When bulbs come to life? (4)

I believe the answer is:

dusk

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'life?' is the definition.
The definition and answer can be both states of affairs as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for dusk that I've seen before include "Sundown" , "Eventide" , "Gloaming" , "Time of day after sunset" , "Dark twilight" .)

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

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