The main difference between 3mm and 5mm infrared emission tubes lies in power density, welding difficulty, and market popularity.

Power density: Under the same power, a 3mm sized infrared emitter tube has a higher power density, which enables it to achieve infrared signal transmission over longer distances. In contrast, the power density of the 5mm size transmitting tube is relatively small, but it is relatively easy to operate during welding.
Welding difficulty: Due to the high power density, the welding difficulty of a 3mm size transmitting tube is relatively high. The 5mm size launch tube is relatively easy to operate during welding, which provides convenience for users.
Market Popularity: Currently, 5mm sized infrared emission tubes are more common in the market, which may be due to their convenience during welding and relatively low power density requirements.

In summary, the choice of which size of infrared emission tube to use depends on the actual application requirements. If you need to achieve long-distance infrared signal transmission and do not mind the difficulty of welding, you can choose a 3mm emitter tube. If considering the convenience of welding and the common 5mm launch tube in the market, a 5mm launch tube is a more suitable choice