What is a simple way to measure the ambient light?
Perhaps a LDR and a 10k ohm resistor might work.



#define LDRpin A0
unsigned int LDRvalue = 0;

void setup(){
  Serial.begin(9600);
}

void loop(){
  LDRvalue = analogRead(LDRpin);
  Serial.println(LDRvalue);
  delay(1000);
}