High Efficiency Uniform LED Surface Light Source

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					High Efficiency Uniform LED Surface
            Light Source
     Chih-Chieh Kang, Jeng-Feng Lin, Yu-Chang Wu, Shih-
                 Cheng Yeh, Tai-Rong Chen
    Department of Electrooptical Engineering, Southern
    Taiwan University, Yung-Kang, Tainan, Taiwan, 71005
                           R.O.C.
                   Abstract
• A novel LED uniform surface light structure is
  devised for the use of lighting, especially for a
  large-size edge-type backlight unit (BLU). Two
  kinds of embodiments are proposed in this
  work. Simulation results demonstrate their
  high efficiency and high uniformity in terms of
  light extraction and illuminance performance,
  respectively.
                  Background
• Going green is the market trend.
• Concept of using “empty cavity” as a light-guiding
  mechanism was proposed more than a decade ago
  for small-size LED backlight unit (BLU) .
• As the size and thickness of a BLU are becoming
  larger and thinner, the optical design of existing
  structures become difficult and complicated.
• Novel design is needed
                          Prior Works
• Y. Nakamura and E. Furuya, “ Liquid
  Crystal Display Device Backlit by
  LED’s Coupled to Printed Circuit
  Board,” US Patent No. 5453855,
  (1995).
• S. Sakai, A. Mori, K. Ishiguchi, K.
  Kobauashi, T. Kokogawa, T.
  Sakamoto, and T. Yoneda, “A Thin
  LED Backlight System with High
  Efficiency for Backlighting 22-in. TFT-
  LCDs,” SID Symposium Digest 37,
  1218-1221, (2004)
• C. P. Hung, W. S. Chen, J. H. Lin, and
  W. Y. Li, “Novel Design for LED Lens
  and Backlight System,” Proceedings
  of IDMC 2007, Taiwan, 476-479,
  (2007)
         Optical Design Principle
• Bullet-shape LEDs with high-directivity intensity
  profile.
• One central bump and several pairs of side slant
  structures on the bottom reflection surface for
  illuminace uniformity by light modulation.
• Improve illumiance uniformity by a diffusion plate.
• Reverse prism layer structure to greatly enhance
  luminance performance.
           Optical Designs




                 (a) only a diffusion plate




(b) a diffusion plate with a reverse prism layer structure
          High-Directivity LED
• For exampe




   Nichia NSPW500B   Radiation pattern
   Bottom Reflection Surface with
         Bumpy Structures
• Illuminace uniformity improvement
• Enhancement of light extraction efficiency




             BLU implemented is of 62.6 × 234× 15.9 mm
            Optical Simulation (a)
• only a diffusion plate ontop of the “empty cavity”
  No diffusion plate presents
   Light extraction efficiency = 91%
            Optical simulation (a)
• only a diffusion plate ontop of the “empty cavity”
  Diffusion plate presents
  Light extraction efficiency = 77%
  Illuminance uniformity = 72%
    Reverse Prism Layer Structure
• Redirect the light rays toward the direction of
  normal viewing angle
• Enhancement of light extraction efficiency
Refocusing Effect of Reverse Prism
         Layer Structure
                          Light rays emitting
                          from LEDs on the
                          left side modulated
                          by the left side slant
                          structure




                          Light rays emitting
                          from LEDs on the
                          right side
                          modulated by the
                          central bump
            Optical Simulation (b)
• A reverse prism layer structure ontop of the “empty cavity”
  No diffusion plate presents

  Light extraction efficiency = 94%
             Optical simulation (b)
• A diffusion plate with a reverse prism layer structure
  ontop of the “empty cavity”
  Light extraction efficiency = 89%
  Illuminance uniformity = 60%
                   Conclusion
• We can highly increase the light extraction efficiency
  up to be 90% that is comparable to some direct-type
  LED BLUs .
• Our second devised embodiment can greatly
  increase the luminance performance by the
  implementation of the reverse prism layer structure
  as well as the manipulation the transmittance of a
  diffusion plate.
• More work is needed on optimizing optical design in
  order to improve the uniformity on both illuminance
  and luminance.

				
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posted:11/12/2011
language:English
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