InoLab: Reading a Photoresistor

const int sensorPin = 0;
const int ledPin = 9;
int lightCal;
int lightVal;
void setup()
{
pinMode(ledPin, OUTPUT);
lightCal = analogRead(sensorPin);
}
void loop()
{
lightVal = analogRead(sensorPin);
if (lightVal < lightCal - 50)
{
digitalWrite(9, HIGH);
}
else
{
digitalWrite(9, LOW);
}
}