Calibrating the Photoresistor

/*
 *  Jung Min Yean
 *  04/02/19
 *  Learning How to Use a Photoresistor with LEDs
 */

 const int LedPin1 = 9;
 const int LedPin2 = 10;
 const int LedPin3 = 11;
 const int PhotoPin = A0;
 const int PotPin = A1;
 int PotVal = 0;
 int PhotoVal = 0;
 unsigned long timeStart = 0;
 int Max = 0;
 int Min = 1000;
 const byte Button = 8;
 byte ReadVal;
 int count = 0;

void setup()
{
 pinMode(LedPin1, OUTPUT);
 pinMode(LedPin2, OUTPUT);
 pinMode(LedPin3, OUTPUT);
 pinMode(PhotoPin, INPUT);
 Serial.begin(9600);
  digitalWrite(LedPin1, HIGH);
  delay(100);
  digitalWrite(LedPin1, LOW);
    calibrate();
}

void calibrate()
 {
  timeStart = millis();
  while (millis()-timeStart <= 5000)
  {
    PhotoVal = analogRead(PhotoPin);
    if(PhotoVal > Max)
    {
      Max = PhotoVal;
    }
    if(PhotoVal < Min)
    {
      Min = PhotoVal;
    }
  }
  Serial.print("The Max Value is ");
  Serial.println(Max);
 }

void loop()
{
  // test potentiometer
  // PotVal = analogRead(PotPin);
  PhotoVal = analogRead(PhotoPin);
  Serial.println(PhotoVal);
  delay (200);
  // Serial.print("      ");
  int MapVal = map(PhotoVal,Min,Max,255,0);
  MapVal = constrain(MapVal, 0,255);
  Serial.println(MapVal);
  analogWrite(LedPin1, MapVal);
  analogWrite(LedPin2, MapVal);
  analogWrite(LedPin3, MapVal);
}