I have a g scale roundhouse with 8 doors. I would like to use a photo resistor to tell when lights are on (hardwired from the track power) in order to operate individual servos which will mechanically open the doors.
any idea on the code.?
You are not giving us much to go on - but it should be fairly easy.
I presume a photo-resistor is the same as a Light Dependent Resistor. Just wire it up as voltage divider and use the Arduno ADC to measure the voltage. If the voltage is above or below your threshold do stuff.
Look through the examples that come with the Arduino IDE and you should find all you need to know.
If you have problems getting your own code to work, post a copy of it here with a good description of what it should do and what it actually does. The Thread planning and implementing a program may have some useful stuff.
...R