You need to describe what you have connected to the Arduino, on which pins. You say that you are using PWM to light the LED, and then you say you are trying to read the voltage to the LED. You can't do both with the same LED.
You need to describe what you have connected to the Arduino, on which pins. You say that you are using PWM to light the LED, and then you say you are trying to read the voltage to the LED. You can't do both with the same LED.