作者：Blade

How to improve CRI of LEDs? (2)

In the previous section, we discussed about the impact of temperature on fluorescent powder. With the increase of temperature, activities of fluorescent powder will decrease. At the same time, temperature will also affect the wavelength of light. Feature below illustrates the relation between temperature and the wavelength. We can see that with the increase of temperature, the wavelength of light emitted though fluorescent powder will red shift. In other words, CRI for LEDs of led lights will be improved (more red rays). It is contradictory to the previous statement: CRI for LEDs will decrease as temperature increases. As a matter of fact, the red shift of fluorescent powder is negligible compare with the degeneration of fluorescent powder. Overall, when temperature drops the CRI for LEDs is actually decreases.

 

In the previous section, we discussed about the impact of temperature on fluorescent powder. With the increase of temperature, activities of fluorescent powder will decrease.

 

According to above analysis, there are three solutions: reduce PN junction temperatures; improve the adaptability of fluorescent powder in high temperatures; use color compensation technology (use red led street light or amber LEDs to compensate the CRI for LEDs);

 

The most effective solution in reducing PN junction temperatures is to design new LED packaging methods with better heat radiating performances. This is one of our development directions that can have Chinese LED industry to make significant progress in intellectual property in the near future. Since LED is a type of low-voltage electronic products, there are not many strict requirements on electrical safety. Thus a lot of heat radiating materials can be used as LED bases. But Chinese LED flood lights  manufacturers have not taken enough research on this part, leading to some foreign intellectual property disputes. Improving the adaptability of fluorescent powder in high temperatures is main research area in international LED technology. Chinese current technique in this respect is relatively weak and cannot break through this bottleneck in the short term. The color compensation technique can improve CRI for LEDs though making up the deficient colors. Theoretically, this solution is feasible. But in real life, there are many restrictions in color mixing technique, with no practical value.

 

Except for the above three solutions, scientists are trying hard to find other methods which can improve the degeneration of fluorescent powder. CRI problem is the main obstacle for LED lamps to replace traditional lamps completely. It is significant to improve CRI for LEDs.

How to improve CRI of LEDs? (1)

With the development of LED products technique, LED lamps have been widely accepted all over the world. In lighting industry, color rendering index (CRI) is an important parameters. Most lighting standards have strict requests for CRI of LEDs. Currently, the immature LED CRI technique obstructs white LED lamps to be the mainstream in the lighting market.

With the development of LED technique, LED lamps have been widely accepted all over the world. In lighting industry, color rendering index (CRI) is an important parameters.

Natural light is a kind of polychromatic light (a continuous distribution in light spectrum). LED white light is closed to natural light (has a wide continuous distribution in spectrum), laying a theoretical foundation for its color rendering capacity. The currently used white LED Lights chips are blue-ray LEDs coated with fluorescent powder. This technique was invented by Nichia Corp, an imitation of the traditional design concept and fluorescent lamps. However, this technique has innate defects: lack of blue-green rays and red rays and too much blue rays and yellow rays. This gives birth to a distorted CIR for LEDs. For some color, like blue and yellow, white LED rays will “exaggerate” them, making objects with these color look brighter than normal. On the other hand, for some red-colored objects, like apple, meat, white LED Tubes rays will make them look dimmer. These are actually distortions. Designers are striving to improve this white-ray LED technique to have a more real natural light.

 

Theoretically, white rays generated though blue-ray LED Street Light chips combined with fluorescent powder are really closed to natural light. But practice is different from theory. This difference is mainly caused by heat. Heat can impact an obvious effect on fluorescent powder. As we all know, high power LEDs will continuously generate heat during the work, meanwhile cooling sections will radiation this heat constantly. And equilibrium happens when LED high bay lamps work in stable situations. The higher the final temperature, the great the influence on fluorescent powder. Feature below illustrates the relation between light intensities and temperatures. Clearly, light intensity will drop with the increase of temperature. In other words, the light emitting capacity of fluorescent powder drops as temperature increases. The best working temperature for fluorescent powder is around 40 oC. When temperature reaches up to 120 oC, fluorescent powder will lose its capacity completely, which means there will no light sent out by LED lamps.

