2014年03月28日

LED structure, properties and applications


LED light-emitting semiconductor chip as the use of solid materials , when both ends with a positive voltage, the semiconductor carrier recombination occurs , the excess energy released due to the visible light photons emitted . In recent years , LED lights has been rapid development , some products have entered the commercial stage , bring revolutionary changes to the indoor and outdoor lighting.


The early 1960s , people have mastered the method of the semiconductor material can produce light : forward biased GaAs junction diode can be used as a radiation source . In 1964 , the use of GaAsP materials, developed a red light-emitting diode (λp = 650n m), luminous efficiency of 0.1lm / W, the drive current of 20mA , the luminous flux is only a few thousandths of lumens.


To the 1970s , developed a green (λp = 550nm), yellow (λp = 590nm) and orange (λp = 610nm) of the LED panel lights, luminous efficiency of 1lm / W. Monochrome LED booming , making it on the big screen display , traffic lights , instrument displays and other fields are widely used . Unfortunately achieve breakthrough full-color display Blu-ray yet .


In the early 1980s, developed the GaAIAs of the LED, making the red LED spot light efficiency of 10lm / W.


1994 , the development of GaN based blue and green light-emitting diode according to the synthesis of three -color theory, the full color display and semiconductor lighting becomes possible. For general lighting purposes, people need more white light. In 1996, Japan's Nichia Corporation pioneered the development of white light-emitting diodes, brought great hope for the LED tube lighting into a wide range of fields, as a milestone in the history of the development of LED lighting .


After several years of development , such as performance -color LED light efficiency has been further improved, making its decorative lighting and other fields has been widely promoted and applied. Several key features colored LED 's shown in Table 1 .


Currently, the white LED light efficiency is not high, but growing fast. According to the relevant information on: 1999 Japan developed a luminous efficiency of 15lm / W of LED; 2001 United States developed a luminous efficiency of 40 ~ 50lm / W of LED, even more than incandescent and halogen , fluorescent light proximity effect . Single LED power is not big enough , only 1W more , it can not be widely used for indoor and outdoor lighting, but IPL LED decorative lighting applications in the field has matured. Experts believe : white LED light efficiency is only reached 50lm / W or more, and to enhance the single white LED power , in order to truly be widely used in the lighting field . Currently, the white LED is moving towards high efficiency, high brightness , high power, high color rendering index of the direction of development . Currently , the world focused on the research and development of white LED in the near future , white LED light efficiency is expected to reach 100lm / W, and even upgrade to 200lm / W or more, then , LED will occupy a dominant position in the field of lighting .


2, LED structure and working principle


Mainly by the PN junction LED chip , an electrode, an optical system and other components and accessories . Called LED chip emitting body , which area is 10.12mil (1mil = 0.0254mm2).


In a clean epoxy resin -encapsulated semiconductor chips. P -type semiconductor PN junction end of the positive voltage , the N-type hole will flow terminal electron flow from the P-type N -type terminal end . When electrons pass through the wafer , the negatively charged electrons with positive holes move to the region of holes and electrons can be combined directly in the binding process, the release of energy in the form of a photon of light , which is the LED light-emitting principle . In addition , after some LED electrons accelerated in the crash , the process can also be free to release energy and light. Energy ( band gap ) between the electron and the hole larger , the higher photon energy produced . Most conventional light emitting diodes using gallium arsenide (GaAs), gallium phosphide (GaP) , or combinations thereof crystals (GaAsP) , etc. group III-V semiconductor.


LED luminous efficiency, color and optical properties of semiconductor materials and processing technology related. Incorporation of P-type and N -type material in the different impurity materials , it can be a different single wavelength of the light emitting diode LED , and electrical properties will be different. According to the optical principle , by a continuous white light spectral composition , therefore , impossible to produce a continuous spectrum emitted directly single white LED. In the lighting field, the most widely used is white , so white LED research and technological advances related to LED bulb lighting in the area of application and promotion.


A single light emitting diode LED optical system comprising a transmitter parallel polarizers, etc. through the mask . The optical system of the LED light beam or a parallel light beam emitted angle ( Figure 1 ) . Thus, changing the geometry of the enclosure dome , the LED can change the beam angle .


Two kinds or three kinds of monochromatic LED may be formed of a synthetic white light generated by the LED to be mixed together by a few monochromatic LED , synthesized according to the principle of the three primary colors white light , as shown in Table 2 . Currently, there are three main commercial white LED light way :


( 1 ) coated on the InGaN blue wavelength 460nm YAG fluorescent material layer of the grain , using the blue LED irradiating the fluorescent substance , a yellow wavelength of 555nm can be generated , and then use the principles of the lens can be complementary to blue, yellow mixture , the can emit white light (see Figure 2 ) . However, a strong blue spectrum spectrum , the lack of red spectrum , color rendering index Ra to reach 70. This is currently the most widely used white LED production principle .


