When the LED is used in the 60's, the past due to use of the power LED is not high, only used as the display lights and signal lights, the package did not have heat issues, but in recent years for use in backlighting LED, the brightness and power are continued to be the raised heat LED lighting industry has become the most important issue.
LED mass production and is widely used, its brightness to the speed of rapid increase, from 2001 to 25 lm / W, 2006 年 6 announced the day of Asian Chemical Industry Laboratory of up to 134 lm / W, 2007 年 2 月 Lumileds Companies can reach 115 lm / W, 2008 年 7 月 OSRAM development can be achieved is 136 lm / W of LED, Cree laboratory in November 2008 of up to 161 lm / W, progress to early 2009, Nichia Chemical Industries published The luminous efficiency has up to 249 lm / W, while the mass production of LED in 2010 broke through 100 lm / W of the level.
Development based on observation over the past 30 years, LED, Lumileds Lighting Company in 2003, Mr. Roland Haitz summarized LED sector Moore (Moore) law-Haitz's law (Figure 1), indicating LED approximately every 18 to 24 months to improve twice the brightness, as Theorem LED brightness can be estimated 10 years, then increase by 20 times, 90% of the cost will be reduced in order to achieve completely replace the existing lighting technology, LED lighting, hot in recent years has been of great importance and .
LED backlight
LED for low power consumption, mercury, long life, small size, reduced carbon dioxide emissions and other advantages to attract domestic and foreign companies strongly promote the replacement of existing lighting. LED lighting can be divided into the main display backlighting, automotive lighting, traffic lights and indoor and outdoor lighting, and backlight modules in 2009 is widely used in notebook panel, then will gradually be used to the home TV, its about accounted for 50% of the panel module manufacturing cost component of about 70% of the display and consumption of energy, so the backlight for the display panel of the most important key. However, LCDs can not self-luminous and therefore require backlight module as a source of light, so the backlight is good or bad results will affect the show even drama. Plus panels of factors to be thin, so much as to CCFL backlight lamps, and LED backlight compared to CCFL has good color rendering, long life, fast response, and other advantages (Table 1).
Coupled with the promotion of environmental issues in recent years due to the global, national environmental policies the government ban of mercury, such as the WEEE and RoHS EU directives and China's electronic information products such as pollution control measures start to implement, but also driven by the small size of the LED as an alternative package The best non-mercury source of CCFL. Also, because the LED luminous efficiency of the unit cost of continued rapid growth, making the LED decreases the cost of expanding, narrowing the price gap between CCFL and LED also contributed significantly to import LED panel makers started in backlight module.
LED thermal problems
Currently there are two ways to improve LED brightness, respectively, in order to increase chip brightness and more stars tightly arranged, etc., these methods are required to enter a higher power of the energy, the energy input LED, about 20% will be converted into light, and the remaining 80 % are converted into heat energy, then the double single package into the current, heat will naturally doubled, so the heat in such a small area, the heat problem will gradually worsen. If this package is only used in only 1 to 4 LED lights astigmatism, astigmatism lamp time is short, so the heat accumulation is not obvious; such as backlighting applications in LCD TVs, and even the use of high brightness LED, but also intensive arranged and lit a long time, so in the limited space for heat dissipation is difficult to timely exclude these hot outside.
Unfortunately, the generated heat, the grain is a very serious problem. When the grain interface temperature increases, the quantum down conversion efficiency of photoluminescence intensity, and the decline in life expectancy will follow; emission wavelength change, making the color stability was reduced; thermal expansion due to different coefficients of different materials, there will be cumulative thermal stress to reduce product reliability, service life will be reduced. Therefore, the cooling of high power LED is very important problem to be solved.
The thermodynamic
73% of the traditional incandescent light to infrared radiation heat the way, you can feel the heat in the surrounding high fever, body heat accumulation phenomenon so small bulbs, and LED light generated, mostly in the majority of visible or ultraviolet light, radiation methods can not heat dissipation, because of the smaller LED package, it is difficult to shed heat, resulting in the quality of LED lighting have a big problem, which is that LED thermal problems to be solved urgently.
LED thermal management in the discussion of issues before the first need to understand basic thermodynamics. Basically there are 3 ways heat (Table 2), namely "heat conduction", "convection cooling" and "radiant heat" from the theoretical formula of the above three can be analyzed, the main trouble spots in heat "area"; addition, because of radiation near room temperature due to heat dissipation case are very small, so the most important way to discuss the heat conduction and convection in two ways.
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