The main parameters of LED light source are VF and if, and other related parameters are color / color temperature / wavelength / brightness / luminous angle / efficiency / power consumption, etc. LED is a PN junction diode, which can conduct current only when sufficient forward voltage is applied. VF forward voltage is to establish a normal working state for LED light-emitting. If forward current is to promote LED light-emitting, and the brightness of light-emitting is in a positive proportion to the current flowing. VF nominal voltage of white LED: 3.4V ± 0.2V. In mass production of LED light source, VF of each batch of LED has certain discreteness. In order to meet the needs of customers, the LED must be sold in different VF grades when leaving the factory; otherwise, the brightness of LED lamps produced in the same batch will be different; the working current of LED if is selected according to the application needs, and different current grades cannot be mixed.