Detector on E.g. a Lamp to Switch Off in Daylight

This page is the CodyCross answer for the clue below from Campsite Adventures, Group 840, Puzzle 3 (Nocturnal Creatures).

Question is: Detector on E.g. a Lamp to Switch Off in Daylight

and the answer is: SENSOR

Word Meaning:

SENSOR — A device or organ that detects certain external stimuli and responds in a distinctive manner.

Definitions from Wiktionary.