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Early Led Tube Only Flashlightsis no exception, there is a certain life. Early Led Tube only flashlights, lamp kind of gift, with not a long time, life problems are not prominent. But now Led Tube already widely used in outdoor and indoor lighting, especially, is a high-power Led Tube lights, its power, high fever, long working hours, life is very prominent problem. Led Tube in the past that life is 10 million hours must seem completely shattered the myth. So in the end the problem lie? If we do not consider the power and drive failure, Led Tube life performance of its lumen, which is a long time, the brightness is getting dark, until the last out. Attenuation is usually defined as 30% of the time life. So Led Tube life can predict it? No simple answer to this question, you need to start early. 1, Led Tube light decline Most white Led Tube Led Tube light from blue and yellow phosphor obtained. Led Tube light failure caused by two main reasons, one is light blue Led Tube itself bad, bad blue Led Tube light than red, yellow, green Led Tube faster. There is also a bad light is a phosphor, the phosphor decay at high temperatures is very serious. Various brands of Led Tube light of its failure is different. Led Tube manufacturers are usually able to give a standard curve of light decline. Cree's light like the United States to decline curve shown in Figure 1. Figure 1. Cree's Led Tube light decay curve It can be seen from the figure, Led Tube light failure and its junction temperature is related to the so-called PN junction semiconductor junction temperature is the temperature, the higher the junction temperature light failure occurred earlier, that is, the shorter life expectancy. It can be seen from the chart, if the junction temperature of 105 degrees, brightness to 70% of the life expectancy of over ten thousand hours, 95 degrees there is 20,000 hours, while the junction temperature cools to 75 degrees, the life there are 5 million hours of 65 degrees can also be extended to 90,000 hours. So the key to longevity is to reduce the junction temperature. However, these data only for the Cree of Led Tube. Not suitable for other companies Led Tube. For example, the company's LuxeonK2 LumiLed Tube light decay curve is shown in Figure 2. Figure 2. LumiLed Tube Company LuxeonK2 light decay curve When the junction temperature increase from 115 to 135 , it will cause reduced life expectancy from 50,000 hours to 20,000 hours. Other bad light curve of each company should be able to obtain a copy of the original. 2, How can extend the life of Led Tube Can be concluded from the figure, to extend its life, the key is to reduce the junction temperature. The key to reducing the junction temperature is to have a good heat sink. Led Tube in time to put out the thermal distribution. Here we are not prepared to discuss how to design a heat sink, but rather to discuss a radiator cooling effect which is relatively good question. In fact, this is a junction temperature of the measurement problem, if we are able to measure any kind of heat sink the junction temperature can be achieved, then not only compare the radiator cooling effect, but also know that after using this radiator Led Tube life can achieve. 3, how to measure the junction temperature Junction temperature measurement appears to be a temperature problem, but to measure the junction temperature within the Led Tube, can not get into a PN junction thermometer or thermocouple to measure its temperature. Of course it can still shell temperature measurement using thermocouples, and then gives the thermal resistance Rjc (junction to case), it can calculate the junction temperature. However, after the radiator is installed, the problem has become complicated again. Because usually Led Tube is welded to the aluminum plate, and aluminum plate and installed the radiator, if the only measure the temperature of the radiator shell, then to calculate the junction temperature must know a lot of resistance values. Including Rjc (junction to case), Rcm (shell to the aluminum plate, in fact, which should also include the printed version of the thermal resistance of thin films), Rms (aluminum plate to the radiator), Rsa (radiator to the air), which as long as a data inaccuracy will affect the accuracy of the test. Figure 3 shows the various resistance Led Tube diagram to the radiator. Which combined a lot of resistance, making it a more limited accuracy. That is, the heat sink from the surface temperature measured to infer more accurate junction temperature difference. Figure 3. Led Tube to the radiator diagram of the various resistance Fortunately, there is an indirect method of measuring temperature, it is to measure voltage. Then the junction temperature and voltage on which it? How this relationship is like? We should first talk in Led Tube voltage characteristic. 