Dr. Sun Decai, Senior Product Development Manager at Philips Lumileds, was interviewed during the LED Forward Technology Seminar at OFweek Semiconductor Lighting Network. In the interview, Dr. Sun Decai answered questions about the extent to which white LEDs will develop in the future and how to solve the heat dissipation problem.
Thin film fluorescent plate technology enhances LED light quality
Dr. Sun Decai introduced the technology of thin film fluorescent panel. One advantage of Philips Lumileds is that the film flip chip technology has now developed into the second generation flip chip technology. By conducting the gold ball under the chip, the surface of the chip is completely flat, so Philips Lumileds products can use fluorescent plate technology, which is to put the phosphor on a solid film, and then put the fluorescent plate on the chip. The advantage of this is that the chromatic aberration caused by the uneven coating of the conventional phosphor can be avoided, and the light extraction rate is about 10% higher than that of the conventional smeared phosphor. This technology greatly improves the light quality of the LED and can also reduce it. Cost of production.
Philips Lumileds is the first in the industry to release the LM 80 report, and it is fully open to download on the official website without signing a confidentiality agreement. This reflects Philips Lumileds' confidence in reporting data because it is based on the results of a large amount of test data, accumulating 700 million The test, 15,000 hours of test data, so we are very confident to disclose the data.
After 3 years, the warm white LED light effect can be 150LM/W. The price reduction is still very large.
When talking about the extent to which white LEDs will develop in the future, Dr. Sun Decai returned to the road. Now the indoor lighting people feel the most comfortable warm white LED light effect is about 100LM/W, and will reach 150lm/w warm white light after 3 years. According to the prediction of the US Department of Energy, the overall level of warm white light and color temperature 3000k LED light efficiency industry will reach 120LM/W in 2012, and cold white temperature 5000-6000k can reach 180-200LM/W. LEDs can meet most of the needs of 150-160LM/W. 150LM/W LED, plus 30% reduction of the overall efficiency of the luminaire system, there is also a comprehensive light effect of 100LM/W, while cold white LED will reach 200LM/W in 3 years, then the application of cold white light products such as LED street lamps The luminous efficiency can reach 150LM/W, which is much better than the traditional light source. In this case, the LED is mainly facing cost problems. At that time, there will be less research on the improvement of light efficiency, and the steps of improvement will be slowed down. The main direction of research is to reduce the cost of products.
Dr. Sun Decai, Senior Product Development Manager, Philips Lumileds
Dr. Sun Decai also stressed that the above mentioned Philips Lumileds LED product efficacy refers to the light effect in actual use. In the luminaire, the LED junction temperature has reached 65 ° C to 80 ° C or even 100 ° C. At this temperature, the general white LED light efficiency will be reduced by about 10-20%, while the Philips Lumileds LED product efficacy From 25 ° C to 85 ° C almost unchanged, the actual luminous efficiency is very high, the LED light effect under actual working conditions is the customer's most concerned.
Now the LED production problem is mainly that the LED yield is much lower than 90% of the integrated circuit. The LED yield is generally 30%-70%, and there will be more progress in the next three years.
In terms of integrated light efficiency and yield, LEDs still have a lot of room for price cuts. The US Department of Energy predicts that prices will drop to 1000 LM/dollar in five years.
In addition, Dr. Sun Decai mentioned that the color temperature distribution of white light and the control of color temperature are also difficult problems. Philips Lumileds has done a good job in this respect and can already achieve the degree that the human eye can't distinguish.
Heat problem persists for a long time
Regarding the issue of heat dissipation, Dr. Sun Decai believes that this is a long-term problem facing the industry. At present, 80% of the energy conversion of LEDs is converted into heat, and the luminous efficiency is more than doubled and 50% of the energy is converted into heat. Blu-ray LEDs Philips Lumileds achieves 60% overall efficiency, ie 60% of energy is converted to light and 40% is heat. White LEDs are less efficient than phosphors, about 50%. Philips Lumileds has been working hard to increase conversion efficiency and make heat less and less, making heat dissipation design easier.
However, it is difficult to increase the degree of heat dissipation, because the sapphire substrate has its limitations, and it can be increased by 20%-30% in the future. In this case, 30-70% of the energy of white light will be converted into heat, so the heat dissipation is A long-standing problem. The problem of heat dissipation is how to dissipate heat from the solder joints of the chip to the air, and the heat transfer from the chip to the solder joints. The LED manufacturers have done a good job, and the thermal resistance from junction to solder joint is only 7°/w. Then we must start from the heat dissipation structure and heat dissipation material, we are very happy to see that some lighting manufacturers have done very well.
Finally, Dr. Sun Decai said that light quality, reliability, performance and cost are the most concerned places for Philips Lumileds. A good LED is not a high light efficiency. It is necessary to have light quality, reliability and cost performance for the end user.
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