In consideration of the development trends of backlights, a global dimming algorithm for side-lit backlights was proposed to solve the problems of Liquid Crystal Devices(LCDs) in low contrast ratio and high power consumption. The backlight dimming level was decided by the average luminance and the difference between the average and max grayscales of all subpixels. Then, the S-shaped function was involved to improve the static contrast ratio, by which the pixels with the grayscales more than the turning point of the curve could be become brighter and those less than the turning point could become darker, so that the static contrast ratio was improved efficiently. The algorithm was simulated and a prototype was developed to evaluate the effects of the dimming algorithm. Experimental results indicate that the power consumption of the LCD with the global dimming heavily depends on what to be displayed on the images. For 40 different kinds of images, the average power has reduced by 9.39% and the static contrast ratio improved by 124.7%. The side-lit backlights performing the proposed global dimming algorithm have the advantages of low-cost, small thickness, low power consumption and high constrast ratio.