int ldr_s =A1;
 int led =7;

 void setup()
 {
  Serial.begin(9600);
  pinMode(ldr_s, INPUT);
  pinMode(led, OUTPUT);


 }
 void loop()
 {
  int sensorValue = analogRead(ldr_s);
  Serial.print("voltage: ");
  Serial.println(sensorValue );
  if(sensorValue>400)
  {
   digitalWrite(led, HIGH);
  }
  else
  {
    digitalWrite(led, LOW); 
  }
  delay(1000);
 }