[1] Kari T, Gadegaard J, S ndergaard T, Pedersen T G, Pedersen K. Reliability of point source approximations in compact LED lens designs. Optics Express, 2011, 19(S6): A1190–A1195

[2] Wu R, Xu L, Liu P, Zhang Y, Zheng Z, Li H, Liu X. Freeform illumination design: a nonlinear boundary problem for the elliptic Monge-Ampére equation. Optics Letters, 2013, 38(2): 229–231

[3] Parkyn W A. Design of illumination lenses via extrinsic differential geometry. Illumination and Source Engineering, 1998, 3428: 154– 162

[4] Ries H, Muschaweck J. Tailored freeform optical surfaces. Journal of the Optical Society of America A, Optics Image Science and Vision, 2002, 19(3): 590–595

[5] Oliker V. Geometric and variational methods in optical design of reflecting surfaces with prescribed irradiance properties. In: Proceedings of SPIE, International Society for Optical Engineering. 2005, 594207

[6] Wang L, Qian K, Luo Y. Discontinuous free-form lens design for prescribed irradiance. Applied Optics, 2007, 46(18): 3716–3723

[7] Bortz J, Shatz N. Generalized functional method of nonimaging optical design. In: Proceedings of SPIE, Nonimaging Optics and Efficient Illumination Systems III. 2006, 6338: 633805

[8] Wester R, Müller G, V ll A, Berens M, Stollenwerk J, Loosen P. Designing optical free-form surfaces for extended sources. Optics Express, 2014, 22(S2): A552–A560

[9] Benítez P, Mi ano J C, Blen J, Mohedano R, Chaves J, Dross O, Hernández M, Falicoff W. Simultaneous multiple surface optical design method in three dimensions. Optical Engineering, 2004, 43 (7): 1489–1502

[10] Ries H R, Winston R. Tailored edge-ray reflectors for illumination. Journal of the Optical Society of America A, 1994, 11(4): 1260– 1264

[11] Ong P T, Gordon J M, Rabl A, Cai W. Tailored edge-ray designs for uniform illumination of distant targets. Optical Engineering, 1995, 34(6): 1726–1737

[12] Davies P A. Edge-ray principle of nonimaging optics. Journal of the Optical Society of America A, 1994, 11(4): 1256–1259

[13] Bortz J, Shatz N. Iterative generalized functional method of nonimaging optical design. In: Proceedings of the Society for Photo-Instrumentation Engineers. 2007, 6670: 66700A

[14] Luo Y, Feng Z, Han Y, Li H. Design of compact and smooth freeform optical system with uniform illuminance for LED source. Optics Express, 2010, 18(9): 9055–9063

[15] Cassarly W J. Iterative reflector design using a cumulative flux compensation approach. In: Proceedings of SPIE, International Optical Design Conference. 2010, 7652(4): 76522L

[16] Wang K, Han Y, Li H, Luo Y. Overlapping-based optical freeform surface construction for extended lighting source. Optics Express, 2013, 21(17): 19750–19761

[17] Zhang W Z, Liu Q X, Gao H F,Yu F H, Free-form reflector optimization for general lighting. Optical Engineering, 2010, 49(6): 063003

[18] Mao X L, Li H T, Han Y J, Luo Y. A two-step design method for high compact rotationally symmetric optical system for LED surface light source. Optics Express, 2014, 22(S2): A233–A247