月份：2012年5月

Small LED manufacturers brings chaos to LED lighting market

With the rapid development of LED lighting industry, the competition becomes more and more fierce. Almost every day, there will be a new born small LED manufacturers take part into this stream, especially in indoor LED lighting market. LED lamps are electronic products. They need particular constructions and covers just like traditional lamps, and also require LED lighting sources (all kinds of LEDs connected in series or in parallel), AD/CD constant current diver, cooling fins made by aluminium or ceramics. Traditional lamps are just electrical products. The main job for traditional lamp manufacturers is design the construction of lamp shape. Lighting sources: bulbs, are usually produced by specific factories. Compare to traditional lamps, the manufacturing technique of LED lamps is much more sophisticated. LED company and LED manufacturers need to employ designers and engineers from electronic, photonic and construction area, as well as common workers.

 

With the rapid development of LED lighting industry, the competition becomes more and more fierce.

 

Since LED lighting market is an emerging market, there is no identical standard established in this field. This leads to a chaos in LED lighting market. Especially for those who just transformed from traditional lamp manufacturers to LED lamp manufacturers, or new comers. In order to reduce risks and the cost of production, they have to purchase LED broads, AC/DC constant current drivers and cooling fins from other manufacturers, then combined these components together to get their final products. Most small LED manufacturers continuous to use their old method: buy a bulb and a cover, then assemble them. It is really an easy way, but only suitable for traditional lamps not LED lamps. However, it is not to say that LED high bay lights cannot be produced in this way. In the matter fact, this clumsy and feckless manufacturing method has been widely accepted within those new-born small LED manufacturers. They do not have their own tech patents. They do not have their own technologies. They omit a lot of necessary tests. They have no certificates. They are actually LED processing factories rather than LED manufacturers. In order to attract more customers, they must reduce products prices. This malicious competition will finally give birth to the disorder of entire LED lighting market. Products from these small LED factories are usually unqualified. Most of them are probably failed during the work. Some even have potential safety hazards.

 

Analysis for light intensity of Light Emitting Diode

There three units can be used to present light intensity: Lux (unit of illuminance: the illuminace of 1L light within one cubic centimeter), Lumen (unit of illuminous flux: the illuminous flux of 1CD light within one square centimeter) and CD (unit of LED Street Light intensity: the light intensity of a fully radiated matter (bellow the platinum freezing point) per 1/60 centimeters).

 

The compact installation of several LEDs together will lead to the superposition of spherical lights of them.

 

Usually, CD is used to represent light properties of light sources like, filament lamps, LED lamps. Lumen is typically used to represent light properties of reflectors or objects with penetrability, like CD projectors. Lux is used in the photographic area. In fact, these three units are equivalent numerically, but need to be interpret from different perspectives.

 

In practical, light intensity is usually represented by units or transformed units that can be easily surveyed and mapped. LED displayers always use CD/cm2 as light intensity unit, together with observing angle. Generally, outdoor LED displayers require a light intensity higher than 4000CD/cm2 to gain an ideal display effect. While indoor LED displayers usually require a maximum light intensity between 700 CD/cm2 and 2000 CD/cm2.

 

The light intensity of single Light Emitting Diode can be represented by CD, together with observing angle. Light intensity has nothing to do with light color. Normally, the light intensity of single LED range from several mCD to 5000 mCD. The light intensities given by LED manufacturers are measuring values in particular conditions: under 20 mA working current, observed in best visual angle, the most bright point in central. The beam angle and intensity distribution are determined by the form and position of lens mounted on the top of LEDs. Generally speaking, Light Emitting Diode with a small beam angle will send out brighter (higher light intensity) lights.

 

The compact installation of several LEDs together will lead to the superposition of spherical lights of them. However, the entire spherical intensity is evenly distributed. We call it average spherical luminous intensity (MSCP). When we measure MSCP, we need to take LED visual angle and the number of LED down lights into account. And multiple the maximum spot light intensity (given by product specifications) with 30%-90% (depends on the packaging), then we can calculate the approximate light intensity of single Light Emitting Diode.

