First, the chip emits heat and transmits the heat sink through the substrate. The heat sink then dissipates heat through the heat sink surface where the fins are located. Therefore, the size and area of the heat sink determine the efficiency of the heat sink.
In order to increase the area, it is generally formed into various shapes such as a column shape and a mesh shape. Because of such a complicated process, it cost relatively high. Thus, many factories cut corners and shoddy in order to save costs.
How to judge whether a factory is shoddy? The most direct way is to test whether the temperature of the chip is too high. In the terminology, this is called "junction temperature", which is the temperature of the PN junction of the LED. As long as the junction temperature is controlled within an acceptable range, the quality is passed. On the contrary, it is to cut corners.
Temperature measurement can only be carried out by professional factories with professional equipment, and it is impossible to test the thermometer.