Circuit Project:12v Light / Dark Switch

Often, for certain low
voltage lighting systems; you would like to turn off the lights during
the bright light of the day. Most commercial day/night switches are
designed for AC lighting. This hobby circuit below was designed for a
12v DC system. But, it could be modified for other voltage as well. It
uses an inexpensive photo-transistor as the light detector. An
n-channel FET is used to switch power to the
lights. A transistor circuit is included to provide some hysteresis.
This keeps the circuit from fluttering the light during the transition
from day to night and night to day. It is recommended that a plastic
tube be placed over the transistor to prevent it from being illuminated
by the lights it is controlling. By selecting the appropriate power FET, the circuit could control over 100 watts worth of 12v lighting. (July 22, 2008)

Source: DiscoverCircuits

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