How Light Emitting Diode send out lights with different colors

Light Emitting Diode (LED) is a type of electronic components that convert electric energy into optical energy. Most LED Projects can send out lights within the range of infrared rays and blue rays. At present, Light Emitting Diode sending out purple rays and even ultraviolet rays has been invented. Besides, LED manufacturers also made a kind of white LED by coating a layer of fluorescent powder on a blue-ray LED. In the next section, we will discuss more details about color manufacturing technique of LED Street Light.

 

Light Emitting Diode (LED) is a type of electronic components that convert electric energy into optical energy. Most LEDs can send out lights within the range of infrared rays and blue rays.

 

Light Emitting Diode made by different materials can emit photons with different energy. In other words, wavelength (color) of the light can be controlled by LED manufactures. In history, GaAs is the first materiel used to make LEDs. The minimal working voltage in forward bias is 1.424V. LEDs made by GaAs can only emit infrared rays. Another commonly used LED material is GaP. LEDs made by this material have a higher working potential: 2.261V, sending out green lights.

 

Based on these two types of materials, a new material construction GaAs1-xPx (x represents the ratio of phosphorus to arsenic) was used in the early LED industry. This new material construction realized multi-colored LEDs ranging from red rays to green rays. The wavelength (color) of the light is usually determined by the band gap (potential) PN junction, like red LED with a material construction of GaAs0.6P0.4, orange LED (GaAs0.35P0.65) and yellow LED (GaAs0.14P0.86). LEDs using material of arsenic, phosphorus and gallium were typically named “three elements LEDs”.  Blue LEDs (GaN), green LEDs (GaP) and infrared LEDs (GaAs) are named “two elements LEDs”. The latest manufacturing technology is combining Al, Ga, In and N together as AlGaInN. LEDs made by this new four-element-compound can send out lights ranging from infrared rays to ultraviolet rays.

 

Some people may ask: how can a Light Emitting Diode send out white rays? In fact, white is a combination of red (21%), green (69%) and blue (10%). However, due to the manufacturing technique, it is impossible for LED spot Lights to emit purely red/green/blue rays. Thus color matching is necessary. Workers need to combine three colors in proportion, and meanwhile control the light intensity of them respectively to create approximate white rays.

How to measure the temperature of LED PN junction? (2)

Some people suggest that the temperature span should be larger than 50 degrees when measure the PN junction temperature by using voltage method. The voltage-temperature relation will be linear in normal working temperature range of LED Lights, it is useless. The room temperature is 25 degree. According to the suggestion mentioned above, next measuring temperature be around 75 degree. However, the upper limit of the normal working temperature of LED PN junction is 70 degree. Is there any reason for us to measure the voltage-temperature factor in 75 degree: a cannot-be-reached temperature under normal use? It is impossible for a LED manufacturer to build a very sophisticated temperature-controlled lab. Thermostatic equipments can only keep the temperature within a range. It is also impossible to obtain accurate measuring results by using them.

 

Some people suggest that the temperature span should be larger than 50 degrees when measure the PN junction temperature by using voltage method.

 

However, if we are unable to fix the surrounding temperature, we can obtain accurate voltage-temperature factors through the relative temperature derivative, and consequently working temperature of LED PN junction. Firstly, we need to record the room temperature, namely the pre-working PN junction temperature. This temperature can be treated as the initial junction temperature corresponding to the initial voltage. Secondly, apply a voltage on both sides of LED Products, wait until the entire PN junction working in a stable condition, then read the voltage value. In accordance with measured voltage and the predefined voltage-temperature factor, we can calculate the increase value. Add this value together with the room temperature measured previously, then we have the final LED PN junction temperature, which is quite closed to the real value. Overall, voltage method is much more precise than thermal image method.

 

Formulas for thermal resistance method given as followed:

Rθ = (Tj-Tc)/P

Rθ is the thermal resistance of PN junction. Tc is the package temperature. P is the power consumption. Rθ andTc are fixed values given by the production specification. Once we know them, we can calculate the LED PN junction temperature Tj through this formula. There is another problem, how can LED chip manufacturers measure thermal resistances? They need to know junction temperature at first! In fact, this method is not used to calculate PN junction temperature. On the contrary, it is used to calculate thermal resistance though junction temperature. Most LED High Bay manufacturers still use voltage method to measure junction temperature.