Light attenuation of white LED lamps (4)

Packaging technique:

In the process of package, every step may cause an effect on the performance of LED street light chips. In which bonders and bonding wires (empty solders) are most likely to raise resistances and thermal resistances. If bonders are too tick, or with air bubble, impurities, virtual sticky in them, the resistance and heat resistance also will be increased. However, since the degeneration of fluorescent powder is too obvious. The influence from this kind of packaging defects can be ignored.

 

In the process of package, every step may cause an effect on the performance of LED chips. In which bonders and bonding wires (empty solders) are most likely to raise resistances and thermal resistances.

 

Light attenuation caused by misuses:

  1. Improper power suppliers. This situation may happen when users are not familiar with electric parameters of white LED lamps. Improper power suppliers will cause LED chips working outside the ASO, and consequently light attenuation. Surrounding temperature is measured when LED chips are working in stable conditions. For example, a piece of LED high bay lamp has been installed in the middle of a room, wait until it is in the stable condition, measure the internal temperature of the lamp (near LED chips) rather than the room temperature. If the surrounding temperature exceeds a threshold, lamp will be degenerated or even damaged.
  2. Insufficient cooling methods: the radiation of heat requires enough area for contact surfaces. Some people prefer to add copper blocks on PCBs or aluminum plates, which is meaningless. It cannot solve the heat problem but raise the cost and heavy of products. Most heat generated by PCBs or aluminum plates will be gathered in these copper blocks. When they reach the peak of their thermal capacity, no more heat will be absorbed. Using thermal capacities of materials to help radiate heat cannot solve this problem thoroughly. It can only cool the device for a short time. Designers should not choose auxiliary cooling materials according to their thermal capacities but their specific heat capacities. Water has powerful specific heat capacities, which is widely used cooling materials. The specific heat capacity is only half of aluminum. However, neither copper blocks nor aluminum blocks are unsuitable for white LED lamps. The best way is natural cooling. Natural cooling relies on the area of radiators’ surface not the volume. If these heat generated by white LED lamps can be radiated in time, the light attenuation phenomenon will be slowed down effectively.

High power LED street light will continue rapid growth

“2012, the most promising commercial lighting and road lighting”commercial lighting and road lighting with the semiconductor lighting technology has become more sophisticated and with the publishing from central to local government support policies,  LED lighting has become in 2012 a number of manufacturers to compete in the battlefield road lighting.

2012, is bound to be a year full of opportunities and challenges of China’s LED industry, how to seize the opportunity to seek progress, the pursuit of sustainable development in the longer seems particularly necessary.  Although high power led street light industry is optimistic, yet how to seperate should depends on the company’s core technology and competitive strength.

For the LED road lights, the national brand is not much, mostly regional brands. Therefore, there are still some room for development of related business. One industry expert said in an interview with reporters, “LED lighting is still in the initial penetration stage,  pre-marketing and consumer’s feedback form a significant impact on product quality and assurance, which is the core foundation fo the enterprise survival and development.

“LED industry is facing new opportunities and challenges, the opportunities are obvious, the challenge is to challenge the vast majority of the country, which is no core technology and core competitiveness in the fierce market. It is bound to be eliminated. JiangsuYangzi Electrical and Mechanical technology Co., Ltd.Technical Director said, the whole lamp 90lm / W LED lamps of the performance have been beyond other fixtures, and are continuous improving, which will inevitably become the mainstream in the near future. Of course, the current phase of the product is not perfect, such as the standard interface, the LED  heat sink material consumption and other issues to be resolved.

high power led street light standards develops lags far behind the development of industry and product. Market LED lights, visible appearance of the product, are designed various, poor interchangeability, maintenance difficulties, which have become constraints LED road lighting R & D and manufacturing. The industry also called on the relevant authorities to develop a refinement to quantify the operational norms or standards as soon as possible. 2012, LED road lighting is consistent with optimistic. High power led street light will play a more important role in the renovation and construction of urban road lighting.

