According to Spooner, cake layer light (7)

I believe the answer is:

sunbeam

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'light' is the definition.
(sunbeam is a kind of light)

I cannot understand how the remainder of the clue works.

(Other definitions for sunbeam that I've seen before include "Ray of solar light" , "Bright ray -- bus name (anag)" , "sheds a bit of light" , "Ray of natural light" , "Bright shaft of daylight" .)

I've seen this clue in The Guardian.

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