1. Speaker: Bo-Wen Xiao ( 蕭博文 ) Advisor: Prof. Yi-Pai Huang ( 黃乙白教授 ) Prof. Chung-Hao Tien( 田仲豪教授 ) Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu, Taiwan Oct. 13 2008 LEDs-based Flat Lighting Device for LCD Backlight Applications LEDs-based Flat Lighting Device for LCD Backlight Applications

2. 2 Advanced Display Optics Lab Outline  Introduction - Conventional White LED Backlight - Visible Light Excited Phosphor Sheet Backlight  Motivations & Objectives  Simulation Model & Experimental Results  Conclusions & Future Work

3. 3 Advanced Display Optics Lab Introduction Conventional white LED backlight Reflector point light source planar light source Blue LED chip Substrate YAG phosphor Reflector YAG phosphor Blue LED chip packaged inside device coated on external substrate (Roll-to-roll process) VEPS backlight (Visible Light Excited Phosphor Sheet) proposed by Kismart Co. diffuser must be installed point light source light-redistributed Diffuser

4. 4 Advanced Display Optics Lab Mixed white light Incident blue light Excited Lambertian yellow light Diffused blue light Light Redistributed Mechanism in VEPS (blue light  excited yellow light) YAG-phosphor layer Diffuser Wavelength converter Visible blue light (blue light  diffused blue light) YAG Phosphor Substrate Blue LED Chip Reflector Roll-to-roll process Light-redistributed mechanism  large-sized display  thin-thickness display VEPS has the potential for fabricating ultra-slim backlight for large-sized LCD-TV applications. VEPS has the potential for fabricating ultra-slim backlight for large-sized LCD-TV applications.  high brightness uniformity  high coating uniformity

5. 5 Advanced Display Optics Lab Outline  Introduction - Conventional White LED Backlight - Visible Light Excited Phosphor Sheet Backlight  Motivations & Objectives  Simulation Model & Experimental Results  Conclusions & Future Work

6. 6 Advanced Display Optics Lab Motivations  Light-redistributed mechanism is complex. Wavelength-converting process Blue lightYellow light Light-diffusing process Blue light Issue3: no simulation model to design and optimize Pitch Gap Issue1: mura effect Excited Lambertian yellow light Diffused blue light Issue2: angular color deviation

7. 7 Advanced Display Optics Lab Apply the simulation model to solve mura effect. Objectives Establish a simulation model of VEPS. Design an ultra-slim VEPS backlight for 42-inch LCD-TV. ( backlight module thickness ≦ 15mm ) Apply the simulation model to solve angular color deviation.

8. 8 Advanced Display Optics Lab Outline  Introduction - Conventional White LED Backlight - Visible Light Excited Phosphor Sheet Backlight  Motivations & Objectives  Simulation Model & Experimental Results  Conclusions & Future Work

9. 9 Advanced Display Optics Lab >95% <95% BTDF of YAG-phosphor layer blue light  excited yellow light BTDF of YAG-phosphor layer blue light  diffused blue light Correlation Coefficient Output Multi-chip VEPS module simulation model establishment Unit-chip VEPS module BTDF* measurement Flowchart of Simulation Model of VEPS *BTDF (Bidirectional Transmittance Distribution Function)  describes the light scattering characteristics of a surface

10. 10 Advanced Display Optics Lab BTDF Results of YAG-Phosphor Layer  Bidirectional transmittance distribution function (BTDF) blue light  diffused blue light blue light  excited yellow light close-to-Lambertian directional

11. 11 Advanced Display Optics Lab x y YAG-Phosphor Layer Blue LED Chips (5x5 chips) BTDFs applied Simulation model of multi-chip VEPS module Simulation Results of VEPS Module Reflector Uniformity measured area Pitch Gap Pitch Gap VEPS has higher uniformity than conventional backlight. Uniformity of VEPS > 80%, when gap > 10mm (pitch =10mm) Uniformity of VEPS > 80%, when gap > 10mm (pitch =10mm)

12. 12 Advanced Display Optics Lab Demonstrated Ultra-slim VEPS BL Slim VEPS module Reflector YAG-Phosphor Layer experimental result Blue LED chips 86.13% simulation result 86.17% Verify the accuracy of chromaticity and solve angular color deviation in the future. Verify the accuracy of chromaticity and solve angular color deviation in the future. Provide a platform to optimize pitch of LED chips to prevent mura effect successfully. Provide a platform to optimize pitch of LED chips to prevent mura effect successfully. x y

13. 13 Advanced Display Optics Lab Outline  Introduction - Conventional White LED Backlight - Visible Light Excited Phosphor Sheet Backlight  Motivations & Objectives  Simulation Model & Experimental Results  Conclusions & Future Work

14. 14 Advanced Display Optics Lab Conclusions  Visible Light Excited Phosphor Sheet Backlight (VEPS) has the potential for fabricating the ultra-slim backlight for the large-sized LCD-TV applications.  Mura effect and angular color deviation in VEPS needs to be solved.  Simulation model of VEPS provides a platform to optimize the pitch of LED chips and prevent mura effect.

