The unclued lights (one of two words) can be arranged into two associated groups.

Across

1 Company accepts blame having mended harpsichord (7)

5 Pieces of cloth left in islands linked with Turks (7)

9 A jolt makes it open a little (4)

11 Mid-June physical is affected (9)

12 Check mutt beginning to bark (4)

14 Shadows and clouds initially moving from isles in the Clyde (6)

16 Carpet the setter after a fiddle (5)

17 Fabulist seen by river and waters ebbing (5)

20 Hot air rising from the room — with a bit of luck! (7)

21...