2013年1月 – 第2页 – LED Lighting Blog

Analysis of the light attenuation of LED roadway lighting applications

Currently, the majority of LED roadway lighting applications face with serious light attenuation. This problem can only be fundamentally solved through the improvement of LED cooling technology. According to recent statistics, China has the highest growth rate in LED roadway lighting applications. It is predict that this dominating will be continued in 2013 in the global market. In 2012, the Chinese Ministry of Science and Technology issued a LED-lighting-related project: “Ten thousand lights in ten cities”. Although this implementation is a economic model that create the market demand via central government policies, but the response is not as good as expected.

Lacking of unified LED standard is not the only reason for the huge gap between the market and policies, serious light attenuation of LED roadway lighting applications is another potential problem for this issue. The former unified standard will be possible programmed in the near future, while light attenuation problem still need to be solved via the improvement of cooling technology.

Temperature is the major element to accelerate the light attenuation. As a type of high-powered LED lighting applications, LED roadway lamps usually work in high temperatures. LED street lights have relatively high working temperatures than ordinary residential lamps. Thus LED manufacturers paid a large amount of energy and money on the development and design of heat dissipation substrates, sinks and other cooling models. After package, makers need to take painting process to keep cooling models away from climate erosion. Unexpectedly, the external protection seal back the heat generated by LED lamps, speeding up the light attenuation of them.

The heat generated by LED chips / LED light sources are a type of small ranged concentrated thermal energy. For high-powered LED roadway lighting applications, the high input power and the high interface temperature are also heat sources with lamp bodies. Working in high temperatures for a long time, if cooling models cannot effectively conduct all heat outwards, not only the service life and performances of LED lights will be affected, but also the light attenuation will be more serious. LED street lights are normally used outdoors, taken into account of the climate factor, most of manufacturers added anodized shell protections or spray paint on the surface of lamp bodies, which is definitely block the heat dissipation.

LED test: errors frequently happened

Usually, in LED test, luminous flux, CRI, color temperature and power deviation are four major aspects that with relatively high failure rates. Unqualified quality testing results mainly concentrate in four aspects: 1. Electrical insulation cannot meet the corresponding requirements: insufficient internal clearance and creepage distance, with touchable conductors (not safely isolated). Especially for some small sized LED lamps, the compact structure forced manufacturers to ignore the requirements of electrical insulation. 2. Using drivers that cannot meet the safety requirements of LED power supplies, or using simple buck circuit to drive LED lamps. 3. Electromagnetic disturbance voltage exceeds standards: most of LED drivers use cheap but weak circuits without any anti-electromagnetic measures, leading to conduction voltage and radiation exceeding. 4. Cannot meet the light and color performance requirements. LED light-emitting principles have huge differences with traditional lighting technologies. Many designers only concerned about whether their products can send out light normally, but ignore the quality of photometric and colorimetric requirements, resulting in the huge differences in color temperature deviation and low CRI.

In LED test, lamps from one manufacturer may get different testing results in different testing processes. There are three main reasons that cause to such situation:

1) Testing system errors. This error is within the allowable range. Due to production process deviations, it is very hard for different testing system to stay exactly the same. There must be some errors. Traditional light fitting with error less than 1.5% are qualified. However, tests for LED lighting products have not been standardized. The permissible error range of LED lighting products is relatively vague, generally between 3% and 5%.

2) Error comes from different testing environment. Lamps’ working environment along with the different surface contamination will exert huge influence on testing results, 7%-8% error. Especially for some products which used light-emitting surfaces as the secondary optical lens. These products have concave and convex structures. Dust and dirt can easily accumulate on the surface, hardly to clean up, which seriously affect the luminous flux and furthermore the light distribution.

3) Errors come from equipment deviations and standard errors. Normal LED test includes: spherical integral devices, devices for light distribution measurement and equipments for light radiation. Spherical integral devices are used to measure the luminous flux of LED lights.

