What is a type a lamp? How are LED tubes classified?

In the UL certification system, LED tubes are divided into three categories: type A, type B and type C. The so-called type a lamp tube refers to the LED lamp tube with built-in drive, which can directly replace the LED lamp tube of traditional T5 and T8 fluorescent lamps without changing the lamp structure and circuit. Therefore, type a lamp tube is often called "lamp tube compatible with ballast". The so-called type B lamp tube refers to the LED lamp tube with built-in drive. During replacement, the lamp circuit needs to be changed, and the alternating current is directly fed into the lamp tube by removing the ballast. The so-called type C lamp tube refers to the LED lamp tube driven externally. When replacing, it is also necessary to change the lamp circuit and replace the traditional fluorescent lamp ballast with the corresponding LED driving power supply. There are also so-called "two in one" lamps on the market, which are lamps that can be compatible with both traditional ballasts and direct AC input. These lamps need two sets of certification of type a+b, and the cost is relatively high.