Unclued lights form three sets of three, each set related in a different way to a theme-word which is hidden in the grid and should be highlighted.
 

Across

1    Keeping on certain subject, I am an unusual scientist (13)
9    A court’s brief shade (4)
14    Mount paintings an artist submitted (6)
15    In position, mark hit (5)
20    Small holes in stone column you replaced (7)
21    Good money made, half in Oldie (7)
23    Risky amount to carry on horse (7)
24    Swimming organ, cold, leads to pains (5)
25    Recently winged (5)
26    Comparable condition, yet I lag badly (7)
32    Stupid-sounding right-winger in his element? (7)
36    Fighter KOs...