Power Saving Automatic Light Control

/*------------------------------------
Code by Aydin Gokce
Feel free to use.
ig: @aydinguy
6/17/2018
------------------------------------*/
//Assigns names to digital pins on the arduino
const int trigPin = 9; 
const int echoPin = 10;
const int lights = 11;

//Establish variables duration and distance to be used later in code
long duration; 
int distance;


void setup() {
//Establishes which functions are inputs and which ones are outputs
pinMode(trigPin, OUTPUT); 
pinMode(echoPin, INPUT); 
pinMode(lights, OUTPUT);
//Starts serial communication with baud rate 9600
Serial.begin(9600);  
}

void loop() { 
//starts off the values as LOW
digitalWrite(lights, LOW);
digitalWrite(trigPin, LOW);
delayMicroseconds(2);

/*Gives a 5v current for 10 microseconds which allows the HC-SRO4 to emit an ultrasound of 40,000 hz*/
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);

//sees the value that the echo pin returned
duration = pulseIn(echoPin, HIGH);

/*You need to multiply the duration by 0.034 because the speed of sound is 0.034 cm/microsecond and divide it by 2 because of the time it takes to go there and back*/
distance= duration*0.034/2;

/*If there is anything within 30 cm (door, you, or whatever) it gives the relay a current which closes the circuit allowing for the 120v to go to the lights*/
if(distance < 30){
  digitalWrite(lights, HIGH);
  delay(1800000);
}
else{
  digitalWrite(lights, LOW);  
}

}