Advantages and selections of LED ceiling light

LED ceiling light use special process and G24 LED light source package, with higher luminous efficiency (120lm/W), better cooling effects, lower light attenuation (less than 3% after 3000-hour aging test), longer service life, safer, more durable and more reliable. LED ceiling light can be used in various conditions. Working temperature: -20 centigrade to 55 centigrade; working voltage: 12VDC/24VDC, 100-240VAC; Color: Cool White / Warm White / Natural White / Red / Yellow / Green / Blue / Multiple colors.

Compared with traditional ceiling lamps, LED ceiling mounted lights are more advanced in: 1. Energy-saving; the power consumption of white-ray LED ceiling lamps is only 1/10 of incandescent lights and 1/4 of energy-saving lights, with the same output luminance. 2. Longer service life; the average lifetime of LED ceiling lamps can reach up to 100,000 hours, very suitable for residential applications; 3. Frequent turning on/off the power will cause damages to energy-saving lights. But this condition will not occur on LED lights. Due to their special working principles, all of LED-related lighting devices can work under high frequency. 4. LEDs are a type of cold light source, using solid package, easy to transport and install, can be embedded within small and closed equipments, with low heat generation.

How to choose suitable LED ceiling light? Are there any knacks?

Radiator: how fast a lamp can outwardly transfer the heat generated by LED chips determine the light attenuation speed and the service life of LED lights. Working in high temperatures for a long time will speed up the light attenuation of LED chips. Main cooling methods for LED ceiling lights are mainstream integral heat sink, single cooling column for single lamp bead, external fan cooling mode. The size of radiator along with the quality of aluminum material affect the heat dissipation and also selling prices.

Lamp drivers / power supplies: in fact, the lifetime of power supplies usually determine the lifetime of the entire lamp. For the reason that, compared with LED chips, power supplies are more likely to fail. Normally, LED chips can have a working life of 50,000 hours. The lifetime of most power supplies is far less than this value. electronic components, circuit designs and other factors together determine the power factor, power efficiency, reliability, temperature rise and lifetime of LED power supplies.

LED test: sampling test results are not optimistic

From the current LED product structure and developing direction, the main testing standards for LED-related lighting products are focus on optical performance, electrical performance, terminal conductivity, radiation safety and service life. Optical performance is mainly related to the luminous flux, radiant flux, luminous efficiency, chromaticity coordinates, correlated color temperature (CCT), color rendering index (CRI). Photoelectric detection, light distribution detection, light energy detection, attenuation and anti-vibration test are five major normal testing for G24 LED lighting products.

However, according to a recent sampling LED test report, results are not satisfied. Recently, the Guangdong Provincial Bureau of Quality Supervision issued a product quality supervision and inspection testing report for self-ballasted LED lighting products. The final results showed that among 23 self-ballasted LED lamps, 17 are unqualified. The failure rate is as high as 73.9%. Failure items include accidental contact with live parts, the wet processing insulation resistance and dielectric strength, mechanical strength, fault status, chromatically tolerances, general CRI, harassment voltage, lamp power, heat resistance, interchangeability, power factor, the initial light efficiency / luminous flux, anti-blame capability and so on.

Awful LED test results happened frequently in recent years. Tracing the source, lacking of standards and immature testing systems mainly contribute to the high failure rate of LED sampling tests.

Although routine performance tests need to be taken before products leaving factories, not all manufacturers will follow testing standards strictly. On one hand, the majority of LED manufacturers do not have complete testing equipments. On the other hand, they need to take cost into account. Current large LED enterprises have nationally recognized LED test laboratories and relatively complete testing equipments. SMEs usually conduct several small simple LED tests (maybe a few hours), also lacking of necessary testing equipments. These phenomena led to the high failure testing rate mentioned previously and consequently a great deal of negative impact in the LED lighting market.

