1. Excessive temperature will lead to the complete destruction of the led display
(1) The operating temperature of the led display screen will exceed the load temperature of the chip, which will rapidly reduce the luminous efficiency of the led display screen, causing obvious light attenuation and causing damage;
(2) LED display screens are mostly encapsulated with transparent epoxy resin. If the junction temperature exceeds the solid phase transition temperature (usually 125°C), the packaging material will transform into rubber and the thermal expansion coefficient will rise sharply, resulting in open circuit and failure of the led display screen. .
Second, the temperature rise will shorten the life of the led display
The lifespan of the led display is shown by its light decay, that is, the brightness becomes lower and lower as time goes by, until it finally goes out. It is generally defined that the time when the luminous flux of the led display screen decays by 30 is its life.
Generally, the reasons for the light decay of the led display are as follows:
(1) The defects in the LED display chip material will rapidly multiply and multiply at higher temperatures, until it invades the light-emitting area, forming a large number of non-radiative composite centers, and seriously reducing 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 electric plate 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. This is another main reason for the light decay of the LED display.
(3) The light decay of phosphors is also a main reason that affects the light decay of LED displays, because the decay of phosphors is very serious at high temperatures.
Therefore, high temperature is the main source of led display light decay and shortening the life of the led display.
The light attenuation of different brands of led displays is different, usually led display manufacturers will give a set of standard light attenuation curve. The attenuation of the luminous flux of the led display screen caused by high temperature is unrecoverable. The luminous flux before the unrecoverable light attenuation of the led display screen is called the "initial luminous flux" of the led display screen.
Third, the increase in temperature will reduce the luminous efficiency of the led display
The reasons why temperature affects the light effect of LED display include the following aspects:
(1) As the temperature rises, the concentration of electrons and holes will increase, the band gap will decrease, and the electron mobility will decrease.
(2) As the temperature rises, the probability of radiation 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.
(3) The temperature rise causes the blue 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 not match, and also causes the reduction of the external light extraction efficiency of the white light LED display.
(4) As the temperature rises, the quantum efficiency of the phosphor powder decreases, the light output decreases, and the external light extraction efficiency of the LED display screen decreases.
(5) The performance of silica gel is greatly affected by ambient temperature. As the temperature rises, the thermal stress inside the silica gel increases, causing the refractive index of the silica gel to decrease, thereby affecting the light efficiency of the LED display.
Fourth, the influence of temperature on the luminous wavelength (light color) of the led display
The emission 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 dominant wavelength can be determined by the X and Y chromaticity coordinates, reflecting the color perceived by the human eye. Obviously, the change in the light-emitting wavelength of the led display screen caused by the junction temperature will directly cause the human eyes to have different perceptions of the light-emitting color of the led display screen. For a LED display device, the band gap value of the material in the light-emitting region directly determines the wavelength or color of the device's light emission. As the temperature rises, the band gap of the material will decrease, which will cause the device to emit longer wavelengths and red shift the color.