How to measure the temperature of LED PN junction? (1)

More and more people realize that estimating the specific temperature of LED chips by measuring LED lamps covers temperature is inaccurate. However, how to get the exact temperature of LED PN junction? At present, there are three commonly used PN junction temperature measuring methods: thermal resistance method, voltage method and thermal imagine method.

 

More and more people realize that estimating the specific temperature of LED chips by measuring LED lamp covers temperature is inaccurate.

 

Thermal imagine method requires very expensive instruments which cannot be afforded by ordinary people. However, using thermal imagine method to measure PN junction temperature cannot guarantee the accuracy of results. Thermal imagines can only display the general heat distribution. There are many other things need to be taken into account to get the accurate temperature value. Surface emissivity is the main factor. In order to measure accurate temperatures though thermal image, we need to set a surface emissivity value at first. However, in the surface of LED Street Light chip, there are several materials. Different materials have different surface emissivity values. Even if every exact surface emissivity value was known by us, which one should be chosen as the reference value? Meanwhile, if we successfully obtain the accurate temperature by thermal images, it is a surface temperature, what about the temperature of LED PN junction? No matter what kind of optimization is taken, thermal imagine method can only get an approximate value. Therefore, it is a not commonly used method to measure temperatures of PN junctions. In the next step, we are going to do some introductions about thermal resistance method and voltage method.

 

Voltage method:

According to semiconductor theory, the voltage of PN junction is not only a function of temperature, but also a function of current. And the relation between junction voltage and junction current is not linear, which means voltage-temperature relations are different under in different current. Thus, if we intend to measure the temperature of LED PN junction, the working current needs to be known at first. Before measuring PN junction temperature using voltage method, we need to set a fixed constant working current for LED High Bay. Then put them into a thermostatic equipment to offer a constant working temperature. The last step is reading the measuring voltage value. Change into another temperature, repeat this operation once again. Normally, 3-5 measuring results can give out a relatively accurate relation between voltage and working temperature of LED PN junction, namely voltage-temperature factor.

Temperature influence for LED PN junction

As we all know, light color of LED can be determined by materials used in n-type region and p-type region, and light intensity is determined by the number of carriers within LED Street Light. Carriers’ number is not fixed in diodes. Temperature can exert a significant influence on it. With the increase of temperature, the intrinsic excitation effect will be enhanced. More electron-hole pairs will be generated in n-type region and p-type region respectively. This additional electron-hole pairs will change the width of LED PN junction as well as internal current.

 

As we all know, light color of LED can be determined by materials used in n-type region and p-type region, and light intensity is determined by the number of carriers within LED.

 

Apply a forward bias voltage on LED High Bay, a certain amount of heat will be generated. Thus more electron-hole pairs will be created during this process. This intrinsic excitation can happen within p-type region, n-type region and space charge region.

 

Intrinsic excitation within p-type region: electrons created by intrinsic excitation combine with holes provided by the positive potential connected to the other side of p-type section, leading the reduction of PN junction. This kind of combination can generate heat energy.

 

Intrinsic excitation within LED PN junction: if an electron-hole pair is generated within PN junction, the electron will be impelled into p-type section due to external electric field. This electron will combine with a hole provide by the positive potential. Since this kind of combination cannot provide enough potential energy to generate visible light but infrared rays. Some parts of these infrared rays are absorbed by LED and consequently converted into heat energy, the other parts radiated into the air. Scientists also name this type of combination as invalid combination.

 

From the analysis of above two intrinsic excitations, a part of holes provided by power supply will be combined by electrons created by intrinsic excitations. These holes cannot pass PN junction. Similarly, a part of electrons provided by power supply cannot pass PN junction due to intrinsic excitations. Intrinsic excitation within LED PN junction is the chief culprit for this invalid combination. Thus, only a part of carriers provide by power supply can pass though PN junction containing enough potential energy (reach the band gap) to emit visible lights.

 

However, if the working temperature is higher than a certain threshold value, optical quenching phenomenon will be caused. Except for invalid combination caused by intrinsic excitations within LED PN junction and LED Panel, tunnel effect is another factor. When carriers concentration is too high, the Fermi level of p-type region can reach up to or even exceed the Fermi level of n-type region. So electrons have no need to pass PN junction and reach to p-type region directly. The energy released by the combination of electrons and holes will be lower than the band gad, leading to the optical quenching phenomenon.

