Abstract

We propose an optical design process that significantly reduces the time and costs in direct backlight unit (BLU) development. In it, the basic system specifications are derived from the optical characteristics of RGB light-emitting diodes (LEDs) comprising the BLU. The driving currents are estimated to determine the theoretical RGB flux ratio for a desired white point. The number of LEDs needed to produce the target luminance is then calculated from the combined optical efficiencies of the components. Last, an appropriate array configuration is sought based on the illuminance distribution function for meeting the target uniformity. To showcase the design process we built two 42-inch triangular cluster arrays of 40 × 16 LED elements. When a flat reflective sheet was used, the minimum thickness required of the system to satisfy the target uniformity was 30 mm. Introducing a patterned reflective sheet removed hotspots that resulted from reducing the system thickness without the aid of additional optical components. Using an optimized patterned reflective sheet, reduction in system thickness as much as 5 mm was possible.

© 2010 OSA

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References

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  1. D. M. Brown, R. Dean, and J. D. Brown, “LED backlight: design, fabrication, and testing,” Proc. SPIE 3938, 180–187 (2000).
    [CrossRef]
  2. E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
    [CrossRef] [PubMed]
  3. M. Anandan, “Progress of LED backlights for LCDs,” J. Soc. Inf. Disp. 16(2), 287–310 (2008).
    [CrossRef]
  4. G. Wyszecki and W. S. Stiles, Color Science 2nd Edition (Wiley, New York, 1982).
  5. K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
    [CrossRef]
  6. S. Muthu and J. Gaines, “Red, green and blue LED-based white light source: Implementation challenges and control design,” in Proc. IEEE IAS Annu. Meeting 1 515–522 (2003).
  7. P. Deurenberg, C. Hoelen, J. van Meurs, and J. Ansems, “Achieving color point stability in RGB multi-chip LED modules using various color control loops,” Proc. SPIE 5941, 59410C (2005).
    [CrossRef]
  8. Ki-Chan Lee, Seung-Hwan Moon, Brian Berkeley, and Sang-Soo Kim,“Optical feedback system with integrated color sensor on LCD,” Sens, Actuators A 130–131, 214–219 (2006).
  9. W. Robert, Boyd, Radiometry and Dectection of Optical Radiation (Wiley, New York, 1983).
  10. G. Harbers, S. J. Bierhuizen, and M. R. Krames, “Performance of high power light emitting diodes in display illumination applications,” J. Display Technol. 3(2), 98–109 (2007).
    [CrossRef]
  11. I. Moreno, M. Avendaño-Alejo, and R. I. Tzonchev, “Designing light-emitting diode arrays for uniform near-field irradiance,” Appl. Opt. 45(10), 2265–2272 (2006).
    [CrossRef] [PubMed]
  12. P. C.-P. Chao, L.-D. Liao, and C.-W. Chiu, “Design of a Novel LED Lens Cap and Optimization of LED Placement in a Large Area Direct Backlight for LCD-TVs,” Proc. SPIE 6196, 61960N (2006).
    [CrossRef]
  13. Yankun Zhen, Zhenan Jiaa, and Wenzi Zhang, “The Optimization of Directly-Under-Light Type Backlight Module Structure for Brightness Uniformity,” Key Engineering Materials 364 – 366, 166–171 (2008).
  14. B. Kim, M. Choi, H. Kim, J. Lim, and S. Kang, “Elimination of flux loss by optimizing the groove angle in modified Fresnel lens to increase illuminance uniformity, color uniformity and flux efficiency in LED illumination,” Opt. Express 17(20), 17916–17927 (2009).
    [CrossRef] [PubMed]

2009

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

B. Kim, M. Choi, H. Kim, J. Lim, and S. Kang, “Elimination of flux loss by optimizing the groove angle in modified Fresnel lens to increase illuminance uniformity, color uniformity and flux efficiency in LED illumination,” Opt. Express 17(20), 17916–17927 (2009).
[CrossRef] [PubMed]

2008

M. Anandan, “Progress of LED backlights for LCDs,” J. Soc. Inf. Disp. 16(2), 287–310 (2008).
[CrossRef]

Yankun Zhen, Zhenan Jiaa, and Wenzi Zhang, “The Optimization of Directly-Under-Light Type Backlight Module Structure for Brightness Uniformity,” Key Engineering Materials 364 – 366, 166–171 (2008).

