The basic structure of LED is a P-N junction of a semiconductor. The experiment points out that when the current flows through the LED element, the temperature of the P-N junction will rise. In strict sense, the temperature of the P-N junction region is defined as the junction temperature of LED. Usually, because the chip of the component has a very small size, we can regard the temperature of the LED chip as junction temperature. So the size of the 5730 bulb and the 2835 bulb is directly related to the heat dissipation of the lamp.
The harm of LED junction temperature:
(1) the increase of temperature will shorten the life of LED
The life span of LED is characterized by its decay of light, that is, the longer the time is, the lower the luminance is, until the final extinction. It is usually defined that the lifetime of LED luminous flux attenuation is 30%.
(2) high temperature will cause permanent damage to LED
LED is encapsulated more with silica gel. If the junction temperature exceeds the solid phase transition temperature (usually 125 C), the packaging material will change to the rubber and the thermal expansion coefficient rises suddenly, which leads to the opening and failure of the LED.
(3) the increase of temperature will reduce the luminous efficiency of LED
As the temperature increases, the radiation recombination probability of electrons and holes in the potential well decreases, resulting in non radiative recombination (generating heat), thereby reducing the internal quantum efficiency of LED a..
With the increase of B. temperature, the concentration of electrons and holes will increase, the forbidden band width will decrease, and the electron mobility will decrease.
C. with the increase of temperature, the quantum efficiency of phosphor is reduced, the light emission is reduced, and the external light extraction efficiency of LED is reduced.
The properties of D. silica gel are greatly influenced by ambient temperature. With the increase of temperature, the thermal stress inside silica gel increases, leading to a decrease in the refractive index of silica gel, thereby affecting LED.