Arduino Uno + Light Sensor

Other Hardware Robotics
5 
  byte aa,bb;

Uninitialized local variables.

  float light = aa;
  float light2 = bb;

Now, the garbage is a pair of floats.

  Serial.print("Voltage=");
  Serial.print(light,1);
  Serial.print(light2,1);

The garbage does NOT correspond to voltage. You have NOT read anything from the sensor.

This is our code:
But were not quite sure exactly how it works

It doesn't.