How to Test Light-Emitting Diodes (LEDs) with a Multimeter
Light emitting diode (LED) is a type of light emitting device that directly injects current. It is the result of the emission of photons when stimulated electrons inside a semiconductor crystal return from a high energy level to a low energy level, which is commonly known as spontaneous emission transition When a forward bias is applied to the PN junction of an LED, the injected minority carriers and majority carriers (electrons and holes) recombine and emit light It is worth noting that for a large number of particles at high energy levels, they spontaneously emit a column of light waves with an angular frequency of ν=Eg/h, but there is no fixed phase relationship between the columns of light waves, and they can have different polarization directions. The light emitted by each particle propagates in all possible directions, and this process is called spontaneous emission The emission wavelength can be represented by the following equation:
λ(μm)=1.2396/Eg(eV)
Light emitting diodes (LEDs) are generally made of materials such as gallium arsenide and gallium phosphide. They have a PN junction inside and also have unidirectional conductivity. However, LEDs emit light when conducting in the forward direction, and the brightness of the light increases with the increasing conduction current. The color of the light is related to its wavelength.
Universal meter testing method for ordinary light-emitting diodes:
Measure in R × 10K range with Fluke digital multimeter
Using a pointer multimeter with a 10k Ω range can roughly determine the quality of the light-emitting diode. Under normal circumstances, the forward resistance of a diode ranges from tens to 200k Ω, while the reverse resistance has a value of ∝. If the forward resistance value is 0 or ∞, and the reverse resistance value is very small or 0, it is prone to damage. This detection method cannot physically observe the light emission of the light-emitting tube, as the 10k Ω range cannot provide a large forward current to the LED.
