A measure of enlightenment (11)

I believe the answer is:

candlepower

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'a measure' is the definition.
(candlepower is a kind of measure)

I don't understand how the remainder of the clue works.

(Other definitions for candlepower that I've seen before include "Measure of luminosity" , "Measure of light emitted" .)

I've seen this clue in The Globe and Mail.

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