I have a 163 5mm leds in parallel powered with 15v that needs to turn on when dark. What else would be required besides a NPN Transistor and a photocell to do this function?
A CdS light sensor is better than a "photocell", and is the common method.
You don't need much more than a CdS snesor, any small signal NPN transistor and a few resistors, maybe a cap.
That type of control will slowly light the leds over half an hour as it gets darker. If you want the leds to snap fully on you need another NPN transistor and one more resistor, to add a "schmidt trigger" hysteresis effect.
I have a 163 5mm leds in parallel powered with 15v that needs to turn on when dark. What else would be required besides a NPN Transistor and a photocell to do this function?
an easier way is to use transistors-arrange two as a schmidt trigger and an extra one for switching your leds....bc547s etc may do,depending on the load you are going to switch...