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Why is the volume of LED lamps larger than traditional lamps?

July 30, 2020

Generally speaking, why is the volume of LED lamps larger than traditional lamps?

Mainly because of LED cooling technology. Heat dissipation is a major factor affecting the lighting intensity of LED lamps. The heat sink can solve the heat dissipation problem of low-illuminance LED lamps. A heat sink cannot solve the heat dissipation problem of 75W or 100W LED lamps. In order to achieve the ideal lighting intensity, active cooling technology must be used to resolve the heat released by the LED lighting components. Some active cooling solutions such as fans have less lifespan than LED lamps. In order to provide a practical active cooling solution for high-brightness LED lamps, the heat dissipation technology must be low energy consumption; and suitable for small lamps; its life span should be similar to or higher than the lamp source.

Generally speaking, according to the way the heat is taken away from the radiator, the radiator can be divided into active heat dissipation and passive heat dissipation.

Passive heat dissipation means that the heat of the heat source LED light source is naturally dissipated into the air through the heat sink. The heat dissipation effect is proportional to the size of the heat sink, but because the heat is naturally dissipated, the effect is of course greatly reduced. It is often used in those who do not require space. For example, some popular motherboards also adopt passive cooling on the north bridge. Most of them adopt active cooling. Active cooling is forced by cooling devices such as fans. Taking away the heat emitted by the heat sink is characterized by high heat dissipation efficiency and small size of the equipment.

Active heat dissipation, subdivided from the heat dissipation method, can be divided into air cooling, liquid cooling, heat pipe cooling, semiconductor cooling, chemical cooling and so on. Air cooling is the most common heat dissipation method, and it is also a cheaper method in comparison. Air cooling is essentially the use of a fan to take away the heat absorbed by the radiator. It has the advantages of relatively low price and convenient installation. However, it is highly dependent on the environment. For example, the heat dissipation performance will be greatly affected when the temperature rises and overclocking.

Currently, the heat dissipation of LED lamps mainly has the following methods:

1. Liquid cooling

Liquid cooling heat dissipation is the forced circulation of liquid under the drive of a pump to take away the heat of the radiator. Compared with air cooling, it has the advantages of quietness, stable cooling, and less dependence on the environment. The price of liquid cooling is relatively high, and installation is relatively troublesome. At the same time, try to install in accordance with the instructions in the manual to get the best heat dissipation effect. For cost and ease of use considerations, liquid-cooled heat dissipation usually uses water as the heat transfer liquid, so liquid-cooled radiators are often called water-cooled radiators.

2. Heat pipe

The heat pipe is a kind of heat transfer element. It makes full use of the principle of heat conduction and the fast heat transfer properties of the refrigerant. It transfers heat through the evaporation and condensation of the liquid in the fully enclosed vacuum tube. It has extremely high thermal conductivity and good isothermal properties. The heat transfer area on both sides of the cold and heat can be changed arbitrarily, heat can be transferred over a long distance, temperature can be controlled, etc., and the heat exchanger composed of heat pipes has high heat transfer efficiency, compact structure, small fluid resistance, etc. advantage. Its thermal conductivity has far exceeded that of any known metal.

3. Semiconductor refrigeration

Semiconductor refrigeration is to use a special kind of semiconductor refrigeration chip to produce temperature difference when energized. As long as the heat of the high temperature end can be effectively dissipated, the low temperature end will be continuously cooled. A temperature difference is generated on each semiconductor particle, and a refrigeration sheet is formed by connecting dozens of such particles in series, thereby forming a temperature difference on the two surfaces of the refrigeration sheet. Using this temperature difference phenomenon, combined with air cooling/water cooling to cool the high-temperature end, an excellent heat dissipation effect can be obtained. Semiconductor refrigeration has the advantages of low cooling temperature and high reliability. The cold surface temperature can reach below minus 10℃, but the cost is too high, and it may cause short circuits due to the low temperature, and the current semiconductor refrigeration technology is not mature and insufficient practical.