2007

2006

I. Moreno, M. Avendaño-Alejo, and R. I. Tzonchev, “Designing light-emitting diode arrays for uniform near-field irradiance,” Appl. Opt. 45(10), 2265–2272 (2006).
[CrossRef] [PubMed]

Ki-Chan Lee, Seung-Hwan Moon, Brian Berkeley, and Sang-Soo Kim,“Optical feedback system with integrated color sensor on LCD,” Sens, Actuators A 130–131, 214–219 (2006).

P. C.-P. Chao, L.-D. Liao, and C.-W. Chiu, “Design of a Novel LED Lens Cap and Optimization of LED Placement in a Large Area Direct Backlight for LCD-TVs,” Proc. SPIE 6196, 61960N (2006).
[CrossRef]

2005

P. Deurenberg, C. Hoelen, J. van Meurs, and J. Ansems, “Achieving color point stability in RGB multi-chip LED modules using various color control loops,” Proc. SPIE 5941, 59410C (2005).
[CrossRef]

E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
[CrossRef] [PubMed]

2000

D. M. Brown, R. Dean, and J. D. Brown, “LED backlight: design, fabrication, and testing,” Proc. SPIE 3938, 180–187 (2000).
[CrossRef]

Anandan, M.

M. Anandan, “Progress of LED backlights for LCDs,” J. Soc. Inf. Disp. 16(2), 287–310 (2008).
[CrossRef]

Ansems, J.

P. Deurenberg, C. Hoelen, J. van Meurs, and J. Ansems, “Achieving color point stability in RGB multi-chip LED modules using various color control loops,” Proc. SPIE 5941, 59410C (2005).
[CrossRef]

Avendaño-Alejo, M.

Berkeley, Brian

Ki-Chan Lee, Seung-Hwan Moon, Brian Berkeley, and Sang-Soo Kim,“Optical feedback system with integrated color sensor on LCD,” Sens, Actuators A 130–131, 214–219 (2006).

Bierhuizen, S. J.

Brown, D. M.

D. M. Brown, R. Dean, and J. D. Brown, “LED backlight: design, fabrication, and testing,” Proc. SPIE 3938, 180–187 (2000).
[CrossRef]

Brown, J. D.

D. M. Brown, R. Dean, and J. D. Brown, “LED backlight: design, fabrication, and testing,” Proc. SPIE 3938, 180–187 (2000).
[CrossRef]

Chao, P. C.-P.

P. C.-P. Chao, L.-D. Liao, and C.-W. Chiu, “Design of a Novel LED Lens Cap and Optimization of LED Placement in a Large Area Direct Backlight for LCD-TVs,” Proc. SPIE 6196, 61960N (2006).
[CrossRef]

Chiu, C.-W.

P. C.-P. Chao, L.-D. Liao, and C.-W. Chiu, “Design of a Novel LED Lens Cap and Optimization of LED Placement in a Large Area Direct Backlight for LCD-TVs,” Proc. SPIE 6196, 61960N (2006).
[CrossRef]

Choi, M.

Dean, R.

D. M. Brown, R. Dean, and J. D. Brown, “LED backlight: design, fabrication, and testing,” Proc. SPIE 3938, 180–187 (2000).
[CrossRef]

Deurenberg, P.

P. Deurenberg, C. Hoelen, J. van Meurs, and J. Ansems, “Achieving color point stability in RGB multi-chip LED modules using various color control loops,” Proc. SPIE 5941, 59410C (2005).
[CrossRef]

Han, D. J.

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

Harbers, G.

Hoelen, C.

P. Deurenberg, C. Hoelen, J. van Meurs, and J. Ansems, “Achieving color point stability in RGB multi-chip LED modules using various color control loops,” Proc. SPIE 5941, 59410C (2005).
[CrossRef]

Jiaa, Zhenan

Yankun Zhen, Zhenan Jiaa, and Wenzi Zhang, “The Optimization of Directly-Under-Light Type Backlight Module Structure for Brightness Uniformity,” Key Engineering Materials 364 – 366, 166–171 (2008).

Kang, S.

Kim, B.

Kim, H.

Kim, J. K.

E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
[CrossRef] [PubMed]

Kim, Sang-Soo

Ki-Chan Lee, Seung-Hwan Moon, Brian Berkeley, and Sang-Soo Kim,“Optical feedback system with integrated color sensor on LCD,” Sens, Actuators A 130–131, 214–219 (2006).

