About fifty are sighted flying, which makes one happy (8)

I believe the answer is:

delights

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'makes one happy' is the definition.
I can't judge whether this definition defines the answer.

'about fifty are sighted flying' is the wordplay.
'about' is an insertion indicator.
'fifty' becomes 'L' (Roman numeral).
'flying' indicates anagramming the letters (letters fly around into new positions).
'sighted' is an anagram of 'deights'.
'l' placed inside 'deights' is 'DELIGHTS'.

'which' is the link.

Can you help me to learn more?

(Other definitions for delights that I've seen before include "Pleasures; pleases" , "Slighted by pleasures" , "Transports" .)

I've seen this clue in the Evening Standard.

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