Trends in LCD Backlighting

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Most of today’s LCDs use edge-lit backlighting. Four or more white LEDs are mounted behind one edge of the screen, feeding light into a complex arrangement of light guides, reflectors, and diffusers to ensure even illumination across the whole LCD screen. The LEDs are usually driven by a pulse width modulated signal to adjust the screen brightness to match the ambient light. New technology is becoming available to improve LCD performance.

Pioneered by the LCD TV industry and adopted by Apple on their new iPad is a technology called active backlighting. Active backlighting is a method for enhancing LCD’s contrast and color, making it rival OLED technology’s performance. Active backlighting can raise the contrast ratio of LCD by over ten times to approximately 10,000:1, which matches AMOLED technology. By eliminating the advantage of contrast ratio, OLED becomes less attractive because of its inherent technology issues of burn-in, color shift, and lifetime.

The concept of active backlighting is to mount a large array of multi-color micro LEDs behind the LCD as the backlight and then modulate the LEDs depending on the picture displayed on the screen. By modulating the backlight, you can achieve very black backgrounds and deep colors, increasing the contrast ratio substantially.

With the technical advantages of active backlighting over conventional backlighting, why has it not become mainstream? Several issues have held it back, the cost being the biggest. It can take as many as 300 times the number of LEDs to implement an active backlight system. Other issues are the thickness and the increased complexity of the backlighting control system. Presently, micro-LEDs’ cost and size have decreased, allowing this technology to be implemented into high-end products. Overall it is probably still a couple of years before this technology becomes mainstream and is implemented across multiple market sectors.

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