int photocellPin = 0; // the cell and 10K pulldown are connected to a0
int photocellReading; // the analog reading from the sensor divider
int LEDpin = 11; // connect Red LED to pin 11 (PWM pin) (this is not needed to use the sensor but if you have one laying around it could add a cool affect! This can be bought at your local Radio Shack.)
int LEDbrightness; //

void setup(void) {
    Serial.begin(9600);    // We'll send debugging information via the Serial monitor so if you can read it   without using a led
}
void loop(void) {
    photocellReading = analogRead(photocellPin);
    Serial.print("Analog reading = ");
    Serial.println(photocellReading); // the raw analog reading
    // LED gets brighter the darker it is at the sensor
    // that means we have to -invert- the reading from 0-1023 back to 1023-0
    photocellReading = 1023 - photocellReading;    //now we have to map 0-1023 to 0-255 since thats the          range analogWrite uses
    LEDbrightness = map(photocellReading, 0, 1023, 0, 255);
    Serial.println(LEDbrightness);
    analogWrite(LEDpin, LEDbrightness);
    delay(500);        
}