void loop() {
  rightSensorValue = analogRead(A0); // read the pot value

  // map the sensor value from the input range (400 - 900, for example) 
  // to the output range (0-255). Change the values 400 and 900 below
  // to match the range your analog input gives:
  int brightness = map(rightSensorValue, 400, 900, 0, 255); 

  analogWrite(redLED, brightness);  // set the LED brightness with the result
  Serial.println(rightSensorValue);   // print the sensor value back to the serial monitor