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Sep 28,2021| LED Knowledge
Outdoor LED displays have broad development prospects due to their energy saving, environmental protection, and long service life. However, due to the poor heat dissipation materials of some manufacturers' outdoor LED displays, there are not many problems caused. Although the LED display itself has a certain heat dissipation function, in fact, the heat dissipation problem is mainly caused by high temperature. Do you know how much damage high temperatures can bring to LED electronic displays? Let's take a look at the damage caused by high temperature to outdoor led display belts.
1. Too high temperature will cause the outdoor LED display to be completely damaged
(1) The operating temperature of the LED electronic display screen exceeds the carrying temperature of the chip, which will cause the luminous efficiency of the LED display screen to drop rapidly, causing obvious light attenuation and damage;
(2) LED electronic displays are mostly packaged with 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 short-circuit and damage.
2. Temperature rise will shorten the life of LED electronic display
The life of the LED electronic display is characterized by its light attenuation, that is, the time is long and the brightness is getting lower and lower, until it finally goes out. The time for the luminous flux of an LED display to decay by 30 is usually defined as its lifetime.
The reasons for the light decay of outdoor LED display are as follows:
(1) The defects in the LED display chip material will spread rapidly at higher temperatures. , Copy until it invades the light-emitting area, forming a large number of non-radiative recombination centers, which seriously reduces the luminous efficiency of the LED electronic display. In addition, under high temperature conditions, small defects in materials and rapid expansion of impurities from the interface and circuit boards will also be introduced into the light-emitting area, forming a large number of deep layers, which will also accelerate the attenuation of light. LED display equipment.
(2) Under high temperature, the transparent epoxy resin becomes yellowish, which affects its light transmission performance. The higher the working temperature, the faster the process will proceed. This is another main reason for the light attenuation of the LED electronic display.
(3) The light attenuation of the phosphor is also the main cause of the light attenuation of the outdoor LED display, because the phosphor will be very attenuated at high temperatures.
Therefore, high temperature is the main source of light attenuation for outdoor LED displays and shortens the life of LED electronic displays.
The light attenuation of outdoor LED displays of different brands is different. Usually, LED display manufacturers will give a set of standard light attenuation curves. The attenuation of the luminous flux of the LED display screen caused by the high temperature cannot be recovered. The LED display has no beam before the irreversible light attenuation, which is called the "initial beam" of the LED electronic display.
3. High temperature will reduce the luminous efficiency of outdoor LED displays:
(1) As the temperature increases, the concentration of electrons and holes increases, the band gap decreases, and the electron mobility decreases.
(2) When the temperature rises, the possibility of recombination of electrons and holes in the potential well decreases, leading to non-radiative recombination (heating), 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, so that the emission wavelength of the chip does not match the excitation wavelength of the phosphor, and the white external light extraction efficiency LED display is also reduced.
(4) As the temperature increases, the quantum efficiency of the phosphor decreases, the light emission decreases, and the external light extraction efficiency of the LED display panel 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, causing the refractive index of the silica gel to decrease, thereby affecting the light efficiency of the LED display.
4, the impact of high temperature on the wavelength (light color) of the LED electronic display
The wavelength of outdoor LED display is usually divided into peak wavelength and dominant wavelength. The peak wavelength, that is, the light intensity is the maximum wavelength, and the dominant wavelength can be determined by the X and Y chromaticity coordinates to reflect the color perceived by the human eye. Obviously, the change in the wavelength of the LED display screen caused by the junction temperature will directly cause the human eyes to perceive the color of the LED display screen to be different.
For LED display devices, the band gap of the luminescent material directly determines the wavelength or color of the device. As the temperature increases, the band gap of the material will decrease, resulting in a longer wavelength of the device and a red shift in color.
Finally, high temperature will limit the maximum injection current of the LED display. The above points are the introduction of the impact of high temperature on the outdoor LED display. We can know that the high temperature has a huge impact on the LED electronic display. So choosing the right temperature is the focus of outdoor LED display.