4. Chemical refrigeration

The so-called chemical refrigeration is to use some ultra-low temperature chemical substances, and use them to absorb a large amount of heat when they melt to reduce the temperature. In this regard, the use of dry ice and liquid nitrogen is more common. For example, using dry ice can reduce the temperature to below minus 20°C, and some more'perverted' players use liquid nitrogen to lower the CPU temperature below minus 100°C (in theory). Of course, due to the high price and the short duration, this The method is more common in the laboratory or extreme overclocking enthusiasts.

The choice of heat dissipation material. Generally speaking, ordinary air-cooled radiators naturally choose metal as the material of the radiator. For the selected material, it is hoped that it has both high specific heat and high thermal conductivity. Silver and copper are the best thermal conductivity materials, followed by gold and aluminum. But gold and silver are too expensive, so the current heat sink is mainly made of aluminum and copper. In comparison, both copper and aluminum alloy have their own advantages and disadvantages: copper has good thermal conductivity, but it is more expensive, difficult to process, heavy, and copper radiators have small heat capacity and are easy to oxidize . On the other hand, pure aluminum is too soft to be used directly. The aluminum alloy used can provide sufficient hardness. The advantages of aluminum alloy are low price and light weight, but the thermal conductivity is much worse than copper. Therefore, in the history of the development of radiators, products with the following materials have also appeared:

1. Pure aluminum radiator

Pure aluminum radiator is the most common radiator in the early days. Its manufacturing process is simple and the cost is low. So far, pure aluminum radiator still occupies a considerable part of the market. In order to increase the heat dissipation area of ​​its fins, the most commonly used processing method for pure aluminum radiators is aluminum extrusion technology. The main indicators for evaluating a pure aluminum radiator are the thickness of the radiator base and the Pin-Fin ratio. Pin refers to the height of the fin of the heat sink, and Fin refers to the distance between two adjacent fins. The Pin-Fin ratio is the height of Pin (excluding the thickness of the base) divided by Fin. The larger the Pin-Fin ratio means the larger the effective heat dissipation area of ​​the heat sink, and the more advanced the aluminum extrusion technology.

2. Pure copper radiator

The thermal conductivity of copper is 1.69 times that of aluminum, so under the same other conditions, the pure copper radiator can quickly remove heat from the heat source. However, the texture of copper is a problem. Many advertised as "pure copper radiators" are not actually 100% copper. In the list of copper, those with a copper content of more than 99% are called acid-free copper, and the next grade of copper is red copper with a copper content of less than 85%. The copper content of most pure copper radiators on the market is somewhere in between. The copper content of some inferior pure copper radiators is even less than 85%. Although the cost is very low, its thermal conductivity is greatly reduced, which affects the heat dissipation. In addition, copper also has obvious shortcomings, such as high cost, difficult processing, and large heat sink quality, which hinders the application of all-copper heat sinks. The hardness of red copper is not as good as aluminum alloy AL6063, and some mechanical processing (such as slitting, etc.) is not as good as aluminum; the melting point of copper is much higher than that of aluminum, which is not conducive to extrusion and other problems.

3. Copper and aluminum bonding technology

After considering the respective shortcomings of copper and aluminum, some high-end radiators in the current market often use a copper-aluminum combination manufacturing process. These heat sinks usually use copper metal bases, and the heat sink fins use aluminum alloy. Of course, In addition to the copper bottom, there are also methods such as using copper pillars for the heat sink, which are also the same principle. With high thermal conductivity, the copper bottom surface can quickly absorb the heat released by the CPU; aluminum fins can be made into shapes that are most conducive to heat dissipation with the help of complex processing methods, and provide larger heat storage space and release quickly. A balance point found in all aspects.

To improve the luminous efficiency and service life of LEDs, solving the heat dissipation problem of LED products is one of the most important issues at this stage. The LED industry has extremely strict requirements on the alignment accuracy of the heat dissipation substrate itself, and it needs to have high heat dissipation and small size. The characteristics of size and adhesion of metal lines are good. Therefore, the use of yellow light lithography to make thin-film ceramic heat dissipation substrates will become one of the important catalysts to promote the continuous improvement of LEDs to high power.

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