Please switch illumination off! (7)
I believe the answer is:
delight
'please' is the definition.
(I know that please can be written as delight)
'switch illumination off' is the wordplay.
I cannot quite see how this works, but
'illumination' could be 'light' (synonyms) and 'light' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for delight that I've seen before include "Greatly please" , "Jubilation" , "It could be Turkish" , "Enjoyment" , "Lighted to give real pleasure" .)