The effect of temperature on the screen and the solution

Whether it is an indoor LED display or an outdoor LED display, heat is generated during operation, and the generated heat will cause the temperature of the LED display to rise. But what is the effect of the display under high-temperature working conditions?

1. The working temperature of the LED display exceeds the load temperature of the chip, which will rapidly reduce the luminous efficiency of the LED display, cause obvious light attenuation, and cause damage; the LED display is mostly encapsulated with transparent epoxy resin if the junction temperature exceeds the solid At the phase transition temperature (usually 125°C), the packaging material will transform to a rubbery shape and the thermal expansion coefficient will rise sharply, which will cause the LED display to open and fail.

2. Excessive temperature will affect the light decay of the LED display screen. The lifespan of the led display is shown by its light decay, that is, the brightness becomes lower and lower as time passes 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. High temperature is the main source of led display light decay and shortens the life of the led display. The light attenuation of different brands of led displays is different and 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.

Third, the increase in temperature will reduce the luminous efficiency of the led display. As the temperature rises, the concentration of electrons and holes will increase, the bandgap will decrease, and the electron mobility will decrease; as the temperature rises, the probability of radiation recombination of electrons and holes in the potential well decreases, resulting in non-radiative recombination. Heat), thereby reducing the internal quantum efficiency of the LED display; the increase in temperature 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 do not match, which will also cause the external light of the white LED The extraction efficiency is reduced; 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; the performance of the silica gel is greatly affected by the environmental 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 screen. The emission wavelength of led display can generally be divided into peak wavelength and dominant wavelength. The peak wavelength is the wavelength with the greatest 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 an LED display device, the bandgap value of the material in the light-emitting zone directly determines the wavelength or color of the device's light emission. As the temperature rises, the bandgap of the material will decrease, which will cause the device to emit longer wavelengths and red shift the color.

5. Excessive temperature will limit the maximum injection current of the led display. When purchasing an LED display, pay attention to choosing the LED display chip brand, packaging manufacturer, driver IC brand, and switching power supply brand. The quality of the brand will affect the quality of the LED display itself, and the brand is high. The product itself generates less heat and can better control the temperature of the LED display, thereby extending the life of the LED display.

LED display has great development prospects due to its advantages of energy-saving, environmental protection and long life. LED display screens are more sensitive to temperature: it will affect the life of the LED display screen, light efficiency, color, etc. So the right temperature is very important for the LED display.

The working environment of the LED display is extremely complex. The indoor LED display is not exposed to direct sunlight and with air conditioning installed indoors. The working pressure is smaller.

The outdoor LED display is usually installed on the columns or roofs of buildings or squares, In summer, it is exposed to direct sunlight and extremely high temperature. In winter, it is tested by severe cold. In some areas, the temperature can be as low as - 40 ℃ in winter. It is a great test for plastic parts and protective glue of the LED display screen. In addition, the working temperature of the special power supply for the LED display screen is - 20-40 ℃. In low-temperature countries, the low-temperature power supply is used when purchasing an LED display screen. The working temperature is limited to - 40 ℃. Generally, the storage temperature of the LED display screen can reach - 50-60 ℃, and the working temperature is recommended to be - 20-30 ℃. Any product will expand with heat and contract with cold.

Good LED display screen manufacturers will do high and low-temperature tests. It is recommended that users pay attention to product performance indicators when purchasing LED display screens, and not deliberately pursue low prices.

The influence of high temperature on LED display are the following 5 points:

1, High temperature will lead to complete destruction of LED display

(1) When the working temperature of the LED display exceeds the chip's carrying temperature, the luminous efficiency of the LED display will decrease rapidly, which will cause obvious light decay and damage;

(2) Most LED display screens are encapsulated with transparent epoxy resin. If the junction temperature exceeds the solid phase transition temperature (usually 125 ℃), the packaging material will change to rubber shape and the coefficient of thermal expansion will rise abruptly, which will lead to an open circuit and failure of the LED screen.

2, Temperature rise will shorten the life of the LED display

The life span of LED display is represented by its light decay, that is to say, when the time is long, the brightness becomes lower and lower until it goes out. Generally, it is defined as the life of an LED display screen when the luminous flux decays by 30.