CRI should be greater than 80, otherwise the initial luminous efficiency cannot meet the requirements of energy efficiency to reach the energy-saving effect. Currently, some LED suppliers blindly pursue high luminous efficiency but ignore the light attenuation and total lifetime of their products, leading to the low service life of LED lighting products and the high failure rate.

Intelligent control will increase the added value of commercial LED lighting products

Mr. Carlost LEE, the Secretary-General of the European Photovoltaic Industry Association expressed his views and questions in a recent published report of “When LED Enters Into the Third Development Cycle”: “It is expected that the general lighting industry will be explosively grow in 2018-2020. Certainly, the business model of the product should be combined with their life-cycle. G24 LED lighting products have relatively long life-cycle. Thus intelligent control will increase the added value of commercial LED lighting products.”

LED lighting market is fragmented. Different application fields have different requirements to LED lamps. Take commercial LED lighting products and industrial LED lighting products for instance, the total production cost and appearance are two major factors that will be taken into account, while residential lighting products buyers are more concerned about qualities and lighting effects.

Currently, the penetration of automotive LED lighting products is still low. LED display industry has a relatively high market penetration. But we believe that the penetration of LED lighting applications in various areas will enjoy an increasing development from 2012 to 2020.

However, most of LED lighting products lack standard reference. Consumers are inclined to buy cheaper lamps but with low qualities, which will be easily failed after being put into service. This is one main reason why most buyers lost confidence in LED lighting products. It is not to say that every LED lamps should have a good quality. Good quality usually means expensive selling price. Consumers have right and should to know what type of products they are looking for. What kind of expectations that they should have on their products.

Incandescent replacing process is very simple. We now can see many CFL in hotels and hospitals as a replacement of incandescent lights. Generally, the service life of incandescent lights is around 6-9 years. Plus the good performance of CFL in lighting effects and luminous efficiency, it is very hard to persuade people to use commercial LED lighting products instead. LED makers need to put some additional value into their products to have them be accepted.

The lighting market is concerned more about the general lighting business. In order to further reduce the product cost, combining lighting technology, sensor technology, ITC and intelligent control together is a necessary developing step.

Intelligent control is the biggest advantage of LED roadway lighting applications

After decades of development, LED light source can send out high-brightness white light. The laboratory records for luminous efficiency reached up to 130lm/W, far exceeding the original 100lm/W. No matter in which way, G24 LED lighting technology is dramatically improved. High-powered white-ray LED lighting products have been widely used in general lighting applications, including LED roadway lighting applications. Compared with traditional road lamps, LED road lamps are more energy-saving and environmental friendly. However, as a new industry, LED roadway lighting still has many shortages. Service life and light attenuation are two main problems for high-powered white-ray LED road lamps.

To address this issue, Mr. Chunhai Wu, the technical director of the Shenzhen Lighting Environment Management Center suggested real conditions of 63 pieces LED street lights from 27 LED manufacturers in Shenzhen. From March 18^th, 2009 to March 5^th, 2011, in the case of normal daily using (normal switch on/off), there were 17 pieces lamps failed after two years, accounting for 27% of the total testing samples and 11 makers involved. Mr. Wu summarized: LED road lights’ aging tests should be performed on the ground (in factories, on production lines), and lighting attenuation tests should be finished in labs. LED road lamps are still weaker than traditional road lamps in stability. Certainly, different products from different manufacturers also have different qualities.

Mr. Haicong Zhang, chairman of the Shanghai Illuminating Engineering Society also affirmed the developing trend of LED roadway lighting industry. More advanced LED general lighting products have emerged in the lighting market in recent years. Through continuous improvement, these products are mature and stable. But LED road lighting products are still in the stage of immature.

According to Professor Lin Yandan from Lamps and Lighting Source Engineering Department of University of Fudan, LED road lights still have many advantages compared with high pressure sodium lamps. Intelligent control is their biggest advantages instead of energy saving. In order to satisfy large-scale applications, it is necessary to consider issues such as cost, reliability. If these problems are solved, LED street lighting industry will have a broader future.

