Ultra-slim Direct-lit LCD Backlight Using Glass Light Guide Plate
◆We report on the design and performance of a direct-lit LCD backlight prototype which is only 5 nun thick and capable of full array 2D local dimming. Equipped with a 15.6” LC display panel, the prototype reaches peak brightness of 2000 nits. The measured contrast numbers meet VESA Display HDR 600 specification.
◆To remain competitive with OLED and other emerging display technologies, liquid crystal displays (LCD) follow general trends of increasing resolution, higher peak brightness and dynamic range (HDR). higher contrast, thinner set design, and narrower bezels. The demands of increased peak brightness and contrast can currently only be met using so-called direct-lit backlights, with a 2D array of light sources directly behind the LCD panel. As was shown in the pioneering work by H. Seetzen and co-authors [1], so-called local dimming, or selective addressing of the individual light sources in the array, allows reaching ANSI (checkerboard pattern) contrast approaching 300000:1, even with 2004 technology. Since then, the performance of light sources, algorithms used for local dimming [2], and the native contrast of the LCD panels were steadily improving.
◆One challenge that remains difficult for the direct-lit backlights to address is reducing the thickness. The sources in modem designs are typically either blue or white light emitting diodes (LED), capable of generating significant light power from a relatively small package. To make the backlight brightness uniform, so-called optical diffuser plates (DP), sometimes in a combmation with lenses modifying (widening) angular distribution of the LED output (so-called 2nd lenses), are placed over the LED array at a distance known as “optical distance” (OD). However, even when using 2nd lenses, it is very difficult to achieve OD < about 1/4 of the LED pitch P (distance between LED centers in the 2D array). In current high-end commercial TV sets, the pitch P is typically in the range 30-40 mm and OD is 9-10 nun. which is achieved by using a thick (1.5-3 nun) and dense optical diffuser.
◆We have previously reported on a thin backlight design where side-emitting LED sources are inserted into holes in the glass light guide plate (LGP) [3]. Essentially, the design preserves the thin form factor of the edge-lit backlight while enabling 2D dimming capability. Promising performance was demonstrated, but prospects of this design are limited by the lack of commercially available side-emitting LED devices.
◆In this work, we describe a backlight unit (BLU) design with the LED pitch P of 43 nun and the effective OD of 1.35 mm. less than 1/30 of the LED pitch. The design is using a glass LGP optically bonded to the LED sources. The total backlight thickness, including the printed circuit board (PCB), is ~ 5 mm. The prototype LCD display constructed to evaluate the performance of the backlight is less than 8 mm thick.
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Technical Documentation |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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August 2021 |
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4.7 MB |
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