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Optoelectronics/Displays??

Utilising LEDs for LCD backlighting (Part 2)

Posted: 13 Feb 2015 ?? ?Print Version ?Bookmark and Share

Keywords:LED? LCD backlight? TFT-LCDs? CRT? backlight unit?

In Part 1, we described the types and structures of LED LCD backlight units and their relative advantages. That first installment concluded with a summary of market requirements for BLUs and a history of how they've driven their development. This second and final installment begins with a close look at recent market trends and technological development and concludes with the key points in the optical design of LED backlights.

Market trends
Over the past decade, LEDs have slowly been incorporated into various LCD devices, initially in mobile phones and recently in LCD televisions. Due to a combination of factors, including the fact that OLED development has made less progress than expected, that there has been no significant breakthrough in the technology of other light sources used in LCDs and that the quality of LEDs has been continuously improved, LCDs with an LED BLU have gradually become the best choice for displays. For LCD devices, the quality and features of the light source affect or even directly determine the optical quality and market competitiveness of the LCD products. Several advantages of LEDs solve a few of the outstanding problems with LCDs. It is clear that using an LED inside an LCD has increased the mainstream status of LCDs. A market forecast for large BLUs based on a survey by LED inside published in August 2011 is shown in figure 4.

Figure 4: Market forecast for large BLUs based on a survey by LEDinside published in August 2011.

A cost forecast based on a survey produced by NPD DisplaySearch for different BLU types for 32-inch high-definition (HD) 60Hz LCD televisions is shown in figure 5.4

Figure 5: Cost forecast for different BLU types for 32-inch HD 60Hz LCD televisions.4

The high cost of LED BLUs obviously affects the commercial market penetration of LCDs based on LEDs. To reduce costs, television manufacturers have been adopting two-chip LEDs to reduce the number of LEDs. The number of LEDs used per set with a direct- type BLU is expected to be less than in a set with an edge- type BLU.4 Figure 6 shows a forecast for the number of LED packages per television set.17

Figure 6: Forecast for number of LED packages per television set.17


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