LED, the light-emitting diode, is a solid-state semiconductor device that can convert electricity directly into light. The heart of LED is a semiconductor wafer. When the current acts on the chip through a wire, the electrons and holes are pushed into the quantum well, the electrons in the quantum well are combined with the holes, and then the energy is emitted in the form of photons. According to different forms, the classification of LED is also varied. Currently, most of them are classified according to the following four forms.

1. according to the luminous color of the light emitting tube

According to the light emitting tube, it can be divided into red, orange, green (and subdivided yellow green, standard green and pure green), blue light and so on. In addition, some light-emitting diodes contain two or three colors of the chip.

The light emitting diodes can be divided into four types, which are colored transparent, colorless transparent, coloured, colored and colorless. The scattered light emitting diode is used as a indicator light.

2. the characteristics of the light surface by the light emitting tube

According to the characteristics of the light emitting tube, the circular lamp, the square lamp, the rectangle, the LED panel, the light emitting tube, the side tube, the surface mounted miniature tube, etc. A circular lamp is divided into 2mm, 4.4mm, [Phi] 5mm, [Phi] 8mm, [Phi] 10mm, and [Phi] 20mm, and so on. The light emitting diodes of [[Phi] 3mm are usually recorded as T-1, and 5mm is recorded as T-1 (3/4).

The angular distribution of the circular luminous intensity can be estimated from the size of the half value angle. There are three categories from the angular distribution of luminous intensity:

(1) high directivity. Generally, it has a pointed epoxy package or a metal reflector cavity package without scattering agent. The half value angle is 5 to 20 degrees or smaller. It has high directivity and can be used as a local lighting source or combined with a light detector to form an automatic detection system.

(2) standard type. Usually used as indicator lamp, its half value angle is 20 ~ 45 degrees.

(3) scattering type. This is a larger indicator lamp with a half angle of 45 to 90 degrees or larger and a larger amount of scattering agent.

3. according to the structure of the light emitting diode

According to the structure of light emitting diode, it has full epoxy encapsulation, metal base epoxy encapsulation, ceramic base epoxy packaging and glass encapsulation.

4. according to the intensity of luminescence and the working current

LED (luminescence intensity <10mcd) with ordinary brightness according to the intensity of light intensity and working current; LED of ultra high brightness (>100mcd); high luminance LEDs with light intensity between 10 and 100mcd. The working current of general LED is from more than 10 mA to dozens of mA, while low current LED working current is below 2mA (brightness and ordinary) The same light emitting tube)

These are four more common types of LED classification, and each enterprise or manufacturer that uses LED as a raw material for production may use a different classification method.