Krames, M. R.

Lee, Ki-Chan

Ki-Chan Lee, Seung-Hwan Moon, Brian Berkeley, and Sang-Soo Kim,“Optical feedback system with integrated color sensor on LCD,” Sens, Actuators A 130–131, 214–219 (2006).

Li, W.

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

Liang, K.

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

Liao, L.-D.

P. C.-P. Chao, L.-D. Liao, and C.-W. Chiu, “Design of a Novel LED Lens Cap and Optimization of LED Placement in a Large Area Direct Backlight for LCD-TVs,” Proc. SPIE 6196, 61960N (2006).
[CrossRef]

Lim, J.

Liu, X. L.

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

Moon, Seung-Hwan

Ki-Chan Lee, Seung-Hwan Moon, Brian Berkeley, and Sang-Soo Kim,“Optical feedback system with integrated color sensor on LCD,” Sens, Actuators A 130–131, 214–219 (2006).

Moreno, I.

Ren, H. R.

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

Schubert, E. F.

E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
[CrossRef] [PubMed]

Tzonchev, R. I.

van Meurs, J.

P. Deurenberg, C. Hoelen, J. van Meurs, and J. Ansems, “Achieving color point stability in RGB multi-chip LED modules using various color control loops,” Proc. SPIE 5941, 59410C (2005).
[CrossRef]

Wang, W. J.

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

Yang, R.

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

Zhang, Wenzi

Yankun Zhen, Zhenan Jiaa, and Wenzi Zhang, “The Optimization of Directly-Under-Light Type Backlight Module Structure for Brightness Uniformity,” Key Engineering Materials 364 – 366, 166–171 (2008).

Zhen, Yankun

Yankun Zhen, Zhenan Jiaa, and Wenzi Zhang, “The Optimization of Directly-Under-Light Type Backlight Module Structure for Brightness Uniformity,” Key Engineering Materials 364 – 366, 166–171 (2008).

Appl. Opt.

Displays

K. Liang, W. Li, H. R. Ren, X. L. Liu, W. J. Wang, R. Yang, and D. J. Han, “Color measurement for RGB white LEDs in solid-state lighting using a BDJ photodetector,” Displays 30(3), 107–113 (2009).
[CrossRef]

J. Display Technol.

J. Soc. Inf. Disp.

M. Anandan, “Progress of LED backlights for LCDs,” J. Soc. Inf. Disp. 16(2), 287–310 (2008).
[CrossRef]

Key Engineering Materials

Yankun Zhen, Zhenan Jiaa, and Wenzi Zhang, “The Optimization of Directly-Under-Light Type Backlight Module Structure for Brightness Uniformity,” Key Engineering Materials 364 – 366, 166–171 (2008).

Opt. Express

Proc. SPIE

P. C.-P. Chao, L.-D. Liao, and C.-W. Chiu, “Design of a Novel LED Lens Cap and Optimization of LED Placement in a Large Area Direct Backlight for LCD-TVs,” Proc. SPIE 6196, 61960N (2006).
[CrossRef]

D. M. Brown, R. Dean, and J. D. Brown, “LED backlight: design, fabrication, and testing,” Proc. SPIE 3938, 180–187 (2000).
[CrossRef]

P. Deurenberg, C. Hoelen, J. van Meurs, and J. Ansems, “Achieving color point stability in RGB multi-chip LED modules using various color control loops,” Proc. SPIE 5941, 59410C (2005).
[CrossRef]

Science

E. F. Schubert and J. K. Kim, “Solid-state light sources getting smart,” Science 308(5726), 1274–1278 (2005).
[CrossRef] [PubMed]

Sens, Actuators A

Ki-Chan Lee, Seung-Hwan Moon, Brian Berkeley, and Sang-Soo Kim,“Optical feedback system with integrated color sensor on LCD,” Sens, Actuators A 130–131, 214–219 (2006).

Other

W. Robert, Boyd, Radiometry and Dectection of Optical Radiation (Wiley, New York, 1983).

S. Muthu and J. Gaines, “Red, green and blue LED-based white light source: Implementation challenges and control design,” in Proc. IEEE IAS Annu. Meeting 1 515–522 (2003).

