First, the temperature is too high, which will cause damage to the display.
(1) LED display screen is mainly packaged in transparent epoxy resin. If the junction temperature exceeds the solid phase transition temperature (usually 125 ° C), the packaging material will become rubber and the coefficient of thermal expansion will rise sharply, causing the LED display to open and fail.
(2) The operating temperature of the LED display exceeds the carrying temperature of the chip, resulting in a rapid decline in the luminous efficiency of the LED display, resulting in significant light attenuation and damage; secondly, an increase in temperature will reduce the luminous efficiency of the LED display.
Second, the temperature affects the light efficiency of the LED display, including the following:
(1) When the temperature rises, the possibility of recombination of electrons and holes in the potential well is reduced, resulting in non-radiative recombination (heat generation), thereby reducing the internal quantum efficiency of the LED display.
(2) The temperature rise causes the blue peak of the chip to move in the long-wave direction, which makes the emission wavelength of the chip do not match the excitation wavelength of the phosphor, and also causes the external light extraction efficiency to decrease.
(3) As the temperature increases, the concentration of electrons and holes increases, the band gap decreases, and the electron mobility decreases.
(4) The performance of silica gel is greatly affected by the ambient temperature. As the temperature increases, the thermal stress in the silica gel increases, causing the refractive index of the silica gel to decrease, thereby affecting the light efficiency of the LED display.
(5) As the temperature increases, the quantum efficiency of the phosphor decreases, the luminescence decreases, and the external light extraction efficiency of the LED display panel decreases.
Third, the temperature rise will shorten the life of the LED display
The life of an LED display is characterized by light attenuation, that is, for a long time, the brightness is getting lower and lower until it is finally extinguished.
The reasons for the LED display light decay are as follows:
(1) At high temperatures, the transparent epoxy resin denatures and turns yellow, which affects its light transmission. The higher the operating temperature, the faster the process proceeds. This is another major cause of LED display attenuation.
(2) The defects existing in the LED display chip material will rapidly proliferate and multiply at higher temperatures until invading the illumination area, forming a large number of non-radiative composite centers, which seriously reduces the luminous efficiency of the LED display. In addition, under high temperature conditions, micro-defects in the material and rapidly expanding impurities from the interface and the plate will also be introduced into the illumination area, forming a large number of deep layers, which will also accelerate the light attenuation of the LED.
(3) The light attenuation of the phosphor is also a major factor affecting the light attenuation of the LED display, because the attenuation of the phosphor at high temperatures is very serious.
Therefore, high temperature is the main reason for the reduction of LED display fading, shortening the life of LED display. .
Fourth, too high a temperature limits the maximum injection current of the display.
Fifth, the effect of temperature on the LED display wavelength (light color)
The illumination wavelength of an LED display can generally be divided into a peak wavelength and a dominant wavelength. The peak wavelength is the wavelength with the highest light intensity, and the dominant wavelength can be determined by the X, Y chromaticity coordinates, reflecting the color perceived by the human eye. Obviously, the change in wavelength of the LED display caused by the junction temperature will directly make the human eye feel the different colors of the LED display. For LED display devices, the forbidden band width of the luminescent material directly determines the wavelength or color of the device. As the temperature increases, the forbidden band width of the material will decrease, resulting in a longer wavelength of the device and a red shift in color.