two words)
29 Painting with loaf and fruit (6)
30 Glass of very good whisky swallowed (6)
32 A criminal snubbed rakish policeman (6)
34 Fruit machine very small saint shuns (5)
35 Cricket enthrals English composer (5)
36 Noble look (4)
 
A first prize of £30 for the first correct solution opened on 1 December. There are two runners-up prizes of £20. (UK solvers can choose to receive the latest edition of the Chambers Dictionary instead of cash— ring the word ‘Dictionary’.) Entries to: Crossword 2238, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.