With the continuous development of LED industry, LED street light industry will move toward the direction of specialization. The manufacture of LED lamps needs modularization. And also the modularization needs standardization.

LED beacon light start to emerge in the LED lighting market

Beacon light is a type of traffic lights installed in some beacon that ensure the safe navigation of ships and airplanes. They emit lights with particular colors and frequencies during the night, achieving particular irradiation angles and visual distances. Beacon light can be dived as fixed beacon, buoy, light boat and light house. Fixed beacons, buoys, light boats are usually used as navigation indicators or warming signals. Light houses issued identifiable signals day and night, helping ships to commit position measurements or also proving hazard warning information for ships.

LED beacon light is a new application in the market, which has been greatly promoted and received a lot of attentions from maritime sectors. Choosing right LED beacon light and currently using it is rather important. Expect for planar LED light source directly used in guide beacons, bridge beacons and rotating lights, most of LED beacons are round applications. Currently, beacon manufacturers all over the world used mainly use two parameters to identify performances of LED beacon lamps: light intensity of emergent surface and vertical divergence angle.

Used as light sources, LED components normally have certain beam angles, ensuring the initial light intensity within a given viewing angle. The light intensity – viewing angle characteristic curves indicates that LED components are single directional rather than full angle range spot light sources. Therefore LED beacon light must use special lens.

For LED round beacons, LED is a special light source. G24 LED chip is equipped with a small optical lens. The general purpose of this lens is concentrating light emitted by spot LED light source into a beam with a certain solid angle. Suppose a LED component with a solid angle of 30°, most of the light will be concentrated within this angle. The light intensity will be rapidly reduced outside this range. LED round beacons are a type of beacon lamps that evenly arrange LED components (with a certain solid angles) on the circumference with a certain diameter. If saying that this circumference (fully filled with LED components) is called light-emitting circumference, the Philippines Cornell Lens typically designed for LED round beacons will concentrate the light emit by the light-emitting circumference. Here LED chips are no longer LED sources.

Reasonable prices will contribute to the popularization of LED garden lights

We can find a variety of garden lights in the market, with all sorts of styles and light sources. Some of them are cheap but with poor quality conditions, some of them have good performances and qualities but really expensive. The over-expensive selling price of one good is the biggest obstacle of the promotion and popularization of this good. It is well known that price is the critical factor that determines the cost-effective of one good. Advantages and prices all together determine that whether one product can be easily accepted by buyers. As the new generation light source, LED garden lights started to emerge in the residential lighting market since 2010. There is no doubt that some of their incomparable advantages attracted a lot of attentions from merchants and consumers. But their expensive prices also kept them away from many ordinary families. Although, in the indoor lighting area, incandescent bulbs and fluorescent tubes are gradually replaced by corresponding LED lighting products, in the garden lighting area, traditional lighting technologies are still in the dominate position.

Below is the basic cost constitution of LED garden lights: the package cost occupies most part of the total production cost, about 50%-60%. Thus in order to control the production cost on a reasonable level, we need firstly choose a reasonable package structure. Since LED garden lights just entered the market, most current package structure cannot meet the special fixture design of garden lights. On the contrary, many designers have to created new shapes/constructions to meet the requirements of LED lights package structures, which also increase costs virtually.

Unlike other LED lighting products, LED chip cost occupies only a small part of total production cost, around 15%. Main costs are from package, cooling, structure, power supplies. Clearly, manufacturing process is the crucial section in the cost reduction. Reasonable structure design can optimize the performance of LED garden lights.

Design is account for 20% of the total cost. With the further development of LED technology, 5%-10% is more reasonable. For cooling designs, two issues should be noticed: a. shorten the cooling path between chips and external cooling devices; b. reduce thermal conductivity without affecting the cooling path.

