Backup Lamp Circuit

  
This little circuit will pay for itself many times over the first time it is used, especially if you are in the shower. This back-up lamp stays off as long as light falls on the CdS photocell from either the NE-2 or from room ambient light. So, if the power fails at night, the lamp will light.
Backup Lamp Circuit - schematic

The 6 volt lamp should be directed away from the photocell to achieve full brightness and the 1 meg. resistor may be varied to adjust the sensitivity. Most N-channel power fets such as the VN-67 will work if they turn on well with 6 volts. The NE-2 may be placed directly on top of the cell but make sure the leads do not touch other conductors. This design is safe and portable but it must be turned off at night when not in use. Alternately, neon night lights are available which could be used in place of the NE-2. These little round night lights won't burn out like the 7-watt incandescent bulbs which would result in unnecessary battery drain. The standby lamp may be built into an empty jar with the photocell shielded from the lamp. Place the jar close to the night light to turn off the standby lamp when the room is dark. This version may be freely carried away like an electronic candle since the nightlight is not mechanically connected.



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