Asymmetric Reflector with Free-form Curvature for Uniform Projecting Illumination Hao-Wen Chuang 1 ( 莊浩彣 ), Chien-Hsiang Hung 2 ( 洪健翔 ), Chung-Hao Tien 1 ( 田仲豪 ), Yi-Pai Huang 1 ( 黃乙白 ) Display Institute 1, Institute of Electro-Optical Engineering 2, National Chiao Tung University, Hsinchu, Taiwan 顯示科技研究所、光電工程研究所 國立交通大學 Dec. 6 th, 2008 OPT TICC, Taipei, Taiwan Optics & Photonics Taiwan 2008 Session: Sat-S42-05

2 ADO & OIS Lab.Hao-Wen Chuang Outline  Introduction  Objective of optical design  Design method of free-form reflectors Concept Mathematical form  Simulation results  Conclusions

3 ADO & OIS Lab.Hao-Wen Chuang Introduction to Reflective Display Billboard (Cholesteric Liquid Crystal Display) Reflective – Day: sunlight Night: front lighting Issues – nonuniform brightness, specular reflection, glare effect poor contrast

4 ADO & OIS Lab.Hao-Wen Chuang Objective of Luminaire Design  Objective – Uniform projecting illumination uniformity brightness

5 ADO & OIS Lab.Hao-Wen Chuang Reflectors Design of Luminaire Andreas Timinger et al. “Designing Tailored Free-Form Surfaces for General Illumination” Proc. of SPIE Vol (2003) Common reflectorFree-form reflector ShapeConic: paraboloid, ellipsoidal, spherical…etc. no rotational symmetry Design parameters simple analytical equations (a few parameters are used) more degrees of freedom  Conic reflector vs. Free-form reflector

6 ADO & OIS Lab.Hao-Wen Chuang Optical Design  Two-dimensional analysis illuminance on the target plane: uniform illuminance,  Target intensity distribution: The profile of the reflector’s shape is calculated analytically.

7 ADO & OIS Lab.Hao-Wen Chuang Outline  Introduction  Objective of optical design  Design method of free-form reflectors Concept Mathematical form  Simulation results  Conclusions

8 ADO & OIS Lab.Hao-Wen Chuang Design of Reflectors: Concept different radius of curvature  varying ray diverging ability flux conservation  diverging angle dθ’ Luminance can be adjusted by means of the diverging angle corresponding to the arbitrary curvature of the reflector. ΔΦ

9 ADO & OIS Lab.Hao-Wen Chuang Design of Reflectors: Mathematical Form curve of the reflector tangent vector unit vector of the reflected ray Weighting function ( is projected on the integrating sphere centered at the origin) R relationship between dθ and the light projected on the integrating sphere

10 ADO & OIS Lab.Hao-Wen Chuang Design of Reflectors: Mathematical Form Flux conservation I s : luminous intensity from source I’: target intensity purposed diverging distribution function C(θ)  Reflector curve function r(θ)

11 ADO & OIS Lab.Hao-Wen Chuang Outline  Introduction  Objective of optical design  Design method of free-form reflectors Concept Mathematical form  Simulation results  Conclusions

12 ADO & OIS Lab.Hao-Wen Chuang 100 cm  Ray-tracing Simulation Results  Profile of the reflector 30 cm Luminaire Target Plane

13 ADO & OIS Lab.Hao-Wen Chuang Simulation Results: Illuminance  Illuminance distribution <100 Lux Uniformity deviation: 2-D 1-D (vertical)

14 ADO & OIS Lab.Hao-Wen Chuang Uniformity & Efficiency Enhancement  Uniformity (free-form reflector & paraboloid reflector comparison)  Efficiency Enhancement CCFL directly illuminating on the plane: Free-form reflector: Illumination uniformity and efficiency is greatly improved with the proposed free-form reflector.

15 ADO & OIS Lab.Hao-Wen Chuang Outline  Introduction  Objective of optical design  Design method of free-form reflectors Concept Mathematical form  Simulation results  Conclusions

16 ADO & OIS Lab.Hao-Wen Chuang Conclusions We proposed a design method of reflector with free-form curvature for the purpose of uniform illumination. The designed reflector greatly improves the illumination uniformity and efficiency enhancement. Uniformity deviation is within 14%; efficiency enhancement is enhanced by nearly 5 times. Free-form reflectors allow more degrees of freedom for design for various lighting applications.

17 ADO & OIS Lab.Hao-Wen Chuang 17

18 ADO & OIS Lab.Hao-Wen Chuang Objective of Optical Design  Two-dimensional analysis illuminance on the target plane uniform illuminance,  Target intensity distribution

19 ADO & OIS Lab.Hao-Wen Chuang Design of Reflectors: Mathematical Form the curve of the reflector tangent vector of the unit vector of the reflected ray Weighting function ( is projected on the integrating sphere centered at the origin) R

20 ADO & OIS Lab.Hao-Wen Chuang Design of Reflectors: Mathematical Form Flux conservation I s : luminous intensity from source I’: target intensity relationship between dθ and the light projected on the integrating sphere purposed diverging distribution function C(θ)  Reflector curve function r(θ)

21 ADO & OIS Lab.Hao-Wen Chuang Parabolic reflector