What is the function of LED VF voltage?

Vf of LED indicates the forward voltage drop of led.

Our common LED used as indicator light has Vf of1.7V; ; LED for lighting, usually 3V.

Knowing the Vf of LED,

1, online and offline multimeter (diode file of digital multimeter) can be used to judge whether it is good or bad;

2. When designing the circuit, knowing Vf, we can calculate the parameters of other circuit components according to this voltage drop. For example, the resistance of LED current limiting resistor.