A circuit and method of reducing noises for improving quality of display in a liquid crystal display (LCD) system. The LCD system includes an LCD panel and at least one lamp. In operation the LCD system is supplied with a vertical synchronization signal and a horizontal synchronization signal. In one embodiment, the method comprises the steps of determining a lamp driving frequency for the at least one lamp responsive to the horizontal synchronization signal, and generating a lamp driving signal with the lamp driving frequency to be received by the at least one lamp for producing light, wherein the following formulae (1) and (2) are satisfied:.times..times..delta..times..times..gtoreq..delta..gtoreq. ##EQU00001## where H.sub.sync is the frequency of the horizontal synchronization signal in unit of (Hz); f.sub.lamp is the lamp driving frequency for the lamp driving signal in unit of (Hz); m, n=1, 2, 3, . . . , an integer; and .delta. indicates the permissible error of the lamp driving frequency.