If your LED beads do not light up when measured, there are several possible reasons. Here are some troubleshooting steps and suggestions to help you figure out what the problem is:
1. Power supply voltage: Check whether the voltage of the power supply meets the requirements of the LED. Typically, a single white or blue LED operates at about 3V to 3.6V, while a red or yellow LED operates at about 1.8V to 2.2V.
2. Current Limit: LEDs require the proper amount of current to operate properly. If there is not enough current, or if too much current causes the LED to burn out, the LED may not light up. Typically, an LED needs to pass about 20mA of current to reach its rated brightness. Make sure the circuit contains a suitable current limiting resistor.
3. Polarity: LEDs are diodes with positive and negative polarity (anode and cathode), so they must be connected in the correct direction. If the connection is reversed, the LED will not emit light. The anode (long leg) should be connected to the positive side of the power supply, and the cathode (short leg, usually marked with a notch next to it) should be connected to the negative side of the power supply.
4. Damaged LED: If the LED has been damaged, it will not glow. This may be due to overvoltage, overcurrent, thermal damage or other physical damage.
5. Circuit Problems: Please check whether other components in the circuit, such as resistors, capacitors, etc., are faulty, and whether the connections are firm.
6. Test equipment: Make sure your test equipment (e.g. multimeter) is in good working order and set up correctly (usually use the diode setting or low voltage setting for testing).
7. Ambient Light: In bright environments, it is sometimes difficult to observe the faint glow of the LED. Try testing the LED again in a darker environment.
If you are still unable to determine the problem, try the following: Test with a known intact LED to confirm that your test method and circuit are correct. Try a different power supply or battery. Test the continuity of the LED to confirm that there is no open circuit inside the LED. We hope this information helps you to solve your problem! If there are any other questions, please feel free to ask.