Why heat is generated within LED PN junction? (2)

3.  Electrons in the edge of p-type section. Electrons pass LED PN junction and finally reach the edge of p-type section. Most of them will be captured by the large amount of holes within p-type section. Since electrons have higher potential energy than holes, after being captured by holes, this potential energy will be released as the form of electromagnetic wave (LED Street Light). The light color all depends on the material of diodes. Different diodes has different band gap (different potential energy), which can emit lights with different wavelengths. As we all know, wavelength determines the color of the light. Wavelength within visible range can be seen by human eyes. Electrons from n-type section originally have a higher potential energy than holes within p-type section. In addition that electrons’ potential energy is raised when they pass though the space charge region. It is quite easily for them to reach up to the band gap potential energy. Notice that, this potential energy gained by electrons has nothing to do with external electric field, only decided by LED Projects materials used in n-type region and p-type region.

 

Electrons in the edge of p-type section. Electrons pass LED PN junction and finally reach the edge of p-type section. Most of them will be captured by the large amount of holes within p-type section.

 

4.  Electrons within p-type section. Most electrons will be combined by holes when they enter p-type region. This process will cause the reduction of holes in the edge of p-type region. Since we add a forward bias voltage on LED PN junction, this reduction can be immediately supplemented by holes given by the positive potential connected to the other side of p-type region. External electric field exerts a forward force on electrons and make them accelerate, collide with nucleus and other electrons within p-type region. During this process, energy created by external electric field is converted into heat energy.

 

According to the above analysis we can see that the light energy generated by electron-hole combination is not decided by external electric field by materials used in p-type section and n-type section. It is a fixed characteristic of LED PN junction. On the other hand, all of heat energy created by PN junction is a conversion of electric energy from external electric field. It is an inevitable outcome of LED. Thus a good cooling system is very important for LED lighting applications, especially for those LED lamps with high power consumptions. For the reason that LED cannot work in high temperatures.

 

Why heat is generated within LED PN junction? (1)

LED (light-emitting diode) is a kind of one-way conductive electronic component. Generally, diode is a PN junction composed by a p-type semiconductor and an n-type semiconductor. An equilibrium condition is reached within the space charge region in the condition of zero bias.

 

LED (light-emitting diode) is a kind of one-way conductive electronic component. Generally, diode is a PN junction composed by a p-type semiconductor and an n-type semiconductor.

 

At room temperature, why do carriers within LED PN junction generate heat along with light?

  1. Electrons in n-type section. Under positive bias (the normal operating condition for LED Street Light), the negative potential connected to n-type section will continuously provide electrons to PN junction. In matter of fact, most of the electrons provided by the negative potential will be “swallowed” in n-type section. 80%-90% electrons will be captured by nucleus or collide with other electrons. Once electrons were caught by other nucleus, they would lose the original speed given by external electric field. Part of them convert into heat energy, the other part is transferred to adjacent electrons as kinetic energy. Then these “new freed” electrons will repeat their predecessors’ destiny. A substantial amount of heat will be generated during the constant repetition of this process. Thus we can see that most of the energy provided by external electric field converts into heat energy of nucleus at last.
  2. Electrons in space charge region (PN junction). There is an internal electric field in space charge region which is opposite to external electric field. Therefore,LED Tube internal electric field will created an inverse force on electrons as opposite as external electric field dose. However, since the forward force generated by external electric field is much greater than the backward force generated by internal electric field. Electrons are still impelled in the original direction in LED PN junction. In the view of LED Products energy transmission, internal electric field creates negative work on electrons. In other words, PN junction absorbs kinetic energy from electrons and converts them into heat energy. The source of electrons’ kinetic energy is the external electric field. On the both sides of space charge region, there exists an energy level difference. Electrons need to increase their energy level as well as overcome the PN junction resistance. The energy applied to increasing the energy level is from nucleus within LED PN junction. Since energy is absorbed by electrons, the vibration amplitude of nucleus will reduce, leading to a temperature reduction. However this “cooling down” is trivial compare with the heat generated by the negative work from the internal electric field. On the whole, LED PN junction will generate a large amount of heat in their work.

