how to read analog value continuous with Serial.read()

Thanks, but after i remove the first if statement serial monitor displayed single analogvalue same the old.

const int ledPin = 13;
void setup() {
 
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);
  pinMode(9, OUTPUT);
}


void loop() {
   
  int sensorValue1 = analogRead(A0);
  int sensorValue2 = analogRead(A1);
  int sensorValue3 = analogRead(A2);
  int light_sensitivity = 500;
  int incomingByte;
  
    // read the oldest byte in the serial buffer:
    incomingByte = Serial.read();
  
  switch (incomingByte) {
    
    case 'a':
       Serial.println(sensorValue1);
       break;
    case 'b':
       Serial.println(sensorValue2);
       break;
    case 'c':
       Serial.println(sensorValue3);
       break;
    case 'H':
       digitalWrite(ledPin, HIGH);
       break;
    case 'L':
       digitalWrite(ledPin, LOW);
       break;
  }
    if (sensorValue3 < light_sensitivity) 
      {
        digitalWrite(9, HIGH);
      }
     else
      {
        digitalWrite(9, LOW);
        
      }
      delay(300);
    }