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. You need to add a nine volt transistor battery or a nine volt; 25 mA supply.