日期：2012年12月25日

How to improve the luminous efficiency of white-ray SMD LEDs

In the past, in order to improve the luminous efficiency of white-ray SMD LEDs, engineers tried to develop large sized LED chips to achieve their goals. However, in fact, if white-ray LED chips continue to work under power supply higher than 1W, their luminous efficiency will reduce by 20%-30% on the contrary. In other words, if white-ray LEDs intend to have brightness several times larger than traditional LED chips and better voltage-current characteristic than fluorescent tubes, they need to overcome following shortages: temperature control, ensure the lifetime of LED chips, improve luminous efficiency and equalize luminescent characteristics.

 

How to improve the luminous efficiency of white-ray SMD LEDs

 

The most effective method to control temperature rising is reducing the thermal resistance of LED chips during the package process. The commonly used method to extend the lifetime of white-ray SMD LEDs is applying small sized LED chips. For the equalization of luminescent characteristics, the most effective way is still optimize the package of white-ray LEDs. More specific methods are still in developing now.

 

The core solution is improving the cooling problem of package. Increasing power will result in drastically reduction of thermal resistance of LED chips to less than 10K/W. In order to solve this problem, many foreign G24 LED makers developed white-ray SMD LEDs with high heat-durability. In fact, high-powered LEDs will generate much more heat (more than 10 times) than low-powered LED chips. High working temperature will speed up the process of light attenuation. But the junction temperature of LED chips can exceed the allowable value and exert very limited influence on the light attenuation. After all, LED engineers started to notice that and spent more energy and money on the package cooling.

 

Using suitable materials can improve the service life of LED chips. For example, siliceous and ceramic packaging materials can increase the service life of LEDs by 10%. The spectrum of white-ray LED chips contains light with wavelength below 450nm, which is also known as short wavelength light. Traditional epoxy encapsulation materials will be easily destroyed by this kind of rays. Plus that the large amount of luminance of high-powered LED chips will also accelerate the deterioration of packaging materials. According to related testing reports, after 10,000-hour constant lighting, the brightness of high-powered white-ray LEDs is reduced by more than 50%, cannot meet the basic requirement of long lifetime of light sources.

Influences of SMD LED beads to LED screens

For full color LED screens, SMD LED beads can be said the most important part. The quality of LED chips plays a key role in determining the quality of LED displays.

 

For full color LED screens, SMD LED beads can be said the most important part. The quality of LED chips plays a key role in determining the quality of LED displays.

 

LED beads are the mostly used components in full color LED screens, there are probably thousands or even tens of thousands of SMD LED beads on every square meter of the lighting board used in LED displays. In addition, SMD LEDs also directly determine the performance, color saturation and sharpness of LED screens.

 

The main performance figure of SMD LED beads mainly determines:

1)       The brightness of LED screens: the brighter the LED chips/the greater the margin of current, the better the quality of LED screens. This type of screens has higher reliability and can save more electricity. LED chips have different angles. With the same brightness, the narrow the angle, the brighter the LED beads, but the visual angle will become narrow all together. Normally, manufacturers choose LED beads with beam angle of 100 degrees to 110 degrees to meet the requirements of visual angle and brightness of LED screens.

 

2)       The failure rate of LED full-color display: G24 LED display is composed by tens/hundreds of thousands of red/green/blue SMD LED beads. The failure rate of LED beads with good quality will be no more than the ten-thousandth after a 72-hour ageing test.

 

3)       The attenuation characteristics of LED full-color display: definitely, the brightness of LED beads will reduce over time, which is also known as light attenuation. The speed of light attenuation is mainly determined by the quality of LED chips, assisted materials and packaging process. Normally, under 20mA driving current, at room temperature, after 1000-hour aging test, the light attenuation of red chips should be less than 7%, and the light attenuation of greed/blue chips should be less than 10%. The attenuation rate of red/green/blue chips has great influence on the white balance of full-color LED screens, and consequently their fidelity.

 

4)       Anti-static ability of LED display: since SMD LED chips are semiconductor devices, they are very sensitive to static electricity, easily leading to static electricity failures. So the anti-static ability is critical to the life of LED displays. Generally speaking, the threshold voltage of body static mode tests of LED beads should not be less than 2000V.

