Use a multimeter to determine the polarity of the semiconductor diode: usually use the ohm range of the multimeter (R*100 or R*1K), and then use the two test leads of the multimeter to connect to the two poles of the diode.
When the diode is on, measure The resistance value is small (usually between tens of ohms to several thousand ohms), then the black test lead is connected to the anode of the diode, and the red test lead is connected to the cathode of the diode.
When the measured resistance is very large (generally several hundred to several thousand ohms), then the black test lead is connected to the cathode of the diode, and the red test lead is connected to the anode of the diode.
