日期：2012年5月9日

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.