the invention provides a gray level control method for outputting a total gray level during a total period , including : dividing the total period into m unit periods ; alternatively outputting a gray level “ 0 ” or a selected gray level during each unit period ; and integrating the gray levels output during the m unit periods to obtain the total gray level , wherein during each of n successive unit periods of the m unit periods the selected gray level is a first gray level , and during each of the remaining unit periods the selected gray level is lower than the first gray level .