In recent years, LEDs were applied to general lighting in large volume, mostly in territory of backlight lighting.
Therefore, our research would focus on backlight lighting.In this paper, one method was adopted to obtain freeform
surface with non-axial symmetry. Then by the freeform lens constructed by us, we would make the light field intensity
more uniform. At the second part of the paper, we would utilize heterogeneous micro lens array (MLA) to approximate
the shape of the freeform lens, and adjust the curvature radius and size of the micro lenses, and the arrangement way of
the micro lens by the simulation results. Through repeated trials, we could achieve a uniformlight intensity of LEDsusing
microlenses and the thickness of direct-lit backlight unit is 2 mm thick.