A special case for sheltered side being out like a light (6)
'out like a light' is the definition.
I can't tell whether this defines the answer.
'a special case for sheltered side' is the wordplay.
'special' becomes 'sp'.
'case for' indicates putting letters inside.
'sheltered side' becomes 'lee' (as in lee side, the side sheltered from wind).
'sp' going around 'lee' is 'sleep'.
'being' acts as a link.
Can you help me to learn more?
(Other definitions for asleep that I've seen before include "Like kippers", "this fast?", "in bed?", "Dead to the world", "Please be at rest, oddly".)