Nov 08.2019

What is the impact of LED display working at high temperature?

In normal conditions, an indoor LED display can cool itself due to its low brightness and less heat it produces. However, an outdoor LED display has to cool itself through an air conditioner or an axial flow fan due to its higher brightness and more heat it produces. As the LED display is one of the electronic products, the increasing temperature has an impact on its light attenuation, driver IC efficiency and service life, etc. Let's know the impact of LED working in high temperature in detailed.

 

 

1. The open circuit and failure of LED displays

 

If the working temperature of the LED display exceeds the bearing temperature of the chip, its luminous efficiency will be rapidly reduced, resulting in obvious light attenuation and damage. 

 

LED displays are mostly encapsulated with transparent epoxy resin. If the junction temperature exceeds the solid phase transition temperature (usually 125℃), the encapsulation material will be turned into the rubber-like condition and the coefficient of thermal expansion will rise sharply, resulting in the open circuit and failure of LED displays.

 

2. Excessive temperature affects the light attenuation of LED displays

 

The light attenuation presents the life of LED displays. That is to say, as time goes on, the brightness will be increasingly lower until it dies out. Generally, the life of LED displays​ is defined as the time span, during which the luminous flux decreases by 30. High temperature is the main cause of the light attenuation and the shortening life of LED displays. The light attenuation varies among different brands of LED displays. 

 

Usually, LED display manufacturers will give a set of standard light attenuation curves. The luminous flux attenuation of LED displays caused by high temperature is irreversible. The luminous flux before the irreversible light attenuation of LED displays is called the "initial luminous flux" of LED displays.

 

3. Excessive temperature decreases the light-emitting efficiency of LED displays

 

As the temperature rises, the concentration of electrons and electron holes will increase, the band gap will be shortened, and the electron mobility will decrease. As the temperature rises, the radiative recombination probability of electrons and electron holes in the potential well will decrease, resulting in non-radiative recombination (generating heat), thus reducing the internal quantum efficiency of the LED display. 

 

The rise of temperature will move the chip's crest of blue light towards the direction of long waves, causing a mismatch between the emission wavelength of the chip and the excitation wavelength of the fluorescent powder, and a reduction of the light extraction efficiency outside the white LED display. 

 

As the temperature rises, the quantum efficiency of the fluorescent powder will decrease, leading to less light emission, and the external light extraction efficiency of the LED display will decrease. The performance of silica gel is greatly affected by the ambient temperature. As the temperature rises, the thermal stress inside the silica gel will increase, resulting in a decrease of its refractive index, thus affecting the lighting efficiency of the LED display.