Put on light that's off (6)
I believe the answer is:
addled
'off' is the definition.
(I've seen this before)
'put on light' is the wordplay.
'put on' becomes 'add' (as in adding something on).
'light' becomes 'led' (light-emitting diode).
'add'+'led'='ADDLED'
'that's' is the link.
(Other definitions for addled that I've seen before include "mixed-up" , "turned bad" , "Scatterbrained like bad egg" , "Dad led (anag.)" , "spoiled" .)