With the large-scale display of blue and white light-emitting diodes (LEDs) in 1990, whether it is the full-color display using LEDs, or the high attention paid by the public in recent years to energy-saving issues, LED A wide variety of product applications such as smart phones, personal computers (PCs), TV backlights, lighting, white goods, or traffic signs have become more widespread. In order to meet the market demand, the industry has devoted a wide range of product lines, including LEDs for lighting with high color rendering and high reliability, small thin LEDs with PICOLED as products, and customized LEDs for vehicles. Research and development resources.
The output value of white LED for lighting is growing rapidly
Affected by the world's energy-saving trend and the awareness of energy conservation caused by the earthquake in the Tohoku region of Japan, the demand for white LEDs for lighting has increased sharply in the Japanese market, prompting the LED lighting market to continue to grow rapidly. However, to make the lighting source completely from the traditional The conversion of incandescent bulb lighting to LED lighting still has some problems to be solved in terms of product characteristics. Among them, the industry's research and development focus is especially on the high color rendering and high reliability of LED lamps. Share with the technology of luminous efficiency.
Consider both high Ra value and luminous efficiency
The average color rendering index (Ra) is an index of the light source that causes the object to express or reproduce the true color. The higher the index, the better the color reproducibility (the solar light is 100), and the market expects white light for illumination. LEDs have both high luminous efficiency and high color rendering (Ra ≧ 80), but there is a trade-off characteristic between luminous efficiency and Ra (Figure 1). Due to the higher requirements for luminous efficiency in the market, the current market is mostly Ra ≒ 70 high luminous efficiency LED.
Figure 1 shows a trade-off between luminous efficiency and Ra value.
Generally, the package structure of the white LED lamp is to mount the blue LED chip on the substrate and then package the resin containing the phosphor. When the luminescent color (blue) of the LED element is mixed with the luminescent color (yellow, red, green, etc.) of the phosphor, white light is formed.
From the viewpoint of luminous efficiency, white light is generally formed by blue light + yellow light, but this causes poor red light reproducibility and is therefore not suitable for lighting purposes. The general solution adopted is to increase the composition of red light, thereby improving the reproducibility of red light, but this may cause problems in that the luminous efficiency is not ideal.
In order to achieve high luminous efficiency and high Ra value, the company efficiently arranges the phosphor inside the package and solves the problem with the best of both worlds. It has successfully developed Ra≧80 and has high luminous efficiency (Fig. 2). . This series of products has performed very well on the Ra or R9 (red) index. Compared with other brand products with the same Ra value, the series has higher R9 value and better red reproducibility. (image 3). With the breakthrough of this technology, LED lights can not only reduce the chromaticity unevenness, but also respond to more detailed color gradation.
Figure 2 The industry has developed products that combine high luminous efficiency with high Ra values.
Figure 3 The red (R9) value of the new generation of LEDs has increased significantly.
High reliability
In recent years, the demand for reliability in the market has also become increasingly high. In particular, due to the high reflectivity of the LED package, silver plating is generally used, but silver will cause LED beam degradation due to vulcanization (a phenomenon of blackening due to reaction with sulfur), which is caused by outdoor LED lights. Serious problems, so each manufacturer does not propose countermeasures for various silver plating solutions, but this problem cannot be completely improved.
In view of this, the industry has abandoned the silver plating method and changed the nickel plating/gold plating method. After the silver plating of the LED package is changed to nickel plating/gold plating, although the cost is increased and the luminous efficiency is not good due to the decrease of the reflectance, these problems have been successfully overcome after the improvement of the package structure.
The new package structure not only maintains high luminous efficiency, but also achieves high-reliability LED illumination performance. This series of products exhibits excellent performance even in the vulcanization test, and can completely avoid beam degradation.
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