int ldr=A7;
int led=4;
void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
pinMode(ldr, INPUT);
pinMode(led, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
int sensor=analogRead(ldr);
Serial.print("ldr: ");
Serial.println(sensor);
if(sensor>400){
  digitalWrite(led, HIGH);
}
else{
  digitalWrite(led, LOW);
}
delay(500);
}