Chapter 6 Conclusions and Future Work
6.2 Future Work
We had already successfully developed the UFL and BFL systems which are suitable for the future backlight units with high brightness, slim format, and large display scale. However,
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local dimming technology is a trend in the current display market. The LCD‟s dynamic range can be effectively improved and the power consumption can be greatly reduced by controlling backlight individually[37,38,39,40,41]
. According to the research by C.H. Chen[42] in our laboratory, the Lorentz distribution is the most appropriate light spread function for the locally dimmable backlight systems. By applying the Lorentz distribution into each backlight division‟s output profile, the image quality can be improved in boundary perception.
The BFL system is a potential system for developing the local dimmable backlight units.
By controlling LED chips individually, the output pattern radiated from the YAG-phosphor layer can be adjusted. However, the uniform output profile should be revised before adopting the local dimming technology. Fig.6-1 shows the light distribution of the optimized BFL system. For single-chip illuminating case, the light distribution is closed to Lorentz distribution. For multi-chip illuminating case, the BFL system performed a uniform output profile. Nevertheless, such uniform distribution is narrower and the illuminating intensity on edge is lower than the Lorentz distribution. In other words, such output profile is not suitable for the locally dimmable backlight systems.
Fig. 6-1 Light distributions of the BFL system with blue LED chips illuminating in different numbers,
(b) 3-chips
(a) Single-chip
(c) 11-chips
Blue LED chips
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Therefore, in the future, we can embed a Fresnel lens structure into the BFL system to enlarge illuminating intensity on edges and further optimize the BFL system‟s output profile.
As shown in Fig. 6-2, by embedding a Fresnel lens between the blue LEDs and the YAG-phosphor layer, the edge-emitting lights can be redirected toward center and the luminance on the central position can be maintained.
By this method, the output profile of BFL system will be modified to Lorentz distribution. Thus, the BFL system will be appropriate for developing the locally dimmable backlight systems.
Fig. 6-2 Schematic configuration of the Fresnel lens embedded BFL system.
Blue LED Chip YAG-phosphor
Original Light Distribution Lorentz Distribution
Fresnel Lens
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Reference
[1] H.-T. Huang, C.-H. Hung, Y.-P. Huang, C.-H. Tien, C.C. Tsai, H.-P. D. Shieh, J. Lin, J.
Chen, P. Chen, and W.-C. Chang, “UV Excited Flat Lighting (UFL) System for LCD-TV Backlight Application,” SID‟08 DIGEST, p.862-p.865 (2008)
[2] B.-W. Xiao, C.-H. Hung, H.-T. Huang, J. Chen, Y.-P. Huang, C.-H. Tien, and C.C. Tsai,
“LEDs-based Flat Lighting Device for LCD Backlight Applications,” OPT‟08, Sat-S23-01 (2008).
[3] B.-W. Xiao, C.-H. Hung, H.-T. Huang, Y.-P. Huang, C.-H. Tien, C.C. Tsai, H.-P. D.
Shieh, J. Chen, J. Lin, and W.-C. Chang, “Optical Simulation and Analysis of Visible-light Excited Phosphor Sheet (VEPS) System,” IDMC‟09,Wed-P5-01 (2009).
[4] B.-W. Xiao, C.-H. Hung, H.-T. Huang, Y.-P. Huang, C.-H. Tien, C.C. Tsai, H.-P. D.
Shieh, J. Chen, J. Lin, and W.-C. Chang, “Optical Properties of Visible-light Excited Phosphor Sheet (VEPS) System,” SID‟09 DIGEST, p.1034-p.1037 (2009).
[5] E. Lueder, Liquid Crystal Displays, John Wiley & Sons, p.294 (2000)
[6] K. Käläntär, “Highly Light Collimating Unit for Realization of Mosaic Structure Large Size RGB Backlight,” IDW‟05, p.1273-1276 (2005)
[7] E. Lueder, Liquid Crystal Displays, John Wiley & Sons, p.121 (2000)
[8] J. Graf, G. Olczak, M. Yamada, D. Coyle and S. Yenug, “ Backlight Film & Sheet Technology for LCDs,” Seminar Lecture Note, SID‟08, p.M-12/6 (2008)
[9] C.-W. Chen, M.-C. Hsu, Y.-W. Fang, C.-C. Kuo, and K.-S. Wang, “The Advanced Algorithm for Band Mura Analysis and Quantification in LCD Panels,” SID‟09 DIGEST, p.706-708 (2009)
[10] A. Abileah, “Applications Tutorial A-2: Display Measurements of Flat-panel Displays,”
SID‟07 DIGEST, p.A-2/18 (2007)
[11] M. Schiavoni, G. Counil, P. Gayout, J.-L. Allano and R. Marandon, “Novel Glass Diffuser Plate for Large LCD-TV” SID‟07 DIGEST, p.50-53 (2007)
71
[12] N. Narendran, Y. Gu, J.P. Freyssinier-Nova, and Y. Zhu, “Extracting Phosphor-Scattered
Photons to Improve White LED Efficiency, “ Phys. Stat. Sol. (A), vol. 202, pp. r60-r62 (2005)
[13]D. Hreniak and W. Sterk, “Synthesis and Optical Properties of Nd3+ doped Y3Al5O12
Nanoceramics,” Journal of Alloys and Compounds, vol. 341, pp.183-186 (2002) [14] H. Luo, J. K. Kim, E. F. Schubert, J. Cho, C. Sone, and Y. Park, “Analysis of
High-Power Packages for Phosphor-Based White-Light-Emitting Diodes,” Appl. Phys.
