LED Light文章 2.docx

1、LED Light文章 21. How To Choose A Suitable Led DisplayThere are so many LED display manufacturers here in China. there is a saying:60%70% LED display are made in China,and 60%70% LED displays are made in Shenzhen,China.but till now, no one can show the valid data about the information.luckly, I am in

2、Shenzhen, and engaged in this field for nearly 2 years.Sometimes, its more difficult buying than selling.(sorry, i am not good at English) I met customers from USA,Poland,Iran,Turkey etc, generally speaking, they spent about 1 week in China. and they visited more than 10 factories here,that means, t

3、hey visited 1.5 factories everyday,average.thats not a easy job, every factory will give you different information, its a big problem that how you get the useful and correct information.i am sure, what suppliers give you is not always correct all the time, because whom you discuss with is always sal

4、esman, and some salesman dont know very well about this industry themselfes, for another word, they are not profeesional. but that not means the factory not professional. in Shenzhen,China, many owners of factory, they have been involved in this field for more than 10 years, they are pioneers.also,

5、they are demostic sales man years ago. but a big problem is they cant speak english, luanguage is big obstacle for them. take my boss for example, he engaged in this field for more than 10 years, he knows very well about this industry, but he cant join the discuss. sometimes, our customer asked me,

6、where is your boss?i said:sorry, he is not good at english. it will be much better if discuss with my boss. it happens.Ok, let get to the point, how to choose a suitable LED display. maybe is a old topic. but as far as i know, many friends have no idea about this before they came to China. i choose

7、the wordsuitable, not good. because different customer has different requirement. good does not mean suitable, but suitable does means good for you.it always considered as a project when you want buy a LED display. so you should have a budget on it, 100,000, 80,000 USD? something like this. then, it

8、s the details about your project, such as:1. where will be the LED display installed? indoor or outdoor?2. what message content is needed? videos, photos, or just characters?3. what dimension will be your screen? width, height?4. what will be the minimal viewing distance from your screen to the clos

9、est spectators?5. whats the distance from LED screen to control system?6. whats the installation type? inlay, pole, or something else?after these information, you can get a general solution from the supplier. for example,you want an outdoor display for ad displaying, viewing distance is about 17 met

10、ers, you prepare 100,000 USD for it, and the supplier may recommend P16,Cree LED chips, 40 square meters. ok, this solution sounds good, then you may wanna check the quality, this is most important for you. you dont want spend 100 USD for a piece of paper. so, how to judge the quality, maybe you can

11、 consider based on below information:Key Factors:1. Smoothness(plantness on surface)Keep the smoothness within 1 millimeter to insure the image not been curved.it depends on assemble tech.2. BrightnessFor indoor LED display, it should be more than 800cd/sq.m and for outdoor, it should be more than 1

12、500cd/sqm. If brightness too low, the image will be totally vague.brightness depends on LED lamps you adopt and other factors3. viewing anglegenerally speaking, for outdoor displays, viewing angle for horizontal is about 110 degree, and for vertical is 90 degree. the larger the better.4. white balan

13、ce.To show a pure white color, the ratio of RGB is 3:6:1, wacth if there is blue or red color in white color. This factor mostly depends on control system and LED lamps5. color restorable.The color on LED screen should consist with display resources to keep a good image.6. malfuncation dot, mosaicma

14、ke sure there is no dead dot and mosaic on displayThese factors are very important when choose a LED display, its diffecult to maintenance for some unprofessional customers.2. Improve The Thermal Structure Of White Light Led LifePast led industry who to profit full of white light LED beam, had devel

15、opment large size LED flood lights chip tries to by this way reached expected target, but actually white light LED of imposed power continued over 1W above time beam instead will fell, glow efficiency is relative reduced 2030%, in other words white light LED of brightness if to than traditional LED

16、large number times, consumption power characteristics hope beyond Firefly light lamp words, on required first overcome following of four topics, including, suppression temperature rose, and ensure using life, and Improvement of luminous efficiency and photoluminescence of equalization.The problem of

