How does the luminous efficiency of white LEDs increase?

In the past, LED manufacturers have developed large-size LED chips in order to obtain sufficient white-light patch LED beams. In this way, the LED chips are trying to achieve the desired goals. However, when the power applied by the white-strip LEDs continues to exceed 1 W, the light beams will decrease. The relative reduction of 20 to 30%, in other words, if the brightness of white LEDs is several times larger than that of conventional LEDs, and the power consumption characteristics are expected to exceed fluorescent lamps, it is necessary to overcome the following four major problems, including: suppressing temperature rise and ensuring white light. LED lifetime, improved luminous efficiency, and equalization of luminescence properties.

The specific method for temperature rise is to reduce the thermal impedance of the package; the specific method for maintaining the service life of the white LED is to improve the chip shape and use a small chip; to improve the luminous efficiency of the white LED, the specific method is to improve the chip structure and adopt a small chip; As for the specific method of uniformizing the luminescent characteristics, an improved packaging method for white-light patch LEDs has been developed.

Is the fundamental way to solve the heat problem package: due to the increased power it will cause thermal impedance of the package fell sharply 10K / W or less, foreign operators have developed high-temperature white SMD LED would try to improve these problems, but in fact large The power of the power LED is several times higher than that of the low-power LED, and the temperature rise will cause the luminous efficiency to drop sharply. Even if the packaging technology allows high heat, the bonding temperature of the LED chip may exceed the allowable value. Finally, the operator finally It is understood that solving the heat dissipation problem of the package is the fundamental method.

The service life of white LEDs, such as the use of silicon packaging materials and ceramic packaging materials, can increase the lifetime of white LEDs by a single digit, especially the white LED's emission spectrum contains short wavelengths of light below 450nm. The epoxy resin encapsulation material is easily destroyed by short-wavelength light. The large amount of high-power white LEDs accelerates the degradation of the packaging material. According to the test results of the industry, the continuous lighting is less than 10,000 hours, and the brightness of the high-power white-light patch LED has been reduced. More than half of the basic requirements for the long life of the illumination source cannot be met.

Regarding the luminous efficiency of the white-light patch LED, and improving the chip structure and package structure, the same level as the low-power white LED can be achieved. The main reason is that when the current density is increased by more than 2 times, it is not easy to take out light from a large chip, but the result will instead The luminous efficiency is not as good as that of the low-power white-light patch LED. If the electrode structure of the chip is improved, the above-mentioned light-taking problem can be solved theoretically.