A light guide for an LCD system has a light incident side, and is formed with a plurality of pattern structures. Each of the pattern structures has a pair of diagonally-disposed first points defining a first length therebetween, and a pair of diagonally-disposed second points defining a second length therebetween. The second length extends transverse to and crosses the first length. A ratio of the first length and the second length of one of the pattern structures adjacent to the light incident side is greater than a ratio of the first length and the second length of one of the pattern structures distant from the light incident side.