4, Led Tube voltage characteristics of the temperature coefficient We know that Led Tube is a semiconductor diode, diode, like it and all have a volt-ampere characteristic, but also, and, like all of the semiconductor diode, the IV characteristics have a temperature. Its characteristics is that when the temperature is rising, and voltammetric characteristics of the left. Figure 4 drawn Led Tube voltage characteristic temperature characteristics. Figure 4. Led Tube voltage characteristics of the temperature characteristics Led Tube assumed, constant current power supply to Io, the junction temperature of T1, the voltage V1, and when the junction temperature rise for the T2, left the entire voltage characteristics, current Io constant voltage becomes V2. Is the temperature difference between the two voltage removed, the temperature coefficient can be obtained in order to mV / oC said. For ordinary silicon diode, the temperature coefficient is about -2mV/oC. However, most of Led Tube is not made of silicon materials, it should also go to the temperature coefficient of determination. Fortunately, manufacturers of various Led Tube Most of the data table given its temperature coefficient. For example, Cree's XLamp7090XR-E high-power Led Tube, the temperature coefficient of -4mV/oC. Than ordinary silicon diode 2 times larger. In the United States Puri array Led Tube (BXRA) to give a more detailed data. However, they are given the data, its scope is too large, so that the value of lost use. Anyway, just know that the temperature coefficient of Led Tube can easily measure the forward voltage Led Tube projected Led Tube in the junction temperature of the. 5, how the junction temperature measurement Led Tube Now on to Cree's XLamp7090XR-E as an example. To illustrate how the junction temperature measurement Led Tube. Led Tube requirements have been installed in the radiator, and is a constant current drive for power. Led Tube should also connected to lead them to the two lines. Previously put in the power connected to the output voltage meter (Led Tube of positive and negative), then connect the power, while Led Tube not heat up before, immediately read the voltmeter reading, which is equivalent to the value of V1, and then wait at least 1 hour, so it has reached thermal equilibrium, and then test again, Led Tube voltage across the equivalent of V2. Subtract these two values, the difference obtained. Longer be removed 4mV look to a junction temperature can be drawn. In fact, Led Tube mostly in series and then parallel to many, that does not matter, when the voltage difference is a series of Led Tube by many of the common contribution, so should the voltage difference divided by the number of tandem re-Led Tube Removal of the 4mV, you can get the junction temperature. For example, Led Tube Series 2 and 10, the first measured voltage is 33V, the second time after the heat balance of the measured voltage is 30V, the voltage difference of 3V. This number divided by the first series of Led Tube number (10), are 0.3V, divided by 4mV, can be 75 degrees. Assume that the environment before starting the temperature is 20 degrees, this time the junction temperature should be 95 degrees. Results obtained using this method temperature, certainly better than the heat sink temperature measurement using thermocouples again derive the junction temperature must be accurate lot. 6, how to predict the life of the lamp To infer from the life of the junction temperature should be as simple as check the curve in Figure 1, you can know the junction temperature of 95 degrees corresponds to the time of life can get Led Tube lifetime of 20,000 hours of. However, this method is used indoor Led Tube light there is a certain credibility, if applied to outdoor Led Tube lamps, especially high-power Led Tube lights, where there are many uncertain factors. The biggest problem is Led Tube lights radiator cooling efficiency decreases with time. This is due to dust, bird feces and makes the accumulation of heat efficiency. And because there are very strong UV outdoors, but also will reduce the life of Led Tube. UV mainly to the aging of epoxy encapsulated play a big role, if the use of silica gel, could be improved. UV aging of phosphors also have some bad effect, but not very serious. However, this method is used to compare the relative effects of the two radiator cooling is more effective. Obviously, the smaller the voltage characteristic left of the radiator, the heat, the better. In addition, indoor for predicting life expectancy of lamps or a certain accuracy. ...

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