Generally, the causes of LED display light failure are as follows:

(1) The defects in LED display chip materials will proliferate at a high temperature until they invade into the light-emitting area, forming a large number of nonradiative composite centers, and seriously reducing the light-emitting efficiency of LED display. In addition, at high temperature, the micro defects in the material and the fast-expanding impurities from the interface and the electric plate will also be introduced into the light-emitting region, forming a large number of deep energy levels, which will also accelerate the light decay of LED display devices

(2) When the temperature is high, the transparent epoxy resin will change and turn yellow, which will affect its light transmission performance. The higher the working temperature, the faster the process will go on, which is another main reason for the light failure of the LED display screen.

(3) The light decay of phosphor is also one of the main reasons that affect the light decay of the LED display screen because the decay of phosphor is very serious at high temperatures.

Therefore, high temperature is the main cause of LED display light decay and shortening the life of the LED display.

The light attenuation of different brands of the LED display screen is different. Usually, the manufacturer of the LED display screen will give a set of standard light attenuation curve. High temperature led to LED display light flux attenuation is not recoverable, LED display does not occur before the irrecoverable light attenuation of the light flux, known as the "initial light flux" of LED display.

3, Temperature rise will reduce the luminous efficiency of LED display

The reasons why temperature affects the light efficiency of LED display include the following aspects:

(1) With the increase of temperature, the electron mobility will decrease.

(2) With the increase of temperature, reducing the internal quantum efficiency of the LED display screen.

(3) As the temperature increases, the blue wave peak of the chip shifts to the long-wave direction, which makes the emission wavelength of the chip and the excitation wavelength of the phosphor mismatch, and also causes the reduction of the external light extraction efficiency of the white LED display.

(4) With the increase of temperature, the quantum efficiency of phosphor decreases, the output light decreases, and the external light extraction efficiency of the LED display screen decreases.

(5) The performance of silica gel is greatly affected by the ambient temperature. With the increase of temperature, the thermal stress inside the silica gel increases, resulting in a decrease of the refractive index of silica gel, which affects the light efficiency of the LED display screen.

4, The influence of temperature on the light wavelength (light color) of LED display

Generally, the luminous wavelength of LED displays can be divided into peak wavelengths and main wavelengths. The peak wavelength is the wavelength of light intensity * and the main wavelength can be determined by X and Y chromaticity coordinates, reflecting the color perceived by the human eye. Obviously, the change of LED display's luminous wavelength caused by junction temperature will directly create a different feeling of eyes on the LED display's luminous color. For an LED display device, the bandgap width of the light-emitting materials directly determines the wavelength or color of the device. With the increase of temperature, the bandgap width of the material will decrease, resulting in the longer wavelength, and the redshift of the color of the device.

5, The too high temperature will limit the injection current of LED display.

The above points are the impact of high temperature on the LED display. Through the above introduction, we can know that the impact of temperature rise on LED display is very large.

How to solve the problem of high-temperature LED display? The common methods of heat dissipation are as follows:

1. Fan cooling, long-life, and high-efficiency fan is used to strengthen the cooling inside the lamp shell. This method has low cost and good effects.

2. It is a common way to use aluminum fins as a part of the shell to increase the cooling area.

3. Air hydrodynamics, the use of lamp shell shape, to create convection air, which is a low-cost way to strengthen heat dissipation.

4. Surface radiation and heat dissipation treatment, the surface of the lamp shell is treated with radiation and heat dissipation treatment, the simpler is to apply radiation and heat dissipation paint, which can take the heat away from the surface of the lamp shell by radiation.

5. Integration of heat conduction and heat dissipation -- the application of high thermal conductivity ceramics. The purpose of light shell heat dissipation is to reduce the working temperature of the LED high-definition display screen chip. Because the expansion coefficient of the LED chips is very different from that of our usual metal heat conduction and heat dissipation materials, it is not allowed to weld the LED chip directly to avoid high and low-temperature thermal stress damaging the chip of LED display screen.

6. Heat conduction tube is used for heat dissipation. Heat is transferred from an LED display chip to shell fins by heat conduction tube technology.

7. The heat-conducting plastic shell is filled with heat-conducting materials when the plastic shell is injected, so as to increase the heat conducting and radiating capacity of the plastic shell.

