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to get dark; to grow dark
to end (of a day, year, season, etc.); to come to an end; to close
to be sunk in (e.g. despair); to be lost in (e.g. thought); to be overcome with
夕方になって外の空が昏れてきました。
The sky is getting dark.
日が昏れてきたので帰った。
I went home because it was getting dark.
日が昏れる前に無事に家に着きます。
I arrived before it got dark.