1st of all we decided to use a photoresistance in order to collect the ambiant light.

Furthermore we are using a led strip of 12V so we needed to put a transistor.

We followed the following scheme.

We add at this scheme the photoresistance. 

If you want to create the same thing as we did follow the cable management.

int led = 9;           // the PWM pin the LED is attached to

int brightness = 0;    // how bright the LED is
int fadeAmount = 100000000;    // how many points to fade the LED by
int photocellPin = 0; // the cell and 10K pulldown are connected to a0
int photocellReading;

// the setup routine runs once when you press reset:
void setup() {
  // declare pin 9 to be an output:
  pinMode(led, OUTPUT);
  Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {

  
  // set the brightness of pin 9:
  analogWrite(led, brightness);

  // change the brightness for next time through the loop:
  brightness = brightness + fadeAmount;

  // reverse the direction of the fading at the ends of the fade:
  if (brightness <= 0 || brightness >= 255) {
    fadeAmount = -fadeAmount;

        photocellReading = analogRead(photocellPin);
  Serial.print("Analog reading = ");
  Serial.print(photocellReading); // the raw analog reading
  // We'll have a few threshholds, qualitatively determined
  
  if (photocellReading < 200) {
    Serial.println(" - Dark");
    brightness = 255;
    
  } else if (photocellReading < 500) {
    Serial.println(" - Light");
    brightness = 100;
    
  } else if (photocellReading < 600 ) {
    Serial.println(" - Luminous");
    brightness = 50;

  }  else if (photocellReading < 700 ) {
    Serial.println(" - More luminous");
    brightness = 20;
    
  
  } else {
    Serial.println(" - Very bright");
    brightness = 0;
    

  }
  Serial.print(brightness );
  delay(5);
  
  }
  // wait for 30 milliseconds to see the dimming effect
  delay(30);
}