G. Wyszecki and W. S. Stiles, Color Science 2nd Edition (Wiley, New York, 1982).

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Figures (10)

Fig. 1
Fig. 1

Optical design process for a direct BLU system using a multi-chip LED array.

Fig. 2
Fig. 2

Optical design process of multi-chip LED by (a) Measured output fluxes of RGB chip with an LED measurement system and compensation of the driving currents, (b) verification of optical properties by input fluxes of 2.52 lm (PR), 9.85 lm (PG) and 0.55 lm (PB) applied to ray-tracing simulation, (c) verification of optical properties by input currents of 25.8 mA (IR), 23 mA (PG) and 31.7 mA (PB) applied to experimental unit LED.

Fig. 3
Fig. 3

Comparison of the area of overlap among LEDs in (a) rectangular and (b) triangular clusters with the same row and column spacing.

Fig. 4
Fig. 4

Configuration of BLU System with (a) Triangular cluster of 640 LEDs consisting of 64 units of 10 LEDs for local dimming and (b) the ideal illuminance distribution at 30 mm, the minimum distance having optimal uniformity as calculated from Eq. (3).

Fig. 5
Fig. 5

Illuminance distribution at z = 20 mm (a) by Eq. (3) and (b) by ray-tracing simulation. Analysis of the variation between the two illuminance patterns in the (c) x-axis direction (y = 0) and (d) y-axis direction (x = 0) to verify the simulation accuracy of the BLU system models.

Fig. 6
Fig. 6

(a) Schematic of the reflection characteristics for uniform illuminance redistribution using a patterned reflective sheet structure, (b) sheet structure modeling for the ray-tracing simulation and the 7 illuminance points in the unit triangular cluster used to calculate the average illuminance deviation for the uniformity evaluation.

Fig. 7
Fig. 7

Distribution graph of the average deviation calculated from ray-tracing simulation to find the optimum shape for the patterned reflective sheet within the variable ranges (a) at z = 20mm and (b) at z = 25mm.

Fig. 8
Fig. 8

The variation in the average deviation between a flat reflective sheet (points A0 and B0 in Fig. 7) and a patterned reflective sheet with a minimum average deviation value (points A1 and B1 in Fig. 7) depending on the thickness. The average deviation value for the optimal patterned reflector 25 mm thick was 0.00633, which was less than the hotspot criterion value of 0.00767.

Fig. 9
Fig. 9

Ray-tracing simulations for the illuminance distribution for the entire BLU system with an average deviation value of (a) 0.0367 using a flat reflective sheet (condition A0: h = 0 mm, w = 0 mm) at z = 20 mm, (b) 0.016 by using an optimal patterned triangular reflective sheet (condition A1: h = 7 mm, w = 12 mm) at z = 20 mm, (c) 0.0137 using a flat reflective sheet (condition B0: h = 0 mm, w = 0 mm) at z = 25 mm, and (d) 0.00633 using an optimal patterned triangular reflective sheet (condition B1: h = 5 mm, w = 11 mm) at z = 25 mm.

Fig. 10
Fig. 10

The measured illuminance distribution images on diffuser plate of 25-mm-thick BLU system with (a) an average deviation of 0.0148, using a flat reflective sheet (condition B0: h = 0 mm, w = 0 mm) and (b) an average deviation of 0.0073, using an optimal patterned triangular reflective sheet (condition B1: h = 5 mm, w = 11 mm) in mold frame of aspect ratio 16:9 with 640 multi-chip LEDs.

Tables (1)

Tables Icon

Table 1 M × N array configurations of 640 LEDs for a 42-inch BLU and the radius of the overlapping area

Equations (4)

Equations on this page are rendered with MathJax. Learn more.

[ L R I R L G I G L B I B ] = [ P R P G P B ] = 1 y w [ y R       0       0 0       y G       0 0       0       y B ] × [ x R       x G       x B y R       y G       y B z R       z G       z B ] 1 × [ x w y w z w ] ,
    n         π A B L U L B L U T L C D η B L U Φ L E D ,
E ( x , y , z )     =     z 3 j = 1 M i = 1 N { [ x a ( M + 1 2 j ) 2 ] 2 + [ y b ( N + 2 i ) 2 ] 2 + z 2 } 3 2 ,
E d e v i a t i o n = 1 E a v g k = 1 n ( E k E a v g ) 2 n ,

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