In recent years, LED lighting has made breakthroughs, its luminous efficiency has been continuously improved, and product prices have become lower and lower. With the vigorous promotion of the government, it is rapidly replacing traditional lighting products, and its market share is increasing day by day. Although LED applications continue to advance, the limit of its luminous efficiency has always been an international question, and packaging technology, which is closely related to light color, plays a very important role.
The solid-state lighting team of Taiwan's National Central University assembled several domestic and foreign experts who specialize in photoelectric and thermal colors. After three years of research, this year they presented an important research result, which was to explore the limits of white LED packaging efficiency. This paper was published in the "Journal of Solid State Lighting" in November. In just three weeks, it became the original paper with the highest click rate in a single month. It was also the representative paper of the journal in its first year of publication, and it has won two academic paper awards in a short period of time.
Sun Qingcheng, leader of the research team and director of the Optoelectronics Center of Central University, said that this research is closely related to the phosphor formula, packaging geometry and blue light chip of white LEDs. The complexity of system integration is extremely high, so there are not many teams in the world that can conduct in-depth research. In order to accurately grasp the limits of packaging efficiency, the research team conducted accurate and systematic simulations and analyzes using the internationally leading phosphor optical model developed over many years. At the same time, it conducted experiments to measure and compare six main packaging structures. It was found that the effective combination of packaging structure and phosphor formula is an important factor in improving packaging efficiency.
The research team found that under ordinary yellow phosphors, the packaging efficiency after optimizing the combination of phosphors and packaging structures can theoretically reach a limit of more than 75%. Compared with white LED products on the market, the packaging efficiency generally falls below 55%. It is obvious that there is still huge room for improvement. The research team adjusted the phosphor formula and packaging geometry based on the simulation results without affecting the color performance. After actual experimental measurements, they achieved a packaging efficiency of close to 70%, which is quite close to the theoretical limit and is a leading indicator in the published literature.
Yang Zongxun, a professor in the Department of Optoelectronics who is responsible for color performance, said that in addition to revealing the module limits of packaging efficiency, this study also further deduced the system luminous efficiency limits of white LEDs. The important thing is that LED luminous efficiency is closely related to color performance. There are some exaggerated luminous efficiency reports in the world, some of which are based on the premise of sacrificing color performance and will not be practical for general lighting. At the same time, although the luminous efficiency of white LEDs with better color performance may be slightly lower, they are worthy of technology investment because of their wider application range.
Zhong Deyuan, a professor in the Department of Optoelectronics who is responsible for thermal research, further stated that the research team also found that phosphors have unique temperature distribution and are actively obtaining accurate temperature field experimental data, which will help optimize the heat dissipation design of high-power white LED packaging structures.
Sun Qingcheng said that based on the above-mentioned research results, the research team has developed a new packaging structure that has the possibility to practice the theoretical limit of packaging efficiency. It can also demonstrate higher packaging efficiency and achieve better energy-saving effects when packaging dual phosphors with high power and high color rendering properties. This new technology, which has been patented by Taiwan and the United States, currently has two listed companies engaged in technology transfer cooperation, and another internationally renowned company is negotiating to directly apply it in its existing best-selling optoelectronic products. Students participating in the research have also been recruited by relevant domestic manufacturers with high salaries, and have excellent performance in industry and academia.
ANNA