( 2 ) excited by ultraviolet chip RGB trichromatic phosphor luminescence mechanism with three -color fluorescent similar. Changes in the ratio of phosphor composition , you can get a variety of color temperature of white light , the color is good.


( 3 ) of the RGB three primary colors chip package together , changing the light emission intensity ratio of the three, can be obtained at any temperature of the white ( Figure 3 ) , but the product quality is difficult to control . Consistency of product performance is poor , vulnerable to environmental impacts.


" Figure 4 , Figure 5" shows a schematic view of the white LED and the light emitting structure : GaN chip and the yttrium aluminum garnet phosphor (YAG) package together, blue LED chip mounted on the bowl-shaped reflection chamber , the cover substrate a thin layer of resin mixed with YAG phosphor. After power , GaN chip emits blue light (λP = 456nm, Wd = 30NM). After part of the Blu-ray excitation YAG phosphor emits yellow light , yellow light mixed with part of the blue , you get white light. For InGaN / YAG white LED, the YAG phosphor by varying the chemical composition and adjust the thickness of the phosphor , it is possible to obtain a colored white 3500 ~ 10000K .


3 LED 's performance


High luminous efficiency of 3.1 and has great room for improvement


Monochrome LED luminous efficiency has reached 100lm / W or so, with the highest light efficiency sodium, metal halide fairly . Currently white LED light effect , although only 15 ~ 50lm / W, but it has gone beyond incandescent, halogen light efficiency, close to fluorescent light efficiency . Experts predict that in the most promising areas of illumination white LED luminous efficiency , as well as a great room for improvement . Will set off a revolution in the lighting field .


3.2 Response time is short


Incandescent response time in milliseconds , LED response time places nanoseconds . This feature makes the LED decorative lighting as a whole can change color in an instant consensus reached dreamy effect .


3.3 Energy saving


LED supply voltage DC 6 ~ 12V, single-tube power 0.03 ~ 0.06W, current 15 ~ 18mA. In the same lighting effects , the power consumption of incandescent 1 / 8 , Fluorescent 1/2 . Such as the use of LED replacement of existing incandescent and fluorescent lamps, will get a very considerable economic benefits. After further improve LED light efficiency , energy saving effect will be more significant.


3.4 long life


LED small size , fast response , light weight, epoxy resin , durable , with an average life of 100,000 hours , you can use 5 to 10 years. Easy to install concealed , while maintaining a small amount , low maintenance costs .


3.5 Application flexibility


Can be made as points, lines , surfaces and other forms of light products .


3.6 beam directional


Each LED light bulb can be controlled with a certain directivity. No glare and soft light, the built-in micro-processing system to control light intensity , adjusting the light way .


3.7 Variable Color


LED light color can be changed with the current size . LED can be easily modified by chemical methods , adjust the material's band structure and band gap , to achieve red, yellow , green, blue , orange, purple and other multi-color light . This feature is very useful in decorative lighting .


3.8 Safe and reliable pollution


LED low voltage, safe to use, especially for public places. Because it is a cold light source , while working low heat, no infrared and ultraviolet radiation. LED mercury , sodium and other metallic elements endanger human health , is a truly green lighting.


4 LED problems to be solved


Although the LED has many excellent properties, but there are still some problems to be solved .


( 1 ) improve the efficiency of white LED light


So single white LED light effect as soon as possible from the current 50lm / W or less raised to 100lm / W or more, to get more energy-efficient economies ;


( 2 ) increase the power of single LED


The current application of the LED, single 1W less power in general , in order to meet the needs of more than just a combination of the LED decorative lighting, traffic signals and lighting needs. To really make LED lighting is widely used in the field , we must improve the single white LED power . Especially in outdoor lighting , the widespread use of high-power light source , get a higher flux. Therefore , LED lighting to really enter the field, especially into the outdoor lighting field, there is still a long way to go .


( 3 ) improve white LED color


Compared to the white light emitted from the LED with natural light , there is still a gap. Ingredients containing blue light emitted from the LED white light , giving visual unnatural feeling. Incandescent light , yellow light contains a strong component , gives a warm feeling. Therefore , to further improve white LED color rendering index, reducing white blue component , due to increase yellow component , is one of the future to improve the quality of the white LED light an important issue .


( 4 ) reduce the price


Reduce LED prices , is also a problem that must be addressed . Currently use a variety of LED decorative lights, marker lights , traffic lights , etc. , are made on more than just adding accessories LED combination lamps made ​​. LED lights set the price is the same set of general lighting lamps lighting effect several times , it is difficult to be accepted by the majority of consumers .


Status of white LED and improved methods shown in Table 3 .


