This sketch reads the light intensity values from a photo-resistor connected to pin A0 of an Arduino.

light-sensor.ino

// the setup function runs once when you press reset:
void setup() {
        // initialize serial communication at 9600 bits per second:
        Serial.begin(9600);
}
// the loop routine runs over and over again forever:
void loop() {
        // read the input on analog pin 0:
        int sensorValue = analogRead(A0);
        // print out the value you read:
        Serial.println(sensorValue);
        delay(10);
}