Who is in charge for Mainland China led lighting product standard

● the local industry standards stifle the vitality of the current LED Street Light market:

First, Reginal local standards. The standard will bring local color more or less, which can not meet national and worldwide development of the industry needs. It shackles of foreign enterprises to enter the local market competitiveness, and easily lead to local protectionism.

Second, The scientific nature of the local standards. Subject to the constraints of technology and local level of industrial development, the gold content of the proposed standard, and developers can not match the rapid development likely to cause the shackles of technology development.

Third, the led lighting product standard developed by the enterprise is unreliable.  Present in many areas of the LED High Bay industry standard is by enterprises organizations of their own making. Some companies, itself, with production standards are different to reach. Such enterprises to develop the industry standard for a bit?

The opened LED industry standard, although it is conducive to the development of the industry side, yet if it also can not reach to the national level, authoritative and scientific standard is difficult to guarantee. Because led lighting product standard itself have mandatory color, there is no objective and fair platform, easy to damage the development of the industry.

● The true sense of introduction of industry standards is imminent:

There have been frequent accident caused by the LED products. A hotel in Hong Kong recently occur the fire accidents caused by the outdoor LED display. Today it may be the LED display to cause the accident. Tomorrow may be the LED lighting to cause the accident. If there is no industry standard, who are responsible for the safety of the lives and property of consumers.

No related industries label is not benecial to healthy development of enterprises. Study is a required couse of the LED manufacturing. But if there is none of the relevant industry standards, what should be the guidance to corporate R&D. Enterprises will explore whether the results of the final outputs is adapt to the market or not, which is unknown.

Industry label can calm down price wars at some extend. With industry standards to spur business development and product quality control, the led lighting product market will not look the same product but the price different between mystery phenomenon. The strength of the small workshop enterprise is no longer possible to blind pursuit of price, profit and confuse the market.

Light attenuation of white LED lamps (3)

There are three types of bases of SMD LED Street Light chips: glass fiber, plastic, ceramic material. When in packaging, each LED chip will be fixed directly in a copper sheet, for that copper has a very high thermal conductivity. However, the volume of copper sheets is so small that heat will be radiated into external PCBs though a very short path. Experiments prove that SMD LED Street Lights chips with good cooling designs have a much longer life than plug-in LED chips. Similar low power LED chips but different packaging (low power supports/high power bases) will have different working lives. For example, 9 10 x 12 mil2 LED chips fixed in parallel on base surface, under a total working current of 350 mA. After 7600 hours’ constant work, the light attenuation is about 23%. In accordance with this trend, the estimated working life will be 18000 hours. High power packaging chips have surface current density (0.324 mA/mil) twice as much as low power packaging chips (0.167 mA/mil), but has a much longer life than them (almost 9 times), as a result of using materials with higher thermal conductivities and bases with larger area. By doing so, heat can be transmitted not only in radial but also in lateral.

 

There are three types of bases of SMD LED chips: glass fiber, plastic, ceramic material. When in packaging, each LED chip will be fixed directly in a copper sheet, for that copper has a very high thermal conductivity.

 

Other materials used in package:

Heat is the main cause of the light attenuation of white LED lamps. Thus every material related to heat radiation should be taken into account. In previous section, we discussed the LED base problem. Now let us talk about other materials used in packaging process: solid crystal glues, mix powder glues, sealants. Tests results indicate that the life of white LED lamps using silver glues is longer than using epoxy resins, but initial luminous flux is lower by 1/3. Using epoxy resins as mixed glue has a shorter working life than using silica glues, but initial luminous flux is increase by 25%. The most commonly used sealants are epoxy resins and silica glues. As a matter of fact, these two types of materials have very weak heat radiating capabilities. The thermal conductivity of iron is 230 times as much as that of epoxy resins and 150 times as much as that of silica glues. In addition to their thick, they are somehow with no capability of heat radiation.

