A light driver and the controller and the driving method thereof are disclosed. The controller has a reference generating circuit which has a dimming signal converting circuit, a thermal signal converting circuit and a selecting circuit. The dimming signal converting circuit converts a dimming signal into a converted dimming signal and the thermal signal converting circuit converts the thermal signal into a converted thermal signal. The selecting circuit selects the smaller one of the converted dimming signal and the converted thermal signal and outputs a reference signal based on the selected smaller signal.