How to choose lamp beads for LED car headlights?
Why does the LED Light give out light?
To mention this question, I hesitated for a long time. It is a very professional knowledge point, and if I want to explain it in a popular way, I still find it difficult to replace all of technical terms with common language, but I will do my best.
LED (short for light emitting diode) is not something new and was invented in the 1960s. The electric light we used before is energized through the tungsten wire or other metal wires, and the heat energy will transform into the light energy when its temperature reaches the incandescent point. However, the LED is different (early warning for the impact ahead!!!!!!!). It has unilateral conductivity. When the LED is added with the forward voltage, the holes injected from the P region to the N region and the electrons injected from the N region to the P region combine with the electrons in the N region and the holes in the P region in a few microns near the PN junction, respectively, and the LED produces the spontaneous radiant fluorescence.
Normal to be dumbfounded. In common words, it means that the semiconductor material inside the LED is able to fluoresce after charged with electricity, and how it is stimulated is not what we care about. The advantage is that the LED gives out cold light with higher luminous efficiency, which is unlike the incandescent light, as plenty of electric energy has to be converted into heat energy and is wasted. The incandescent light can only send out 15-24 LPW (luminance unit), and even the halogen light can only reach 90-140 LPW, whilst the LED has the highest luminous efficiency, reaching up to 300 LPW at present. It is not only power-saving but also without heat radiation, so the life span is as high as 100,000 hours.
(LED lights mainly give out red and green rays before the introduction of gallium nitride and now have blue rays as well)
Naturally-grown material is called high quality
In this way, people who have a little bit of physical knowledge can infer that this semiconductor material is very important since the light emitting diode serves as its core. Well, taking the steel for example, good steel can be used for aircraft carriers and gun barrels, while bad steel can only be used for piers. The same goes for semiconductor materials, which are commonly made from indium and gallium compounds with nitrogen, phosphorus, sulphur, arsenic and other elements.
InGaN is one of the core materials as the key to achieve the blue LED with high brightness. Japanese scholar, Shuji Nakamura, won the 2014 Nobel Prize in Physics for his invention of the highly efficient blue LED technology. He initiated the successful growth of InGAN on the sapphire substrate. By the way, such thing is also the key material for photovoltaic electrons, radar and laser weapons… That’s enough of that.
(Great Shuji Nakamura is not professional and learns physics by himself)
InGaN, such a powerful thing, to be honest, can not be produced in China due to less strong production technology. Car fans with sharp eyes may find that the word “grown” was used for expression above. That’s true. At present, the MOCVD (short for Metal-Organic Chemical Vapor Deposition) is the general production method for the preparation of GaN and InGaN. Sapphire is used as the substrate; TMGa and nitrogen are used as the main carrier gas; heating makes them react with each other; they are adsorbed on the sapphire for nucleation and finally become the crystal like a thin film. If you don’t understand, just imagine we’re making sufu. The substrate is tofu; the carrier gas is air, microbes, and salt we add in the tofu can; after a period of time, the tofu gives birth to hyphae, which is similar to InGaN.
So what is good InGaN? The core index of this material is its compatibility with the substrate. Here is another word that is very laborious and torturous to explain. Taking another immature example, we bought a pancake mold and made a pancake on it. In fact, after frying and turning over, the pancake is not the perfectly same of both sides, and there will always be mismatch, bubbling and other phenomena, which can not be 100% avoided. The same is also true for the growth of crystals on the substrate. The higher the crystal compatibility with the substrate, the fewer defects; the lower the compatibility, the more defects.
Surpassing Shuji Nakamura, CREE has unique technique
Although InGaN grown on the sapphire substrate is a great invention, science is still advancing. It is found that the sapphire substrate is good, but there are also shortcomings. Sapphire has low price, good thermal stability and is suitable for making large-sized crystalline film, but its lattice length and linear expansion coefficient are quite different from that of GaN (InGaN is the GaN of high indium content). This is like pitching on the highway of misplaced cement boards, bringing about higher defect density.
At this time, the US CREE stood out. The company employs 6,400 people, but has 4,000 patents! Technology-oriented company is often full of power, adopting a bran-new substrate, that is, SIC, and there are smaller differences between SIC’s lattice constant and linear expansion coefficient with InGaN’s, as opposed to sapphire. Through the exclusive technical patent, CREE achieved the growth of GaN with lower defect density. The defect density of GaN grown on the sapphire is as high as 14.8%, while that of GaN grown on the silicon carbide is only 3.3%.
We’re flying too far in the sky of materials science and it’s time to come back the real world.
Better InGaN, Better Quality.
Lamp bead chip. Our LED light is required to be bright (high photoelectric conversion power), have good light pattern (spotlight) and stability that is not easy to break down (low heat and good heat dissipation). High-quality raw materials ensure higher brightness under lower output power, and the lower the output power, the lower the heat, the more stable the light. There is no doubt that high-quality semiconductor components based on the SIC substrate growth technology play a decisive role.
If you want to choose the LED lamp bead, recommendations are as follows:
There are mainly three kinds of lamp beads in the market. The first one is COB lamp bead, which is not recommended. Here are two reasons: 1) due to structural problems, the general life of COB applied in the car lamp field is poor. At present, it has only about two months of life in the field application. 2) Because of luminous principles, COB has a large area and gives out light roundly, which makes it difficult to gather light.
(You can be happy for 60 days after buying COB lights)
The second one is the lamp bead used by some chip companies in the field of home lighting, such as CREE XHP50. The design of domestic lighting often adopts the circular luminous principle, thus it is also difficult to gather light. That is still not a good choice.
(Household LED lamp bead follows the circular luminous principle and is not suitable for car lights)
The third one is strip lamp bead. You can choose this kind, because it basically simulates the luminous principle of halogen lamp and can realize light gathering. Of course, there are good and bad lamp beads of the same kind, so you’d better choose the lamp beads from some well-known enterprises.
(PAVEDGE Eagle with exclusive use of CREE SiC substrate technology light source)