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)
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