White LEDs can be much brighter than general LEDs and also have similar power consuming characteristics than fluorescent lamps, but on the basis of overcoming the following four shortcomings: a. temperature rising; b. unstable service life; c. need-to-be-improved luminous efficiency; d. the equalization of luminous characteristics; If we can start with the white high-brightness LED packaging structure, everything seems much easier.
The basic solution for the temperature rising problem is reducing the thermal resistance of the package; improving the chip shape, using small chips can sustain the lifetime of LEDs; there are also some specific methods for equalizing the luminous characteristics of LEDs. Generally, LEDs generated after 2005 can improve their performances though above methods.
There are many other methods to increase the lifetime of LEDs, for example, using siliceous sealing materials and ceramic packaging materials can increase LEDs’ lifetime by 10%, especially useful for white LEDs (which spectrum contains wavelength below 450nm). Short-wavelength rays can easily cause damages to traditional epoxy resin sealing materials. White high-brightness LED packaging structure will speed up this process. According to industrial tests, after approximate 10,000-hour continuous lighting, the brightness of high-power white LED applications usually reduced by more than 50%, which can hardly meet the basic requirements for long-term lighting.
Improving chip packaging structure can improve the luminous efficiency of high-power white LED products, achieving the same level of low-power LED products. Basically, when the current density is increased by more than 2 times, the extraction of light from high-power LED chips will become more difficult, leading to the dilemma that the luminous efficiency of high-power white led tunnel light is much lower than that of low-power white LEDs. In theory, improving the electrode structure of chips can solve the extraction problem mentioned above.
About the equalization of light-emitting characteristics, it is generally believed that improving the uniformity of material (phosphor) density and production technologies of phosphor can overcome this distress. We need also reduced the thermal impedance of white high-brightness LED packaging structure to improve the heat dissipation process, as well as increase the input voltage: a. reduce chip-to-package thermal impedance; b. suppressing the thermal impedance from package to PCBs; c. smooth chips’ cooling performances.