New cooling mode for small and medium power LED lights – vertical heat dissipation mode

Compared with traditional light technologies, LED solid source has high luminous efficiency, pure color, low power consumption, long service life, high reliability, flexible in applications, zero contamination. Currently LED light technology has been widely used in road lighting, residential lighting, vehicle lighting and outdoor landscape lighting areas. Good heat dissipation capability is a basic guarantee for the performance and reliability of LED lamps. Working temperature has significant influences on LEDs’ performances, including changes of color temperature, red shift of wavelength, decline of efficiency, etc. Therefore, good LED lighting devices must be equipped with good heat control systems. In this article, we will discuss about advantages of the vertical heat dissipation mode in small and medium power LED lights. Compared with traditional cooling modes, LED lamps, especially small and medium power LED lights using vertical heat dissipation modes have features of high brightness, fast cooling, low light attenuation, low production cost, reliable. Vertical heat dissipation mode is, can be said, a developing trend of LED lighting industry.

 

New cooling mode for small and medium power LED lights – vertical heat dissipation mode

 

This article will compare new vertical cooling mode with traditional horizontal cooling mode through comparisons between commonly used 3014 LED and 3528 LED respectively. 3528 LED chips realize cooling effects through electrodes weld legs at both ends of electrodes. Thus they use horizontal cooling mode. 3014 G24 LED chips conduct heat through metal substrates, which is vertical cooling method.

 

In order to calculate the thermal resistance more accurately, we firstly set the temperature parameter of substrates as 60℃, chip power as 0.06W, the thickness of solid crystal glue is KER-3200-TI is 0.01mm, the driving current is 20mA. According to the analysis of ANASYS (a type of finite element analysis simulation software), in the same working condition: set as above, the working temperature of vertical cooling mode is higher. This is mainly because that the volume and cooling area of 3014 is much smaller than that of 3528, in which the heat is more concentrated. But the temperature difference of vertical cooling mode is smaller, resistance of which is far lower than LED chips using horizontal cooling method. In other words, the cooling effect of vertical cooling mode is more advance than that of horizontal cooling mode.

 

 

General analysis of traditional LED power supplies

Because of the incomparable features of LED lighting fixtures: environmental friendly, long lifetime, high photoelectric efficiency (the average luminous efficiency of white-ray LEDs has reached up to 100lm/W), LED lighting technology received rapid development in various industries. Theoretically, the average lifetime of LED chips is around 100,000 hours. But this value has never been approved by practical applications. Some LED lamp designers is lack of knowledge of LED power supplies. In order to reduce production cost, they tended to choose cheap LED drivers, without knowing that drivers are one the most important parts of LED lighting devices.

 

Because of the incomparable features of LED lighting fixtures: environmental friendly, long lifetime,

 

LED drivers, also known as LED power supplies, are a type of converter output special voltage and current. The normal input modes of LED drivers include high-voltage low-frequency AC, low-voltage DC, high-voltage DC and low-voltage high-frequency AC (such as electronic transformer) and so on. The output of LED power supplies is normally constant current sources, which can change voltage with the variations of LED internal forward voltage drop. Core components of LED drivers include: switch controllers, inductors, switching components (MOSFET), feedback resistors, input filter components, output filter pieces. According to the requirements of different occasions, output over-voltage protection circuit, input under-voltage protection circuit, G24 LED open-circuit protection, over-current protection circuit are also needed in some cases.

 

Key sections of making a good LED lighting product are cooling sections, drivers and light sources.  The heat dissipation is particular important. And the cooling effect is a direct impact on the quality and the lifetime lighting products. The lifetime of LED drivers, the stability of output current/voltage also have significant impacts on the service life of the entire lamp. Light source is the core part of LED lighting fixtures.

 

Because of the particularity of LED manufacturing technologies, different makers (different products from one makers) will produce LED drivers with huge individual differences in current and voltage. Take 1W high-powered white-ray LED chips for example: generally, the forward working voltage of 1W white-ray LEDs is around 3-3.6V. In another word, suppose the internal current flow of one 1W LED white-ray LED is 350mA, voltage across it may 3.1V, 3.2V or 3.5V. When the internal current flow within LEDs reached 350mA, any tiny fluctuations of input voltage will cause huge increase of forward current, and consequently working temperature, which, as we all know, will speed up the light attenuation of LED chips.

