LED display is promising because of its energy conservation, environmental friendliness and long service life. However, temperature is of great importance to LED screen. Temperature could shorten the life span of LED screen, decrease its light efficiency, set its color at variance and so on. Therefore, proper working temperature is vital to LED screen.
Five Impacts Temperature Has on LED Screen
1. Overtemperature Devastates LED display
1) When the working temperature is far higher than what the chips can bear, the light efficiency would decrease rapidly, which would lead to obvious luminous attenuation.
2) LED is usually packed with transparent epoxy. If the junction temperature is higher than the liquid-solid phase transition temperature(usually 125 ℃), the packing materials would become rubber-like with a surge in thermal expansivity, which would lead to open circuit and LED failure.
2. Overtemperature Shortens the Life Span of LED Display
The life span of LED screen appears as its luminous attenuation. Generally, the brightness decreases over time and finally goes out. Usually the service life of LED screen is defined as the span during which the brightness decreases by 30%.
Several Causes to the Luminous Attenuation of LED screen:
1) The defects of the LED chip would go wild at high temperature and intrude into the luminous zone and form many non-radiative recombination centers, which largely brings down the luminous efficiency. Besides, the microdefects of the materials and the rapidly expanding impurities from the boundaries and the electrical plates would also go into the lighting zone at high temperature, and thus form more than one deep level and speed up the luminous attenuation.
2) At high temperature, the transparent epoxy would denature and turn yellow, which leads to the decreasing light transmittance performance. The higher the temperature is, the faster the process will be.
3) Besides, the luminous attenuation of the fluorescent powder also matters as it gets dark sharply at high temperature.
Therefore, high temperature is the main factor that darken LED display and shorten the life span of LED display.
Usually different brands’ LED differs in luminous attenuation speed. Generally screen suppliers would offer the standard luminous attenuation curve graph. The luminous attenuation caused by high temperature is unrecoverable. The luminous flux before any unrecoverable deduction is defined as the initial luminous flux of LED screen.
3. High Temperature Reduce the Light Efficiency
Temperature affects LED screen in the following aspects.
1) As temperature rises, the density of electrons and holes would increase and the energy gap decrease, thus bringing down the migration rate of the electrons.
2) As temperature rises, the radiative recombination rate between the electrons and the holes inside the potential well goes down and causes nonradiative recombination(generating heat), and thus cut down the internal quantum efficiency of LED display.
3) As temperature goes high, the blue light wave crest moves along the long wave. In this situation, the emission wavelength of the chip and the excitation wavelength of the fluorescent powder cannot match with each other, which results in the decrease in the external light extraction efficiency of the LED display.
4) As temperature goes up, the quantum efficiency of fluorescent powder does down. In this way, the less light is emitted, which results in an decrease in the extraction efficiency of the external light.
5) The silica gel could be influenced a lot by the environment temperature. With the temperature going up, the thermal stress inside the silica gel will increase, cutting down the refraction of the silica gel and thus affect the light efficiency of the LED display.
4. The Impacts Temperature Has on LED Display
Generally, the emission wavelength consists of peak wavelength and main wavelength. The peak wavelength is the wavelength under the maximum light intensity. Meanwhile, the main wavelength is decided by the chromaticity coordinates, which reveals the human perception of color. Obviously, the change of the emission wavelength caused by the junction temperature would directly affect people’s perception of color. As for a certain component, the width of the forbidden band of the luminous materials would directly affect the LED in the emission wavelength or the color. With the temperature going up, the width of the forbidden band would reduce, for which the emission wavelength would get longer and the color would turn red.
5. Overtemperature will Restrict the Maximum Injection Current
Above are the main impacts temperature has on the LED display. From the introduction above we can know that high temperate could influence the screen a lot. Therefore, we should keep a proper temperature for the screen during the usage.
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