LED lighting industrial,M & A, should not blindly buy the dips

After the outbreak of the debt crisis in European countries, most Europe welcomed Chinese enterprises to invest, which provides an excellent overseas opportunities for Chinese LED lighting products enterprise. Based on this, in 2011, the acquisitions are waving and surging of the Chinese led lighting industrial, blowing a whirlwind. When entering 2012, M & A momentum is more violent, a lot of acquisitions are world-class enterprise. Mergers and acquisitions wave of the lighting companies will undoubtedly affect the pattern of the lighting industry in China and the whole world lighting industry. But at the same time, we must remind China lighitng enterprises who invest and acquisite in foreign enterprises should have purpose and target, not blindly buy the dips.

LED overseas acquisition of the road just getting started

When the path of the global economic integration gradually clear, the LED Street Light companies of overseas mergers and acquisitions will be mature and normal, which is inevitable outcome of led lighting industrial. But the worlds economic and development is unstable, the business rules vary widely. If Chine lighting enterprises go at the situation, it is not only faced with rare opportunities, but also facing the challenges of security and other risks. If say the early overseas M & A also belong to the stage of trial and error, then today, a fter accumulation of experience, more peace of mind will be needed. While starting from the rational acquisition, risk prevention point of view, not only the enterprise need to clear the way and significance, but also we hope that government departments who manage large amounts of resouces provide more policy interpretation and support. In a complex political and turbulence, to let China led lighting industrial quickly realize the transformation and upgrading, to flex its muscles on the international market. Of course, the lighting companies in China’s oversea M&A road is just starting its way, the future large and medium-sized enterprises are likely facing the choise of overseas acquisitions. Hundred percent lighting chairman Bo Tao introduced, the next hundred percent lighting acquisition is unclear, according to LED Flood Lights market changes, and combined with its own development to examine the need for the acquisition and how to acquire.

The continuing reason for LED lamp market dilemma?

Third Question: the relevant state LED bidding policy resulted in the unfair competition of the market

2012,  the central project related to the three ministries jointly bidding for the financial subsidy of the national LED Lights, and the “annual output capacity of 200,000 threshold” immediately will be the vast majority aspire struggling to forge ahead in the field of emerging LED companies refused to of the door.

How? LED lamp market as an emerging industry, the market is still in the immature stages and industry standards are not really established. The market capacity is so less, and the real customer goals are not effectively formed. In addition, the ability of the market to digest the LED is unsatisfactory. On earch, how many companies real have the production capacity of annual output of 200,000 LED downlights? As a result, It is convenient for the traditional lighting companies, and disolate the new LED enterprises and companies? The traditional lighting of the successful enterprises (containing malicious competition subjective awareness of LED High Bay enterprises) enjoyed the financial subsidy by the state taxpayers. So letting the new LED lamp market strangled in the new cradle, it is fair, equitable and public?

Concession speak the words, even if the successful corporate annual production capacity to 200,000, and in line with the requirements of the bidding, in line with the requirements of the bidding, how much the ability of its companies sold to the market? So, that consistent with the so-called “successful request” LED business (in cluding the traditional LED lighting enterprises), who apply for state financial subsidies can assure not accepting any money within the real guarantee. That sold abroad products had been counted? Is it not the tax dollars fo our people directly benefit the foreigners? It is strange that the foreign people is not happy.

Looking back at the main body of the international social market economy, government in each country are in the role of management and service functions. If it disturb a market economy, the use of financial subsidies might break the normal balance of the development of LED lamp market.

As lighting industry start late of its field, the real force in the field of LED Street Light enterprises who may also be looking at the share of financial subsidies is inaccessible. Each of us must put ourselves in a right position. In modern society, each of us should curtain when it staged of history. In order to facilitate the emerging forces to stand on the stage at the moment.

