——What are the benefits of using the white LED developed this time?
Shu Ue: It can fully improve the color expression of the LCD panel. This white LED achieves white light by combining green and red phosphor materials on a blue LED chip, so the peaks of the luminescence spectrum are in blue, green, and red. By using a combination of RGB color filters mounted on a liquid crystal panel, images can be displayed in higher purity colors. At present, the mainstream white LED obtains pseudo white through the blue LED chip and the yellow phosphor material, and this white LED significantly improves the color expression of red and green, and the color expression range of the liquid crystal panel can be expanded by 100%. A dozen. It has been applied to some portable terminals and related products have already started to be on the market.
In addition to being used in mobile phones that require beautiful images, many manufacturers consider using backlights with high-color white LEDs as the light source for game consoles. The more the terminal that needs to browse the screen for a long time, the more the user can feel the difference in color.
——High color rendering also has lighting products. What is the difference with a backlight product?
Shu Uemura: The luminescence spectrum is very different. For products such as this backlight, there are significant light intensity troughs between the blue peak and the green peak, and between the green peak and the red peak. In other words, in addition to light that is close to blue, green, and red, try to avoid emitting light of other colors. Because this is more suitable for liquid crystal panels that express color in RGB. The more light that contains RGB, the lower the color purity of the image. This new product also uses a phosphor material that deepens this trough. The new product is characterized by a deep valley of green and red peaks. In addition, in order to make the light emitted by the lighting product closer to natural light, the trough of the luminous intensity should be avoided as much as possible.
Shu Uemura: Indeed, compared to the pseudo-white type, the high color rendering type will reduce the brightness by about 25% even with the same blue LED chip. A pseudo-white product with a brightness of 2.2 to 2.4 cd has been released, and customers have reported that the high-color original product with a brightness of 1.5 cd is "very dark."
However, the brightness of this product has been increased to 1.7cd, no one thinks it is "dark". The reason for this is that although the brightness is lower than that of the pseudo white type product from the numerical value, the brightness can be sufficiently satisfied.
- What improvements have been used to increase the brightness from 1.5 cd to 1.7 cd?
Shu Uemura: A total of three improvements have been made. The color conversion efficiency of the phosphor material, the light extraction efficiency of the package, and the luminous efficiency of the blue LED chip are respectively improved. Among them, the efficiency improvement effect of the phosphor material is most obvious. The specific circumstances are inconvenient to disclose, but they are jointly developed with material manufacturers.
Previously, the green phosphors and red phosphors used in high color rendering products have always had problems of low reliability. Including the wavelength of the light changes with temperature, and the quality deteriorates after damp. There are no such problems with this product.
- Many companies have high color rendering white LEDs. What is the reason why Sharp can take the lead in achieving higher brightness?
Shu Uemura: There should be two reasons. One was developed in conjunction with a phosphor material manufacturer. The phosphor material used in the new product was developed in more than a year. Another reason is that the effect of domestic demand is more obvious. The company has LCD panel business and assembly business, so the LED development team can directly obtain the performance indicators required by the LCD panel backlight source. Therefore, the goal that the high color rendering white LED can achieve can be quickly established.
In addition to the above reasons, it is our advantage to shift the focus of development to high-color white LEDs. High-color products account for nearly half of the company's white LED sales. This ratio may be much higher than other companies. This shows that we attach great importance to high color rendering products.
There is a reason for paying attention to high color rendering white LEDs. From the perspective of LED demand in the future, the prospects for high color rendering products are very good. We expect LED demand in 2008 to reach 520 billion yen, and will expand to 900 billion yen in 2012. It should be emphasized that the market size of products for LCD TV backlights and lighting products will expand. We speculate that these two products will account for 21% and 26% of the market respectively. What these products have in common is "high color rendering." On the other hand, it is expected that the market size of existing LED products will not expand substantially.
——What products are planned to be launched in the future?
Shu Ue: This time, we launched a product with a thickness of 0.6mm. If there is an order, we also hope to continue to introduce other products, including products with a thickness of 0.8mm, to expand the product range of the newly developed high-color products.
Further improvement in brightness will be considered in the future. There is still room for improvement in phosphor materials. The company believes that the material has great potential for development. The package should also be further improved.
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