Lett, vol. 86, 243505 (2005)
[15] S. C. Allen, and A. J. Steckl, “EliXIR-Solid-State Luminaire with Enhanced Light Extraction by Internal Reflection,” Journal of Display Tech., vol. 3(2), pp. 155-159 (2007).
[16] S. C. Allen, and A. J. Steckl, “A Nearly Ideal Phosphor-converted White Light-emitting Diode,” Appl. Phys. Lett. vol. 92, 143309 (2008).
[17] E. Hecht, Optics, 4th Edition, Addison Wesley, p.100 (2002) [18] E. Hecht, Optics, 4th Edition, Addison Wesley, p.98 (2002)
[19] S.O. Kasap, Optoelectronics and Photonics: Principles and Practices, Pearson Prentice Hall, p.18 (2001)
[20] S.O. Kasap, Optoelectronics and Photonics: Principles and Practices, Pearson Prentice Hall, p.18 (2001)
[21] W. J. Smith, Modern Optical Engineering: The Design of Optical Systems, 3rd Edition, Mc-Graw-Hill, p.219 (2000)
[22] N. Ohta and A. R. Robertson, Colorimetry: Fundamentals and Applications, John Wiley
& Sons, p.22 (2005)
[23] E. Veach, Robust Monte Carlo Methods for Light Transport Simulation, Ph.D.
Dissertation, Stanford University, U.S.A. (1998)
72
[24] T. Smith and J. Guild, “The C.I.E. Colorimetric Standards and Their Use,” Transactions
of the Optical Society 33 (3), pp. 73-134 (1931)
[25] R. W. Hunt, Measuring Colour, 3rd Edition, Fountain Press, England, pp. 39-57 (1998) [26] A. C. Harris and I. L. Weatherall, “Objective Evaluation of Colour Variation in the
Sand-burrowing Beetle Chaerodes Trachyscelides White by Instrumental Determination of CIELAB Values,” Journal of the Royal Society of New Zealand, 20(3) (1990)
[27] N. Ohta and A. R. Robertson, Colorimetry: Fundamentals and Applications, John Wiley
& Sons, pp.76 (2005)
[28] N. Ohta and A. R. Robertson, Colorimetry: Fundamentals and Applications, John Wiley
& Sons, pp.115 (2005)
[29] N. Ohta and A. R. Robertson, Colorimetry: Fundamentals and Applications, John Wiley
& Sons, pp.119 (2005)
[30] M. D. Fairchild, Color Appearance Models, Reading, Massachusetts, Addison-Wesley (1998)
[31] D. H. Alman, R. S. Berns, G. D. Snyder, and W. A. Larson, “Performance Testing of Color Difference Metrics Using a Color-Tolerance Dataset,” Color Research and Application, vol. 21, pp.174-188 (1989)
[32] J. Schanda, Colorimetry: Understanding the CIE System, Wiley Interscience, pp. 61-64 (2007)
[33] TCO'06 Media Displays, http://www.tcodevelopment.com/, (2006)
[34]A. Tagaya, M. Nagai, Y. Koike, and K. Yokoyama, “Thin Liquid-Crystal Display Backlight System with Highly Scattering Optical Transmission Polymers,” Applied Optics, vol.40(34), pp.6274-6280 (2001)
[35] H.-T. Huang, C.-C. Tsai, Y.-P. Huang, C.-C. Hsiao, S.-P. Chen, Y.-H. Peng, and W.-C.
Chang, “Dual-Sided Slim LCD Display System with UV Excited Flat Backlight,” SID‟09 DIGEST, pp.1030-1033 (2009)
[36] Y. Ito, T. Tsukahara, S. Masuda, T. Toshida, N. Nada, T. Igarashi, T. Kusunoki, and J.
Ohsako, “Optical Design of Phosphor Sheet Structure in LED Backlight System,” SID‟08
73
DIEST, pp.866-869 (2008)
[37] F.-C. Lin, L.-Y. Liao, C.-Y. Liao, Y.-P. Huang, H.-P. D. Shieh, T.-M. Wang, and S.-C.
Yeh, “Dynamic Backlight Gamma on High Dynamic Range LCD TVs”, Journal of Display Technology, vol. 4(2), pp. 139-152 (2008)
[38] F.-C. Lin, C.-Y. Liao, L.-Y. Liao, Y.-P. Huang, H.-P. D. Shieh, P.-J. Tsai, T.-M. Wang, and Y.-J. Hsieh “Inverse of Mapping Function (IMF) Method for Image Quality
Enhancement of High Dynamic Range LCD TVs,” SID Symposium Digest Tech Papers, vol. 38, pp. 1343-1346 (2007)
[39] C.-Y. Liao, F.-C. Lin, L.-Y. Liao, Y.-P. Huang, and H.-P. D. Shieh, “Inverse of Mapping Function Method for Image Quality Enhancement of Dual-Panel Displays,” IDMC 2007, pp.431-434 (2007)
[40] L.-Y. Liao, F.-C. Lin, Y.-P. Huang, H.-P. D. Shieh, and S.-C. Yeh, “A Real-Time Liquid Crystal Signal Compensation Method for High Dynamic Range LCD,” IDW‟07, pp.
1433-1434 (2007)
[41] G.-Z. Wang, Y.-P. Huang, F.-C. Lin, H.-P. D. Shieh, and S.-C. Yeh, “Delta-Color Adjustment (DCA) Method for Color Controlled Backlight of High Dynamic Range LCD-TVs,” SID‟08 DIGEST, pp. 768-771 (2008)
[42] C.-H. Chen and H.-P. D. Shieh, “Effects of Backlight Profiles on Perceived Image Quality for High Dynamic Range LCDs,” Journal of Display Technology, vol. 4(2), pp.153-159 (2008)