With the blue and white light-emitting diodes (LEDs) moving towards practicality in 1990, LEDs are not only used for full-color displays, but also in recent years, the public has attached great importance to energy-saving issues. The diversified product application areas such as smartphones, personal computers (PCs), TV backlights, lighting, white goods, or traffic signs are becoming more and more widespread. In order to meet market demands, the industry has devoted considerable attention to various product series, including lighting LEDs that can achieve high color rendering and high reliability, small and thin LEDs represented by PICOLED products, and customized color LEDs for vehicles. R & D resources.
The output value of white LED for lighting is growing rapidly
Affected by the world's energy conservation trends and the rising awareness of energy conservation caused by the Great East Japan Earthquake, the demand for white LEDs for lighting in the Japanese market has increased significantly, prompting the LED lighting market output value to continue to grow rapidly. The conversion of incandescent bulb lighting to LED lighting still has some problems that need to be solved in terms of product characteristics. Among them, the industry's research and development focuses on the high color rendering and high reliability of LED lamps. The following will be employed for high Ra values Share with luminous efficiency technology.
Both high Ra value and luminous efficiency
The average color rendering index (Ra) is an index that the light source causes the object to express or reproduce the true color. The higher the index, the better the color reproducibility (Ra of sunlight is 100). The market expects white light for lighting LED can have both high luminous efficiency and high color rendering (Ra ≧ 80), but there is a trade-off characteristic between luminous efficiency and Ra value (Figure 1). Since the market has higher requirements for luminous efficiency, the current market is mostly Ra ≒ 70 high luminous efficiency LEDs.
Figure 1 There is a trade-off between luminous efficiency and Ra value.
The packaging structure of a general white LED lamp is to mount a blue LED chip on a substrate, and then encapsulate it with a resin containing phosphor. When the luminous color of the LED element (blue) and the luminescent color of the phosphor (yellow, red, green, etc.) are mixed, white light is formed.
From the point of view of luminous efficiency, blue light + yellow light are generally used to form white light, but this will cause poor reproducibility of red light, so it is not suitable for lighting applications. The solution generally adopted is to increase the composition of red light, thereby improving the reproducibility of red light, but this will cause the problem of undesirable luminous efficiency.
In order to take into account both high luminous efficiency and high Ra value, the industry has effectively placed the phosphor inside the package, using the best of both worlds as a solution, and successfully developed a product with Ra ≥ 80 and extremely high luminous efficiency (Figure 2) . The performance of this series of products on the Ra or R9 (red) index is very good. Compared with other brands of the same Ra value, this series of products has a higher R9 value and better red reproducibility. (image 3). With the breakthrough of this technology, LED lights can not only reduce the unevenness of chromaticity, but also respond to more detailed chromaticity levels.
Figure 2 The industry has developed products that take into account both high luminous efficiency and high Ra value.
Figure 3 The performance of the red (R9) value of the new generation LED has been greatly improved.
High reliability
In recent years, the demand for reliability in the market has become increasingly high. Especially due to the high reflectivity of LED packages, 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. There is a serious problem, so various manufacturers have to put forward various countermeasures for silver plating solutions, but at present this problem cannot be completely improved.
In view of this, the industry abandoned the silver plating method and adopted the nickel / gold plating method. After changing the silver plating of the LED package to nickel plating / gold plating, although it will lead to increased costs and poor luminous efficiency due to the decrease in reflectivity, these problems have been successfully overcome after the improvement of the packaging structure.
The new package structure not only maintains high luminous efficiency, but also achieves high-reliability LED luminous performance. This series of products has shown excellent performance even in the vulcanization test, which can completely avoid the phenomenon of beam degradation.
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