5 LED Applications


Currently , spectral color LED products , has been covering the entire visible spectral range , and high luminous efficiency, color purity , high brightness , good direction , color variable , such as excellent performance , widely used for decorative lighting and signal flags fields.


The white LED technology performance to be further improved, so white LED indoor and outdoor lighting has not been widely used, but experts expect : According to the current trend of rapid development of LED technology , white LED is expected in the near future , become the incandescent a new generation of lamps, fluorescent lamps , gas discharge lamp lighting together accounted for hegemony dominance .


LED has two external power supply ways: one is LED and other high-grade electronic components together into a reliable light-emitting line is directly connected


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2013年11月19日

Correct Usage of Parental Control Software to Ensure Kids Online Safety

Since the rapid development of our society, many aspects of people’s life have been facing great changes. Virtual world created by network has become as important as the real world. As a parent with a child, you are inevitably going to be worried about what is going on in his or her cyber world. So, how do you truly find out, without overstepping your boundaries? It's a good question, and one that more and more parents are struggling with.

One solution to finding out what exactly is going on is to install computer tracking software. There are many available software for use, some monitor website visits while others monitor instant messenger services. All can be installed and run in the background so your child won't even know they're being watched. Some would argue that this goes too far, while others say it's a personal choice.

There are many parents who report using software that has enabled them to nip potential drug and alcohol problems in the bud. Others say that they've been able to steer their children clear of parties where inappropriate behavior will be involved. One of the most disturbing reports to date is a father who discovered, through the use of monitoring software, that his 13-year-old daughter was having a sexual relationship with her 37-year-old teacher.

But when does parenting become paranoia? And when do you begin to infringe on your children's right to privacy? These are all important questions that parents face when delving in to their children's online activities. Child psychologists indicate that, since it is your responsibility to protect your children, it is absolutely acceptable for you to use such software. However, you should discuss it first with your children and tell them that you will be checking up on them and also lay out very clear ground rules about being on the Internet and what's acceptable.

If you choose to not go so far as monitoring software, do consider using a filter on your Internet connection. While this will not tell you where your children are going and who they are talking too, it will block objectionable material from popping up on their screen. Also, check your web browsers history to see what pages they've been looking at. If your 15-year-old visits a porn site once, don't freak out; you'll only alienate them. If, however, you see multiple visits, it's time to have a serious conversation.

If you have more serious concerns about what your kids are up to online, a new breed of parental control software may tempt you. Parental control software is the top pick for you to monitor your child's online behavior and protect them online. It's an ideal spy software package to ensure you have the control you need over your child's online behavior. The completely invisible to your child and hardly traceable recorder module will tell you when, how and what they did on the Internet.
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2013年09月23日

What Can You Do to Protect USB Security?


As the rapid development of information technology, information security now focuses on popular cloud concept such as: cloud computing, cloud storage. But for most of the enterprise that, solve the enterprise of the most widely applied USB and mobile storage equipment data security protection is imperative. USB encryption is still should be pay attention to and choice of data safety protection.



How should you do to choose a premium USB encryption product? What kind of functions and characteristics USB disk encryption software products should have? There are several tips offered below.



Firstly, all data of USB and mobile devices which want to internal into the network, must pass the high strength encryption protection, even if confidential documents disclosure or loss of U dish, the other side also can not open to view, prevent all kinds of leak and accidental loss brought about by the USB security incident.



Secondly, USB and mobile storage equipment must be registered before use, through the service issued by the strategies to control the use of USB, not registered user can't use in the company, strictly control the enterprise internal Custom USB use, prevent illegal equipment access enterprise internal network, to prevent the network connection bring risk of Trojan virus spread.



Thirdly, the widely use of USB is because its small size and large capacity, portable characteristics, if USB to control and manage the let customers use up very trouble then use of USB disk run counter to the original intention. Therefore, the mobile storage equipment safety protection at the same time, can't affect the user use mobile storage equipment legal data storage and exchange use habit and convenience. This needs the custom USB can provide flexible and controllable access control strategy, and tie-in high fine-grained access control, to meet the needs of the user many applications scene, to ensure safety in the basis of the really does not affect customers to use convenient.




Fourthly, administrators should be able to convenient through the control center to check all client registration information, the customize USB connection equipment, burners, cd-rom, mobile hard disk storage equipment, etc, and the equipment to monitor management operation, ensure that the company's core data will not be through the peripherals leakage.



Besides, a premium encryption USB flash drive should have extensive compatibility, and all kinds of operating system and application software, IT deployment environment compatible, don't change user management operation habit.



Customized encryption USB just solve some current enterprise face some of the most urgent, the most serious data security needs, only for the enterprise users common data leak the protection, it is far from perfect. Enterprise only use unified platform for risk and safety management, and grasp the enterprise the current overall security situation, adopting the specific measures of protection can maximum limit reducing enterprise data security risk.

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