Dad turned light off (6)
I believe the answer is:
addled
'off' is the definition.
(I've seen this before)
'dad turned light' is the wordplay.
'turned' is an anagram indicator.
'light' becomes 'led' (light-emitting diode).
'dad' is an anagram of 'add'.
'add'+'led'='ADDLED'
(Other definitions for addled that I've seen before include "Baffled - rotten" , "Confused like infertile egg" , "Befuddled" , "Confused (wits); made rotten" , "spoilt" .)