17、 temperature rise of the specific method is to reduce the thermal resistance of the package; maintenance of Blue LED strip the life of a specific method, is the improvement of chip shape, small chip; improving the LED luminous efficiency of specific measures is to improve the structure, a small chip

18、 chip; improvement of luminescent characteristics of uniform methods is LED packaging methods, and in the development of these methods have come to be.Thermal problem is the fundamental way to solve packageDue to increased power instead will caused package of hot impedance sharply fell to 10K/W foll

19、owing, so abroad industry who had development resistance high temperature white light LED tries to by this improve above problem, however actually power LED panel of heat is than small power LED high dozens of times times above, and temperature rose also will makes glow efficiency sharply fell, even

20、 package technology allows high heat, but LED chip of junction temperature is has may over allowed valueFinally finally learned to solve thermal problems is the root of the package.About LED of using life, such as instead Silicon mass package material and ceramic package material, can makes LED of u

21、sing life improve one number, especially white light LED of glow spectrum contains wavelength below 450nm short wavelength light, traditional epoxy resin package material very easy is short wavelength light damage, high power white light LED of large light volume more accelerated package material of

22、 bad of, under industry who test results displayed continuous light does not to 10,000 hours, high power white light LED of brightness has reduced half above, Does not meet the basic requirements for lighting and long life.About LED of glow efficiency, improve chip structure and package structure, a

23、re can reached and low power white light LED same level, main causes is current density improve twice times above Shi, not only does not easy from large chip out light, results instead will caused glow efficiency than low power white light LED of dilemma, if improve chip of electrode constructed, th

24、eory on can solution above take light problem.Seeks to reduce the thermal resistance, improve the heat sink problemAbout luminescent characteristics of uniform, General believes that improving the concentration of fluorescent white light LED material uniformity and fluorescent technology, should be

25、able to overcome these problems. As mentioned above while improving power imposed, must try to minimize thermal impedance, improved heat dissipation, and specific content in the report are: reducing the chip to the thermal resistance of the package, contain the package thermal resistance, improve th

26、e chip to printed circuit substrate heat sink of smooth.To to reduced hot impedance, many abroad LED manufacturers will LED chip set in copper and ceramic material made of thermal fin tablets (heat sink) surface, received s then with welding way will printed circuit board Shang thermal with wire, co

27、nnection to using cooling fan forced empty cold of thermal fin tablets Shang, under Germany OSRAM Opto Semiconductors Gmb experimental results confirmed, above structure of LED chip to welding points of hot impedance can reduced 9K/W, about is traditional LED of One-sixth around, package Hou of LED

28、imposed 2W of power Shi, LED chip of junction temperature than welding points high 18K, even printed circuit board temperature rose to 500C, junction temperature at most only 700C around; phase than Xia past hot impedance once reduced words, LED chip of junction temperature on will was printed circu

29、it board temperature of effect, so then required managed to reduced LED chip of temperature, in other words reduced LED chip to welding points of hot impedance, can effective reduce LED Chip cooling burden of the job. Contrary even white light LED has suppression hot impedance of structure, if heat

30、cannot from package conduction to printed circuit board words, LED temperature rose of results glow efficiency will sharply fell, so Panasonic electrical development printed circuit board and package integration technology, the company will 1mm square of Blu-ray LED to flip chip way package in ceram

31、ic base board Shang, received s then will ceramic base board paste in copper mass printed circuit board surface, under Panasonic said contains printed circuit board zainei module overall of hot impedance about is About 15K/W.Show thermal design powerDue to thermal fin tablets and printed circuit boa

32、rd Zhijian of key s sexual directly around hot conduction effect, so printed circuit board of design became very complex, has prison Yu this United States Lumileds and Japan CITIZEN, lighting device, and LED package manufacturers, have development high power LED with simple thermal technology, CITIZ

33、EN in 2004 began samples shipments of white light LED package, does not needs special junction technology also to will thick about 23mm thermal fin tablets of heat directly emissions to external, under the CITIZEN said although the LED chip junction to heat thermal impedance than the OSRAM 9K/W fin 30K/W