One boy's bright beams (4)

I believe the answer is:

rays

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'beams' is the definition.
(rays of light)

I don't understand the remainder of the clue.

(Other definitions for rays that I've seen before include "Beams from sun or moon" , "Sunbeams" , "shafts" , "Flat fish" , "Fish with wing-shaped fins and long tails" .)

I've seen this clue in the Evening Standard.

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