Not at home, prefer some illumination when asleep (3,4,1,5)
I believe the answer is:
out like a light
'asleep' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'not at home prefer some illumination' is the wordplay.
'not at home' becomes 'out' (out can mean away from home).
'prefer' becomes 'like' (I've seen this in another clue).
'some' becomes 'a'.
'illumination' becomes 'light' (synonyms).
'out'+'like'+'a'+'light'='OUT LIKE A LIGHT'
'when' acts as a link.
Can you help me to learn more?
(Other definitions for out like a light that I've seen before include "Having no problems sleeping" , "Quickly asleep" .)