How high heat affect full colour LED display? How importance of the heat dissipation of LED display? We introduces the principles and reasons today for you to understand it better and help to prolong the service life of your LED display screen better!
Nowadays, with the increasing use of led display screens,LED display users should have a certain understanding of the maintenance of the led display screen, in order to maximize the advantages of the display screen.
Whether it is an indoor LED display or an outdoor LED display, heat will be generated during operation, and the heat generated will cause the temperature of the LED display to rise.
Generally speaking, indoor LED displays generate less heat due to low brightness and can dissipate naturally. Outdoor LED displays generate a lot of heat due to their high brightness, and need to be dissipated by air conditioners or axial fans.
For users of large LED screens, we must pay attention to the temperature changes of large LED screens, because the high temperature has the following four effects on LED display screens:
1. Damage to Components of Full Colour LED Display
(1) The working temperature of the led display screen exceeds the load temperature of the led chip, which will rapidly reduce the luminous efficiency of the led display screen, produce obvious light attenuation, and cause damage to the chip;
(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 an open circuit and failure of the led display screen.
2. Shorten the Working Time of Full LED display
The life of the led display is represented by its light decay, that is, as time goes by, the brightness becomes lower and lower until it goes out.
According to data from a laboratory in the United States, the junction temperature increased from 63C to 74C, and the LED lifetime decreased from 36,000 hours to 16,000 hours.
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 the higher temperature, until they invade the light-emitting area, forming a large number of non-adversative 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) 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 luminous decay of phosphors is also a major factor affecting the luminous decay of LED display screens, 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 curves.
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.
3. Reduce the Luminous Efficiency of LED Full Color Display
(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 rises, the probability of radiation recombination of electrons and holes in the potential well is reduced, resulting in non-adversative 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 screen.
(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.
4. Affect the Light Color (Luminous Wavelength)
The emission wavelength of the led display can generally be divided into peak wavelength and dominant wavelength. The peak wavelength is the wavelength of light intensity, and the dominant wavelength can be determined by the X and Y chromatically 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.
Wavelength drift will cause problems in color correction. The wavelength drift of the LED is relatively large at low and high temperatures.
According to experimental data, for every degree of temperature change, the wavelength changes by 0.2-0.3nm. And output brightness reduction: every degree Celsius temperature change results in a 1% change in output brightness, of which the red light is the most affected.
From -40 degrees 180% brightness, to 120 degrees brightness is less than 50%, that is to say, the brightness of the red light is reduced by nearly two-thirds. Relatively speaking, the brightness of blue light and green light has less temperature influence, especially blue light.
When the temperature rises, there is a problem. The brightness of LEDs of different colors is different.
Today we disccussed how important the heat dissipation for full colour display is, and four damages the high heat will cause to the LED displays. Hope it can help you! For more useful and practicle knowledge of LED display, welcome turn to our LED FAQ page!