The brightness of the LED is proportional to the current. So using a constant-current power supply can stabilize the brightness of the LED lamp. If a constant-voltage power supply is used, the current will fluctuate when the load changes, which will affect the brightness of the LED.
In addition, the relationship between the resistance and voltage of the LED is not linear. Thus a slight deviation from the constant voltage power supply may cause the current to change drastically, thereby burning out the LED lamp. Therefore, in the LED driving circuit, the use of a constant-current power supply can better protect the LED.