 

The global duration of bright sunshine push up the plant lights led factory

At this stage, the global climate change intensely, and the extreme weather are more frequent than in modern times. From 2011,2012 Northern Hemisphere increasingly getting colder, From the perspective of clouds covering rate, rainfall intensity in 2011, the deduction time of lighting will be a harmful factor for the agricultural development. LED Grow lights and plant lights led factory have become another remedy way in the agricultural academia.

Japan’s central government, local government (County Road), starting from the 2011, to coach local agricultural industry, plant factories to develop grow light manufactory.

The global duration of bright sunshine push up the plant lights led factory

Japan’s government put forward policy of remedying plant lights led factory in 2009, total spent 14.6 billion(Ministry of Agriculture, Forestry and Fisheries of about 9.6 billion yuan; the Ministry of Economy, Trade and Industry is about 50 billion) to build planting factories. Up to the 2010, an additional 1.04 billion yen completely provided to artificial plant factory with high added value technology development. Benefit from the subvention, the number of plant factory from 50 in 2009, gradually increased to more than 100 specifications, which include artificial light and the sun-light-type plant factory.

The main coause of the prevalence of plant lights led facotory.

Firstly, the high cost of agricultural land.

Secondly, the high temperature,LED High Bay light, in summer.

Thirdly, resources and related equipment is easier to obtain. It is also contributed the main cause of the plant factory.

Fourthly, Greenhouse hydroponic leafy vegetables in Japan have a certain market. Using plant lights led factory to cultivate vegetables, consumers can be fully accepted.

Fifthly, The large demand for high-quality vegetables among consumers, and they are willing to pay.

Sixthly, The related power consumption equipment upgrade, especially the performance of light and air-conditioning equipment has been greatly enhanced.

Seventhly, Japan’ s government strongly advocate and promote the high percentage of the subsidy, and regardless of enterprise or farmer.

However, plant lights led is not only adopting LED Street Light source.  The early planning is to use fluorescent lamp which is in accordance with a specific wavelength to supply the plant. In addition, it has been developed a long time. And the more power, energy saving, better ability to specify the wavelength of the LED lighting considered the advantage of combining variety of wavelength, which become the expectancy of plant lighting. At the same time, the benefits of long-term use of energy-saving, the less replaced time than the fluorescent tubes are more obvious.

Canada New Glasgow: 1200 street will make led lamp replacement of the LED lights

In the spring of this year, the Democractic Party government of Canada launched legislative rule that the roads and highways must use LED lights. And regulated the municipality will be completed the replacement projects within five years. As early as last year, Cao lisa MacDonald indicated that the Government has sufficient funds which can be fully support the led lamp replacement projects.

It is reported that in the coming weeks, the city of New Glasgow, Canada will be replaced all the street high-pressure sodium lamp with LED street lights.

Canada New Glasgow: 1200 street will make led lamp replacement of the LED lights

Last year, the town of New Glasgow tried out 59 LED lamps. The result shows that the effects LED lamp lighitng is more significant than the traditional light. If all high pressure sodium lamps are replaced with LED lights, then the annual carbon dioxide emissions will be reduced 287 tons for local town. However, at present, only the New Glasgow introduced a led lamp replacement project, other municipalities  are still conducting the investigation where can be better choices.

Vastervik Cao Scott Fraser (Westville CAO Scott Fraser,), said that last year’s study shows that LED lights really saved energy and money in the town of New Glasgow. Trenton, Pictou and Pique municipalities are looking forward to the implementation of the LED conversion scheme.

New Glasgow nearly have 1200 streets to participate in the led lamp replacement plan. The municipal government has signed installation agreement with GLahill(a company’s name). The cost for replacment projects is about  $ 820,000 this time. And Nova Scotia (NovaScotia) Department of  Energy will invest  $ 120,000. Miss Cao LiSha said, the led lamp replacement project will get back to revenue after six years later.

According to a worker who manage the LED Lights introduced that the led lamp replacement projects spread from last years’ December. She said, the install street lamp in the past years are sodium lamps, at present, all lamps are replaced to LED digital lamps. Although the power is less 400W, but it is more brighter than 500W’s sodium lamps. Some workpeople are moving different accesorries, some install street lamp, some make the installed lamps set upright. The two sides of streets are presented persperous scene.