Light attenuation of white LED lamps (2)

Currents higher than the normal working current will speed up the light attenuating process, dramatically reducing the working life of white LED Lights. There are several other facts can prove that fluorescent powder’s degeneration is the main factor fir the short life of white LED lamps: 1. Normally, we will find that after aging tests, most white-ray LEDs send out a kind of blue-white rays instead of white rays, indicating the degeneration of fluorescent powder; 2. Some people tested the performance of blue-ray LED chips and found that although the capability of the entire LED lamp has dropped more than 30%, the degeneration of LED chips is only a few percent. This shows that most degeneration is from fluorescent powder. 3. Same chips, high power package has a much longer life than low power package. (will be discussed more in details in next section)

 

Currents higher than the normal working current will speed up the light attenuating process, dramatically reducing the working life of white LEDs.

 

Overall, under the influence of temperatures, the degeneration of fluorescent powder is inevitable. The higher the temperature, the fast the degeneration.

 

The degeneration of blue-ray LEDs:

Among LED chips, blue-ray LEDs have the shortest working life. The average life of low power plug-in blue-ray LEDs under normal working current (20mA) is around 7000-10000 hours. Low power plug-in red-ray LEDs working under 50mA current, they will suffer no light attenuation even after 8000 hours. Besides, the average life of yellow-ray LEDs and green-rays LED Street Light are longer than 10000 hours. Thus this congenital defect of blue-ray LED chips is another main factor for the short lives of white LED lamps. The internal materials of LED chips cannot be changed, but scientists still can apply themselves on finding better materials for external parts of LED chips.

 

Materials made up LED bases have bad thermal conductivities:

Usually, low power plug-in LEDs will be fixed on based made up by iron. From the view of heat radiation, iron has a very low thermal conductivity. Meanwhile, cross areas of supporters are usually small, which cannot radiate heat in time. Materials and constructions of LED bases will cause the weak heat radiation behavior of low power plug-in LED lamps. Copper has much better heat radiating capability than iron. In consideration of its high price, LED manufacturers have to reduce the cost at the cost of performances and lives of their products.

why led lighting is still on the muddy road?

2012 will take off years of LED lighting, and Why it says that why led lighting is still on the muddy road?? It is estimated that 2012 LED lighting output used in architectural doubled than last year, which grow to  $ 684 million. Fluorescent lighting market from this year, the neon-oriented market, and slowly transferred toward the direction of LED lighting. Admittedly, the future LED lights is expected to completely replace the neon signs. And then to become the protagonist of the architectural lighting market.

Although LED lighting as a new generation of lighting products, it is a major representative of the product as a milestone in the lighting industry, and excellent in all aspects of LED lighting. But right now, the heavy dusk of LED lighting market, when to poke cloudsd and see the sky, which is worth exploring. Most Chinese enterprises walk in the midstream and downstream industry chain, and only a small part of Chinese enterprises is difficult to survive. Technical problem is the primary obstacle to impede Chinese companies.

Since Steate and local governments to support this emerging LED industry efforts to the enterprise, and introduction of various policies and preferential measures. So, it set off a place to get the building wave of large LED production base. why led lighting keeps the same? Because the low threshold of downstream technology, which easily entered into the LED industry-the most appropriate incision. The inevitable result of such large-scale investment in upstream and downstream industrychain is redundant construction and waste of resources, and even generate excess capacity and foam.

Because various parts of LED street light manufacturers emerged, more than 500Taiwan-funded lighting companies in the Guangdong region alone. A large number of enterprises are concentrated in the top of the upstream and downstream industry chain, thus leading  to a competition in the downstream industry chain reminder serious, and less profits. Enterprises have to low price of the products in order to seize the market, which led to one confusing reasons of the LED stage of the domestic market.

LED insider think that why led lighting have no market? the high price of LED lighting products are only argument, in fact, the real reason is that how many people know LED? If only to be told or understand the products, how to get consumers to buy? Moreover, the price of LED products is relatively higher, Market come and go grumbling grow up!