 

How to slow down the light attenuation of LED lamps

Working temperature of LED chips is one of major factors that lead to light attenuation of LED lamps. In accordance with the aging test results of single white-ray LED lamps, if the surrounding working temperature is 30 centigrade, then the bracket temperature of single white-ray LED chip will not be more than 45 centigrade. In this condition, the service life of this single LED chip is “ideal”.

 

Working temperature of LED chips is one of major factors that lead to light attenuation of LED lamps.

 

If there are more than 100 white-ray LED chips work together. The distance between them is supposed 11.4mm. Then the bracket temperature of LED chips on the edge may not surpass 45 centigrade, but the temperature of LED chips in the center will be more than 65 centigrade. Theoretically, in this situation, LEDs in the center will suffer a much fast light attenuation then LEDs on the edge.

 

As we all know, LED cannot stand the heat. The higher the temperature, the shorter the lifetime of LED chips, vise visa. The ideal working temperature of LED chips is from -5 centigrade to 0 centigrade, which is impossible. So that, after learning the ideal operation parameters, designers and engineers need to strengthen the heat dissipation performance of the entire lighting fixture.

 

Another factor that may cause fast light attenuation of LED lamps is the electronic parameter of LED chips. Working under low input current, white-ray LED chips generate low heat, and consequently low brightness. The driving current of LED solar-related LED lamps is around 5-10mA. LED lamps utilized a large number of LED chips, like more than 500 hundreds, may need higher driving current: 10-15mA or more. The driving current of general lighting applications is around 15-18mA. Very few engineers would like to make the driving current more than 20mA.

 

Corresponding experimental data shows that, under 14mA driving current, without any cooling solutions, the internal working temperature is 71 centigrade, the light attenuation of good quality LED chips is almost aero after 1000-hour constant work, and only 3% after 2000-hour constant work. However, this is the worst working condition that good quality (low light attenuation) white-ray LEDs can endured. Working conditions worse than this will cause huge damages to low light attenuation LED chips, speeding up the light attenuation of LED lamps.

Reasons for LED light attenuation

As new lighting source, LED has a lot of incomparable advantages: energy saving, environmental friendly, long service life, etc.. LED-related lighting fixtures received more and more attentions of consumers and producers. But LED light attenuation is also a big problem for LED manufacturers, which must be solved. Fast light attention impact the service life of LED lamps. Now, engineers faced bottlenecks in this area.

 

As new lighting source, LED has a lot of incomparable advantages: energy saving, environmental friendly, long service life, etc..

 

From current situations, LED light attenuation will become the biggest obstacle for LED lighting devices to enter the market of general lighting applications. What causes the light attenuation of LED lamps? Generally speaking, there are two major reasons:

1)       Quality of LED chips: LED chips with bad quality will speed up the lighting attenuation; production process defects, especially defects in the packaging process will reduce the cooling effect of LED chips. Heat generated by LEDs cannot be conducted outward on time, leading to the continuous temperature increasing in LED chips.

2)       Inappropriate applying conditions: normally, LED lamps use constant current power supplies, but some LEDs may be drove by constant voltage power supplies, which will cause long-term damages to G24 LED chips, speeding up the light attenuation; If the diving current exceeds the rated current, there will be more light attenuation, as well.

 

There are a variety of reasons may lead to LED light attenuation, heat dissipation is the most critical problem. Although many LED manufacturers spent a lot of energy and money on the secondary products (LED modules, LED applications), they still cannot maintain normal working conditions for a long time. The light attenuation of these secondary products is more serious than products with good cooling solutions. LED light attenuation has closed relations with the thermal resistance of LED chips, influences from silver plastics, the cooling effect of substrates, colloids and gold wires.

 

The quality of white-ray LED lamps can be said that a rather important factor for light attenuation. For example, same crystal 14mil white-ray LED chip: if using ordinary epoxy as bottom glue, packaging together with white glue and packaging glue, after 1000-hour constant working in 30 centigrade, the light attenuation is about 70%; if using D-type packaging glue, after 1000-hour constant working in 30 centigrade, the light attenuation is around 45%; if using C-type packaging glue, the light attenuation is only 12%; if using B-type packaging glue, the light attenuation is -3% (brighter than original products); if using A-type packaging glue, the light attenuation is -6% (even better).

