Show outside food store added illumination (9)

I believe the answer is:

sidelight

I'm a little stuck... Click here to teach me more about this clue!

'added illumination' is the definition.
'sidelight' can be an answer for 'illumination' (I've seen this before). I am unsure of the 'added' bit.

'show outside food store' is the wordplay.
'show' becomes 'sight' (I've seen this before).
'outside' is an insertion indicator (some letters go outside others).
'food store' becomes 'deli' (short for delicatessen).
'sight' placed around 'deli' is 'SIDELIGHT'.

Can you help me to learn more?

(Other definitions for sidelight that I've seen before include "Additional or incidental information" , "One shines" , "An essential for car" , "Car part" , "Window" .)

I've seen this clue in the Sydney Morning Herald.

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