A comparison of image quality between Toshiba's previous LCD TV (right) and its new product (left), which combines a white LED backlight and local dimming. The LED-backlit model on the left uses a glossy panel.
A comparison of image quality between Toshiba's previous LCD TV (right) and its new product (left), which combines a white LED backlight and local dimming. The LED-backlit model on the left uses a glossy panel.
[Click to enlarge image]

"White LEDs, not RGB three-color LEDs, will be the mainstream LED backlight for LCD TVs," said Yuji Motomura, Marketing Group, TV Division, Digital Media Network Company of Toshiba Corp.

Motomura attended a presentation of new products in Toshiba's "Regza" series of LCD TVs April 7, 2009, and answered a question on LED backlights as noted above (See related article).

TV manufacturers have announced their new LCD TV products with image quality enhanced by LED backlights in succession since the end of August 2008. Sony announced LCD TVs whose dynamic contrast was improved to 1,000,000:1 by combining an LED backlight and local dimming technology Aug 28, 2008 (See related article 2).

Sharp Corp followed Sony by introducing a LCD TV with a dynamic contrast boosted to 1,000,000:1 by combining an LED backlight and local dimming technology Sept 30, 2008.

"Highest image quality" despite white LED backlight

The major difference of Toshiba's LED backlight from Sony's and Sharp's backlights is its method used for the LED light source. While both Sony and Sharp used RGB three-color LED light sources, Toshiba employed white LED light source.

Generally speaking, RGB LEDs, rather than white LEDs, broaden "color gamut," one of the major indices of image quality. Nevertheless, Toshiba used white LEDs for its new LCD TVs, which it claims are "the highest image quality models of Regza products."

When asked why, Motomura said, "In fact, image quality is higher with a white LED backlight."

He explained it as follows. First, white LED light sources are more efficient in boosting image quality because the white balance fluctuates more easily when the light source is RGB LEDs. Second, image quality becomes more likely to degrade if the color gamut is extended more than necessary because it causes the display to render incorrect colors.

It is true that RGB LED backlights offer a wider color gamut than white LED backlights, but the color reproduction range of white LEDs is sufficient to render colors of most objects, Motomura said.

Cost lower than RGB LED-backlit TVs

In addition, white LED backlights make it easier to simplify backlight control systems because they only require a system to control white color, instead of the three RGB colors. In respect not only to the LED light source itself but also to the control system, white LEDs can be regarded as superior in terms of manufacturing costs, Motomura said.

"There is one more reason other than those concerning image quality," he said. "I think you will understand why we employed white LEDs and why we expect white LEDs to become a new trend, if you look at the street pricing expected for our new products."

The estimated market prices for the aforementioned Sony's 55- and 46-inch LCD TVs were approximately ¥750,000 (approx US$7,541) and 600,000, respectively (when they were released). And those for Sharp's 65- and 52-inch LCD TVs were ¥1.28 million and 980,000, respectively. On the other hand, Toshiba's 55- and 46-inch products are expected to be priced at about ¥600,000 and 500,000, respectively.