The effect of high temperature on led display
1. Excessive temperature will lead to the complete destruction of the LED display
(1) If the working temperature of the LED display exceeds the bearing temperature of the chip, the luminous efficiency of the LED display will decrease rapidly, resulting in obvious light decay and damage;
(2) The LED display is mostly encapsulated with transparent epoxy resin. If the junction temperature exceeds the solid phase transition temperature (usually 125°C), the encapsulation material will change to a rubbery state and the thermal expansion coefficient will rise sharply, resulting in an open circuit and failure of the LED display. .
2. The increase in temperature will shorten the life of the led display
The life of the led display is manifested in its light decay, that is, the brightness will become lower and lower over time, until it finally goes out. It is usually defined that the time when the luminous flux of the LED display screen decays by 30 is its life.
Usually the reasons for the light failure of LED display are as follows:
(1) Defects in the LED display chip material will multiply and multiply rapidly at higher temperatures until they invade the luminous area, forming a large number of non-radiative recombination centers, which seriously reduces the luminous efficiency of the LED display. In addition, under high temperature conditions, micro-defects in the material and fast-expanding impurities from the interface and the board will also be introduced into the light-emitting area, forming a large number of deep energy levels, which will also accelerate the light decay of the LED display device.
(2) The transparent epoxy resin will denature and turn yellow at high temperature, which will affect its light transmission performance. The higher the working temperature, the faster this process will proceed, which is another main reason for the light decay of the LED display.
(3) The light decay of the phosphor is also a major factor affecting the light decay of the LED display, because the decay of the phosphor at high temperature is very serious.
Therefore, high temperature is the main source of light failure of LED display and shortening the life of LED display.
The light decay of different brands of LED displays is different. Usually, LED display manufacturers will give a set of standard light decay curves. The luminous flux attenuation of the LED display screen caused by high temperature is irreversible, and the luminous flux of the LED display screen before irreversible light attenuation does not occur, which is called the “initial luminous flux” of the LED display screen.
3. The increase in temperature will reduce the luminous efficiency of the LED display
The reasons why temperature affects the light efficiency of LED displays include the following aspects:
(1) As the temperature increases, the concentration of electrons and holes will increase, the band gap will decrease, and the electron mobility will decrease.
(2) As the temperature increases, the probability of radiative recombination of electrons and holes in the potential well decreases, resulting in non-radiative recombination (generating heat), thereby reducing the internal quantum efficiency of the LED display.
(3) The increase in temperature causes the blue light wave peak of the chip to shift to the long wave direction, which makes the emission wavelength of the chip and the excitation wavelength of the phosphor do not match, and also causes the external light extraction efficiency of the white LED display to decrease.
(4) As the temperature rises, the quantum efficiency of the phosphor decreases, the light output decreases, and the external light extraction efficiency of the LED display decreases.
(5) The performance of silica gel is greatly affected by the ambient temperature. As the temperature increases, the thermal stress inside the silica gel increases, resulting in a decrease in the refractive index of the silica gel, thus affecting the light efficiency of the LED display.
4. The effect of temperature on the luminous wavelength (light color) of the LED display
The luminous wavelength of LED display can generally be divided into peak wavelength and dominant wavelength. The peak wavelength is the wavelength with the maximum light intensity, and the main wavelength can be determined by the X and Y chromaticity coordinates, reflecting the color perceived by the human eye. Obviously, the change in the luminous wavelength of the LED display caused by the junction temperature will directly cause the human eye to have different perceptions of the luminous color of the LED display. For an LED display device, the value of the forbidden band width of the material in the light-emitting region directly determines the wavelength or color of the device’s light emission. As the temperature increases, the forbidden band width of the material will decrease, resulting in a longer wavelength of light emission of the device and a red shift of the color.
5. Excessive temperature will limit the maximum injection current of the led display