In this paper, we propose a new composite ray mapping method to design freeform total internal reflective (TIR) optics for LED illumination. We sample the ray intensity distribution into rectangular grids which have the best topological match to those rectangular grids on the target surface. With the multiple-to-one mapping relationships between the source intensity distribution and target irradiance distribution, we can construct the freeform TIR surfaces and freeform refractive surface using Snell's law. Compared to our previous design using uv-θΦ composite ray mapping method, this design approach is expected to have much less surface error and improve the illumination uniformity further because of the better topological match, In addition, due to the overlapping mechanism by multiple-to-one (composite) ray mapping, the method could lead to a more robust freeform optics compared to traditional freeform optics designs.
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