8. The integration of heat conduction and heat dissipation - the application of high thermal conductivity ceramics, the purpose of light shell heat dissipation is to reduce the working temperature of the LED display screen chip. Because the expansion coefficient of the LED chip is very different from that of our usual metal heat conduction and heat dissipation materials, it is not allowed to weld the LED chip directly, so as to avoid high and low-temperature thermal stress damaging the chip of LED display screen.

Then what's the effect of low temperature on LED display?

In some countries or regions, most of the temperature is below 0 ℃ throughout the year, and even below - 30 ℃ at night. When the ambient temperature of the LED display screen in this area is too low, the power-on of the display screen will be unsuccessful. 

For the outdoor LED display screen, cold winter is a long and severe test, because under the temperature of minus 20 degrees, all kinds of materials of LED display screen are different due to their different thermal expansion and contraction coefficient, and their physical size changes are not consistent, which is easy to appear large gap or extrusion and bulge or even burst between modules, resulting in the failure of waterproof and dustproof LED display screen and obvious mosaic Phenomenon.

In addition, in the case of extremely low temperatures, some electronic components can not work normally, so that the whole screen can not work normally. Through the complete limit temperature simulation environment test, our company's outdoor LED display screen has passed the test of - 35 ℃ ~ 85 ℃ simulation temperature and humidity test room before leaving the factory. We have fully considered the harsh environment that the display screen may bear in the future and made corresponding measures, no matter from the display screen's iron box, lamp tube, electronic components, or the bottom shell mask, etc The careful choice of points. For ultra-low temperature led display design, our company has formed a unique solution.

1. Using ultra-low temperature power supply: Meanwell ultra-low temperature power supply, Powerld ultra-low temperature power supply, etc. can achieve - 40 ℃; start at - 25 ℃. Among them, when the low-temperature environment is close to the temperature limit of the power supply (for example, the ultra-low temperature is adopted at - 35 ℃), the load power of the power supply will be derated, and the derating range is close to 50%. 

2. Install a hot air curtain inside the LED display screen: a closed channel is built inside the large screen, and a hot air axial flow is installed at the rear. The working state of hot air axial flow is realized by the temperature control system. When the temperature is lower than the set minimum ambient temperature, the hot air blower heats up, the screen body temperature rises, and then the screen body is turned on. When the temperature reaches the set temperature, the temperature control system will cut off the AC power supply to the hot air blower.

3. The outdoor LED electronic display screen is in the open environment for a long time, so it is required that the PCB circuit board, power supply, solder joint, etc. can resist high and low temperatures, waterproof fog, and corrosion. Our company carries out "three proofing" treatment for PCB circuit board, components, solder joints, etc. in an outdoor electronic display screen system. The three proofing paint for the circuit board is a kind of paint with a special formula, which is used to protect the circuit board and its related equipment from environmental erosion, so as to improve and extend their service life and ensure the safety and reliability of use.

The three proofing paint is applied on the surface of the circuit board to form a light and flexible film only 25-50 microns thick. It can protect the circuit from damage in the case of chemical substances (such as fuel, coolant, etc.), vibration, moisture, salt spray, humidity and high temperature, low temperature. Under these conditions, the circuit board may be corroded, mold growth, short circuit, etc., resulting in the failure of the circuit without three anti paint. Our company believes that for the system with long service life, poor service environment and a large number of components, in order to ensure the use reliability of the display screen, it is necessary to carry out strict process control on the Three Preventions of the display screen and adopt the "invasion prevention" process.

In addition, the current-carrying welding technology can eliminate the damage of rosin left in the manual solder to the three proofs, and achieve the true "three proofs" process.

4. Use a low-temperature resistant sheet metal box. In some areas, the temperature often reaches more than minus 30 degrees or even lower. At this temperature, the box of the display screen shrinks because of the principle of thermal expansion and cold contraction, which will cause the gap between the box and the box to become larger, and even cause the same line of light tubes not in the same straight line, which makes the whole screen form a large mosaic phenomenon.

A high-quality steel plate is used for manufacturing, and the whole box body is treated by a hot-dip galvanizing process. During the processing of the box body, the metal surface is cleaned and sandblasted to remove rust; the surface is oxidized and galvanized to prevent oxidation and corrosion; the surface is baked with paint or sprayed with acid-proof grease to effectively prevent the invasion of acid rain mist Erosion.

The influence of temperature on LED display involves many key points. You can refer to our article to reduce the impact of temperature or tell us your project requirements. We will make a complete plan according to your requirements to save your time and energy.