Low source of luminance in darkness? Yes and no (9)

I believe the answer is:

moonlight

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'yes and no' is the definition.
I can't tell whether this definition defines the answer.

'low source of luminance in darkness?' is the wordplay.
'low' becomes 'moo' (both can mean to make a cow noise).
'source of' says to take the initial letters (the start - or source - of the word).
'in' is an insertion indicator.
'darkness?' becomes 'night' (night is a period of darkness).
The first letter of 'luminance' is 'l'.
'l' put inside 'night' is 'nlight'.
'moo'+'nlight'='MOONLIGHT'

Can you help me to learn more?

(Other definitions for moonlight that I've seen before include "work illegally" , "Burn the midnight oil" , "Perform work at night" , "Work late" , "Beethoven composition for piano" .)

I've seen this clue in The Guardian.

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