Bridgelux promoted a new generation of Vero LED array

Bridgelux is the lead manufacturer of LED lighting technologies and solutions. On 5th of December this year, they promoted a new generation of Vero LED array. This innovation not only simplified the design and manufacturing process of LED chips, but also provided a more flexible lighting solution for designers.

 

Bridgelux is the lead manufacturer of LED lighting technologies and solutions.

 

Vero new generation array package technology is more advanced in terms of design flexibility, ease of use and energy efficiency, and meanwhile provides integrated smart sensors and wireless communication technologies for the future constructions of intelligent control systems and all sorts of application innovations.

 

The Vero LED array has three major innovations: a. as the new generation of LED array, Vero array have higher luminous flux density (20% more than current LED arrays); b. the birth of Vero array can further simplify the packaging process of LED chips, improving production efficiency and reliability of the entire system. Overall, Vero LED array can significantly reduce the inventory of electronic and optical components of G24 LED manufacturers, expand the scope of the input current, and enable designers to take optimizations on production efficiency, cost and output luminance.

 

Vero array provides complete application supports for four LED specifications, and provides suitable output luminance and color temperature to multiple areas, such like retails, catering and tourism, commercial, industrial, residential, outdoor and indoor lighting. The new array products will initially provide approximately 800lm warm white (3000K) light, the maximum output luminance of which were expected to reach up to 20,000lm. These new chips also offer multiple options in CCT and CRI, including Décor array products with CRI up to 97.

 

Vero array products are compatible to many standard divers, providing diverse and flexible choice for LED manufacturers, and meanwhile further reducing the research and developing time of new products, reducing inventories and saving costs. They have significant improvement in general lighting designs, more flexible, surpassing all previous array products of Bridgelux in luminous flux density and current stability. The new Vero array brings about interfaces with higher qualities and also multiple connection options to LED makers. They could use general welding boards or plates without welding links (provided by Molex) to establish links. Vero series combined advanced light sources and innovated linker design options to establish simple and easy-to-integrated solutions for LED manufacturers.

Analysis of LED commercial indoor lighting applications

Compared with traditional light sources, LED lighting technology has many incomparable advantages: more easily integrated, can be intelligent controlled, dimmable, color changeable, flexible in designs. Almost every type of LED lights are dimmable, the corresponding approaches are much simple than that of traditional lamps. Basically, via power amplifiers, LED dimmers can simply realize constant 0-100% dimming function without any flickers. Even more intelligently, by using DMX512 controllers, LED lighting fixtures can dynamically controlled according to the specific requirements of clients, since these DMX512 devices are programmable. This new control technology is rather popular among LED commercial indoor lighting applications. On the other hand, it is very difficult for traditional lamps to realize dynamic changes both in brightness and colors.

 

Compared with traditional light sources, LED lighting technology has many incomparable advantages:

 

Currently, the design of commercial lighting applications takes more considerations on user-friendly contents, like different color options for different environments, different color temperatures to meet the specific of customer’s requirements or simply convey the design concept of designers. Take jewelry counter for example, platinum counter areas usually used 7000-8000K white-ray LED lights, which can fully present the elegant and elitist of them. 3500-3800K warm white G24 LED rays are more suitable for gold products, which can present their magnificence and gorgeous. The small size, narrow beam angle and high luminous efficiency let LED lights become a good replacement of fluorescent tubes in jewelry counter lighting applications. Different business environments, different shopping experiences make practical applications have more and more restrict requirements on lighting designs. LED commercial indoor lighting applications can easily achieve all kinds of effect that merchants wanted, which cannot be realized by traditional lamps.

 

The luminous efficiency of LED commercial indoor lighting applications grows increasingly, they started their seizing in the indoor lighting market. At present, traditional light sources still dominate the commercial indoor lighting area. Energy-saving lamps are cumbersome in size. The entire lamp body occupies a large space, lacking of aesthetic feelings. If worked under unstable AC input voltage, there will be flickers. Light sources and shell of LED down lights followed the integration design, applying creamy white shells, nebulizer covers and embedded lamp bodies. Graceful appearance, even light distribution, even light distribution, not subject to the restrictions of the external voltage variations, consistent luminance, all above advantages make LED commercial indoor lighting applications more competitive in the lighting market.