15. 15 Advanced Display Optics Lab Future Work Excited yellow light Diffused blue light  Verify the accuracy of chromaticity of simulation model.  Design the ultra-slim VEPS backlight for 42-inch LCD-TV. ( backlight module thickness ≦ 15mm ) Optical sheet  Apply simulation model to solve angular color deviation.

16. 16 Advanced Display Optics Lab

17. 17 Advanced Display Optics Lab

18. 18 Advanced Display Optics Lab Roll-to-roll Coating Process Flow Phosphor In Phosphor Film Out PET Film In

19. 19 Advanced Display Optics Lab Definition of BTDF

20. 20 Advanced Display Optics Lab Spectrum Measurement Results Incident blue light Mixed white light

21. 21 Advanced Display Optics Lab VEPSConventional BL Simulation Results

22. 22 Advanced Display Optics Lab VEPS (pitch=10mm) Conventional BL (pitch=10mm) 83.01% 12.98% VEPS has higher uniformity than conventional backlight. VEPS has higher uniformity than conventional backlight. Simulation Results

23. 23 Advanced Display Optics Lab Exp. VEPS Exp. Conventional BL Simu. VEPS Simu. Conventional BL 86.13%86.17% 11.82%15.55% Exp. VS Simu.

24. 24 Advanced Display Optics Lab Changing Θ φ=0 φ=90 φ=180 φ=270 uv Θ= 00.1570.399 Θ=300.1590.433 Θ=600.1630.463 φ=0

25. 25 Advanced Display Optics Lab 0.10.20.30.40.50.60.0 0.1 0.2 0.3 0.4 0.5 0.6 0.0 uv (a) Θ= 00.1570.399 (b) Θ=300.1590.433 (c) Θ=600.1630.463 φ=0 uv (a) Θ= 00.1570.399 (b) Θ=300.1590.432 (c) Θ=600.1630.462 φ=90

26. 26 Advanced Display Optics Lab 0.10.20.30.40.50.60.0 0.1 0.2 0.3 0.4 0.5 0.6 0.0 uv (a) Θ= 00.1570.399 (b) Θ=300.1580.429 (c) Θ=600.1620.460 φ=180 uv (a) Θ= 00.1570.399 (b) Θ=300.1580.430 (c) Θ=600.1620.458 φ=270

27. 27 Advanced Display Optics Lab Conventional backlight using white LEDs VEPS Backlight (Visible Light Excited Phosphor Sheet) Diffuser

28. 28 Advanced Display Optics Lab Flow Chart of Simulation Model of VEPS Unit-Chip VEPS Module Unit-Chip VEPS Module BSDF Diffused blue light BSDF Excited yellow light Correlation Coefficient Correlation Coefficient Output

29. 29 Advanced Display Optics Lab Demonstrated Ultra-slim VEPS BL slim VEPS module Reflector YAG-Phosphor Layer VEPSModule combined with diffuser only Blue LED chips 86.13% 11.82%

30. 30 Advanced Display Optics Lab

31. 31 Advanced Display Optics Lab Simulation Results of VEPS BL Reflector x y YAG-Phosphor Layer Blue LED Chips (5x5 chips) Uniformity measured area BSDFs applied 12mm 80 mm Pitch Simulation model of multi-chip VEPS module VEPS Conventional BL

32. 32 Advanced Display Optics Lab x y YAG-Phosphor Layer Blue LED Chips (5x5 chips) BSDFs applied 12mm 80 mm Simulation model of multi-chip VEPS module Simulation Results of VEPS Module Reflector Uniformity measured area Pitch VEPS (pitch=10mm) Conventional BL (pitch=10mm) 83.01% 12.98% VEPS has higher uniformity than conventional backlight. VEPS has higher uniformity than conventional backlight.

33. 33 Advanced Display Optics Lab Pitch Gap VEPS has higher uniformity than conventional backlight. Uniformity of VEPS > 80%, when gap > 10mm (pitch =10mm) Uniformity of VEPS > 80%, when gap > 10mm (pitch =10mm)

34. 34 Advanced Display Optics Lab Motivations  Light-redistributed mechanism is complex. Wavelength-converting process Blue lightYellow light Light-diffusing process Blue light Issue1: no simulation model to design and optimize Pitch Gap Issue2: mura effect Excited Lambertian yellow light Diffused blue light Issue3: angular color deviation