Something that can detect objects in extra darkness (5)

I believe the answer is:

radar

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'something that can detect objects' is the definition.
I can't tell whether this defines the answer.

'in extra darkness' is the wordplay.
'in' indicates a hidden word.
'RADAR' is hidden in the letters of 'extra darkness'.

Can you help me to learn more?

(Other definitions for radar that I've seen before include "Electronic detection system" , "Method for detecting distant planes, ships etc" , "Navigational aid" , "one sends out signals" , "Position detector using radio wave pulses" .)

I've seen this clue in The Hindu.

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