Arduino light sensor code.

lightSensor.ino

// The Threshold for turning on the light between 0 and 1024
// 0 means the light is always off and 1024 means it's always on.
// 900 seems to be a good value.
#define THRESHOLD 900

// Digital pins:
#define RED_PIN 9
#define GREEN_PIN 10
#define BLUE_PIN 11

// Analogue pins:
#define LIGHT_SENSOR_PIN 0

void setup(){
	// Set the red, green and blue pins to OUTPUT.
	pinMode(RED_PIN, OUTPUT);
	pinMode(GREEN_PIN, OUTPUT);
	pinMode(BLUE_PIN, OUTPUT);
	
	// Write the highest value to the pins of the light
	// because the polarity is oddly inverted.
	analogWrite(RED_PIN, 255);
	analogWrite(GREEN_PIN, 255);
	analogWrite(BLUE_PIN, 255);
}

int lightSensorValue = 0;
int isOn = 0;
void loop(){
	// Read the light sensor's values into a variable.
	lightSensorValue = analogRead(LIGHT_SENSOR_PIN);

	// Test if the light is dim enough and set isOn accordingly
	isOn = 0;
	if (lightSensorValue > THRESHOLD){
		isOn = 1;
	}else{
		isOn = 0;
	}

	// Write all 3 pins to the same value
	// Making it black or white.
	digitalWrite(RED_PIN, isOn);
	digitalWrite(GREEN_PIN, isOn);
	digitalWrite(BLUE_PIN, isOn);
}