LED light fittings need technological upgrade and support

Currently, LED light fittings are still in the early stage of development. Although LED lighting products have entered the industrial area, commercial area and residential area, the immature technologies still need further development, like output power, luminous flux, secondary optical design, cooling and other problems. Among them, cooling problem is the biggest difficulty for LED manufacturers. Limited by LED working principles, all structure accessories of LED lamps should have good cooling effects (good thermal conductivity) on the basis of safety. If using plastic materials, LED light fittings will soften and begin to melt within a few hours. Therefore, LED makers have restricted requirements on the LED light source structure designs and materials selection.

The commonly used cooling material in the market is aluminum/aluminum alloy. As a result of high costs (selling prices), some makers stated to find cheaper replacements with good thermal conductivity as well. Then PC covered LED lamps started to appear in the market. PC raw materials were firstly used as fixtures during the design for kitchen lights committed by Bayer Germany. They are durable and also have good thermal conductivity. The most important thing is that they are cheap.

Compared with traditional lamps, LED light fittings distinguish in many aspects: different deterioration speed in lamp bead (in high temperature, under high/low voltage); Electrical control. LED lights need to work under direct current; structure design, material selection, appearance design need corresponding variations. Insolated circuits/protections should be applied to guarantee the independent operation of LED light source and lamp body.

Many insiders indicated that, the main reason for LED light fittings hardly to be accepted by ordinary families is their expensive selling prices, which is caused by their high production costs. The light-emitting principle determines the cost of the product. The production cost of LED lamps is two times higher than traditional lights. Specifically: the over-expensive production costs of light source; restricted requirements to package structures and materials increase the production cost by nearly 50%. Semiconductor light emitting components are generally more expensive than traditional light emitting components. Due to lacking of core technology, the majority of our LED chips need to import from foreign companies. However, the production cost of LED chips occupied more than 60% total cost of the entire lighting fixture. The profit that China’s LED manufacturers obtained is rather limited.

LED home lights are still treated as assisted light sources in residential lighting applications

In 2009, the leader of the global lighting industry – Philips, formally promoted LED home lights, listing LED residential lighting applications as one of their main developing directs in the next ten years. Meanwhile, another household lighting giant – OSRAM also promoted dimmable LED ceiling mounted lamps, to seize the market in an early time. All these implied the potentials and hopes of LED home lights dominating the residential lighting market.

However, Professor Dahua Chen from the Lighting Research Institute of Fudan University indicated that “Although LED technologies have huge developing potentials in the lighting area, it still will take them decades years to become the mainstream in the residential lighting applications, mainly because of their bottlenecks in the research and development, and their immature in the product qualities.” Professor Chen did not hold out much hope on this part. LED can only play a supporting role in the household lighting applications.

LED is a type of solid-state semiconductor component, which can directly convert electricity to light. As the new generation light source, LED technology has many incomparable advantages: a. safe; LED must work under low DC voltage. LED home lights are much safer than other high-voltage lighting devices and more suitable for household applications. b. energy-saving; consuming only 80% energy but send out same light (same brightness/luminous flux) with incandescent lamps. Buyers can save their energy and money together. c. environmental friendly; LED is made from non-toxic materials, aluminum/aluminum alloy, causing no contamination to environment and recyclable. d. long service life. Theoretically, the average lifetime of LED chips can reach up to 100,000 hours (when light attenuation approaching 50%). Even LED lamps can have a working life of 50,000 hours. e. sturdy and durable; Basically, LED is just a small chip encapsulated in epoxy resin, then put into aluminum/aluminum alloy lamp fixtures. Compare with incandescent bulbs and fluorescent tubes, which are only under the protection of glass covers, LED lamps are much more durable. f. small sized; This feature enable LED lights to be made in multiple shapes and sustainable in various working conditions. This is also a designer-welcome feature, which provides more creative space for them. Some impressive lighting designs even can combine fixture designs with furniture designs, achieving the “invisible light source effect”. g. brightness and color adjustable; this feature can meet the special requirements of stage lighting as well as household lighting.

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月份：2013年1月