what cable should I use for a photoresistor or light-dependent resistor (LDR) that is connected to an analog input in an arduino 5 meters away?
No, shielded cable. Microphone cable or any other kind of coax. Connect the shield to ground at the Arduino.
Cat5 is very cheap and will probably work adequately well.
Be prepared for a rapid degardation of the sensor, if it is permanently exposed to daylight.
thanks for sharing guys
Grumpy Mike: why cat 5?
Whandall: thanks for the heads up
Because it is cheap and being a twisted pair affords some screening at the same time.