We propose a Linear Irregular Fresnel Lens (denoted as LIFL) to replace the diffusion sheet and prism sheet in a rectangular LED-based Direct-type Backlight Module. The aim is to improve the illuminance and uniformity of LCD panel, as well as to reduce the cost of Backlight Module and make the Module thin. Here "Linear" means the grooves of a Fresnel lens are arranged linearly and "irregular" means that the sequence of all groove angles is not increasing or decreasing. To let the designed LIFL possess good effects of light ray guiding, two layers of LIFLs are needed. The first layer LIFL consists of x-axis grooves, whereas the second layer LIFL consists of y-axis grooves to guide all light rays guided by the first layer LIFL. The groove angles of the designed LIFL are evolved by a Genetic Algorithm which is developed in terms of the performance requirement on illuminance and uniformity of LCD panel in a rectangular LED-based Direct-type Backlight Module. In this paper, we will simulate a simple fifteen-LED Direct-type Backlight Module to demonstrate the performances on illuminance and uniformity of the designed LIFL.

No abstract