Generally lighter across outskirts of Yeovil? (2,3,5)

I believe the answer is:

by and large

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'generally' is the definition.
('by and large' can be a synonym of 'generally')

I can't explain the rest of the clue.

(Other definitions for by and large that I've seen before include "In general" , "In the main" , "On the whole" , "for the most part" , "As a rule" .)

I've seen this clue in The Times.

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