Controlling LED's Using Ultrasonic Distance Sensor

#define Trigpin 7
#define Echopin 8
#define low_led 9
#define high_led 10
float distance;
int duration;
int ll = 700;

void setup() {
  pinMode (Trigpin, OUTPUT);
  pinMode (low_led, OUTPUT);
  pinMode (high_led, OUTPUT);
  pinMode (Echopin, INPUT);
  Serial.begin(9600);
  Serial.println ("Welcome To Distance Meter");
  Serial.println ("Coded By Jevins Annson");
  digitalWrite (low_led, LOW);
  digitalWrite (high_led, LOW);
}

void loop() {
  digitalWrite(Trigpin, LOW);
  delayMicroseconds(2);
  digitalWrite(Trigpin, HIGH);
  delayMicroseconds(10);
  digitalWrite(Trigpin, LOW);
  duration = pulseIn(Echopin, HIGH);
  distance = duration * 0.034 / 2;
  delay (ll);
  Serial.println (" ");
  Serial.print ("Distance = ");
  Serial.print (distance);
  Serial.print (" CM");
  Serial.println (" ");

  if (distance>=30)
  {
    Serial.println ("Nobody Is Infront Of the Sensor");
    digitalWrite (low_led, HIGH);
    delay (500);
    digitalWrite (low_led, LOW);
    delay (500);
    digitalWrite (low_led, HIGH);
  }
  else 
  {
    Serial.println ("Someone Is Infront Of the Sensor");
    digitalWrite (high_led, HIGH);
    delay (100);
    digitalWrite (high_led, LOW);
    delay (100);
    digitalWrite (high_led, HIGH);
    delay (100);
  }
}