Advantages and prospects of the development of LED commercial indoor lighting industry

Since the birth of LED lighting devices, they has received high attentions from both engineers/designers and consumers, due to their features of high reliability, easy to control, small size and energy-saving. Electronic indicators are the earliest product of LED lighting technology, followed by signal indicators, like traffic lights. However, at the early stage, the output luminance (brightness) and luminous efficiency of LED lights are relatively low, but their selling prices are ridiculously high, thus for a very long time, LED lighting fixtures were hardly cognized and accepted by ordinary buyers. In the commercial applications, LED lights were only sued as outline decorations of buildings and other non-mainstream lighting applications.

 

Advantages and prospects of the development of LED commercial indoor lighting industry

 

In recent years, with the increase of LED thermal energy conversion efficiency (also known as power efficiency) and brightness, and meanwhile the decline of production costs/selling prices, the market had some new recognition on this new generation light source. In fact, LED has multiple incomparable advantages, like long service life, low power consumption, high output luminance. According to related analysis of the lifetime and power consumption of LED lighting fixtures, LED commercial indoor lighting industry has more potentials and prospects in the commercial indoor lighting market. After 20 years development, the production cost of LED bulbs, LED ceiling lamps, G24 LED down lights and LED bars is obviously lower than the cost of traditional light sources. It is estimated that, in 2012, with the further drop of LED chip product cost and further increase of LED chip technology, the performance advantages of LED lights will be more obvious.

 

Compared with traditional light sources, LEDs have more plastically, which means LED chips provide more creative space to fixture designers. The small size enables them to be used in diverse applications in diverse environments. Take LED down lights for instance, they can be made in a variety of shapes, such like round, square, other irregular shapes, also can be made in panels with thickness of only 9mm. All these designs cannot be used on traditional light sources. Incandescent lights are usually made as bulbs and fluorescent lights are usually made as tubes, all depending on their corresponding technological features.

 

However, the development of each industry must follow some certain laws, including LED commercial indoor lighting industry, from start to development to mature then finally to recession. LED commercial indoor lighting industry is still in the stage of development. How to successfully move forward into mature stage, it is a crucial problem.

 

Importance of the design of LED lamp drivers

LED lamp drivers are also power supplies of LED lamps. Efficiency is the most important parameter for them. LED drivers with relatively low efficiency will greatly impact the energy-saving feature of we LED lighting products. Meanwhile, among all LED lighting applications, the unmatched service life and reliability of LED lamp drivers will affect the reliability of LED lamps, which is also seen as the “short blank” of LED lighting devices. Giving full play to their potential is the key supporting factor.

 

LED lamp drivers are also power supplies of LED lamps.

 

In order to meet requirements of different LED lighting devices (with different input voltage/current and different LED chips), LED semiconductor device companies have developed a variety of new white-ray LED drivers. These drivers can also be used on blue-ray, red-ray and other color LEDs as well as white-ray LEDs. In addition, this kind of driver has features of stable output and programmable output. Thus they could be used as a regulated power supply or a programmable constant current source.

 

LED lamp drivers must ensure that the corresponding G24 LED lamp can maintain a normal working condition. For example, as the load of LED power supplies, dozens or even hundreds LED components need to combined together to form a light-emitting module. How to choose a suitable power supply? What type of connection should be used between drivers and LED components? All these factors directly determine the reliability and service life of LED lighting fixtures.

 

Power supplies provide forward input voltage to LEDs to trigger current flow. The output luminance (brightness) of LED chips is usually determined by the forward current flow. However, the internal current flow should below the rated current of LED lighting devices, otherwise, permanent damages may come out. Therefore, the constant current circuit of LED drivers is the best solution to realize current control currently. In other words, LED lamp drivers are a type of conversion circuit that provided constant current rather than constant voltage.

 

LED technology is relatively mature compared with other LED technologies. In normal conditions, the average lifetime of them can reach up to 100,000 hours. Among all sections of LED lighting fixtures, it is LED divers that have the shortest working life. The average service life of general high-powered LED divers is only 30,000 hours, far less than the lifetime of LED chips. Thus how to improve the lifetime of LED power supplies is a crucial point of LED lighting technology.