The ten unclued lights (one of two words and hyphened) consist of two themes which can be resolved into five playful pairs. Elsewhere, ignore one accent.

Across

10 Source of painting old archdeacon found in spring (10)
12 Display and make lace as well (6)
13 Richard Murphy, it’s said, is a tyrant (8)
17 Tending to wear away motor-biker’s gear returned during middle of week (7)
18 Improve hospital in Cornish town with no parking zone (7)
20 Could be Oxford poetry at Globe (8)
25 Openings of saunas provided at resort (3)
26 Turn down the heat and look relaxed (7, hyphened)
28 Abominable chap, one...