I've used an LDR in series with a 47K resistor to do what you are describing and it worked well, but without specifics on your actuator, relays, Arduino and other components, thats about all I can say.
I've used an LDR in series with a 47K resistor to do what you are describing and it worked well, but without specifics on your actuator, relays, Arduino and other components, thats about all I can say.