The most popular usage for this kit is to make your own nightlight; and you won't be limited to one of those dinky seven watt bulbs. You could also switch just about any appliance, either on or off, with either darkness or daylight.
Light sensitivity is adjustable over quite a range. The relay can handle up to 10 amps AC.

Specifications:

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You need to add a nine volt transistor battery or a nine volt, 25 mA or greater power supply.