The Luminescence Performance of High-power LED had already been known by people along with the recession of time and temperature. It is an important problem that LED lighting current faces. Owing to the price of High-power LED is fairly high, if you want to gain better ROI that compares to other light source, you must make up the high price of lamps and lanterns by long-life and saving electric charge. Now High-power LED in domestic solves light failure problem (Light Attenuation Measurement), its usual method is that lamps and lanterns offer light quantity exceeding need before they reach to life expectancy. Light quantity reduces step by step during the using process of lamps and lanterns; it approaches the actual demand value when lamps and lanterns reach to life expectancy. Although this way is simple, it wastes electric energy. Excessive lighting also affects life time of lights, so it is very significant to find better solution for light failure.
From normal using of LED to see, the leading factor that affects lifetime of LED is heat. The main source of heat is the hot that LED creates. High-power LED transforms 20%-30% of electric energy to light; more than 70% of electric energy has been transformed into heat. Moreover, if driver uses the method of building-in, the wastage of driver also adds the heat of LED. The accumulation of heat makes the temperature rise, the rising of temperature causes the performance of chips decay, material ageing, and degeneration.
The light failure of High-power LED is mainly determined by chip itself. In addition, misapplication(improper power supply, cooling bad) is also the factor of leading to light failure.
The light failure of LED is relevant to TJ. TJ is the temperature of semiconductor PN junction (LED Junction Temperature Measurement). The earlier and higher the TJ appears, the shorter the lifetime is. We can see that if TJ is 105 degree, when luminance reduces to 70%, lifetime only has more than 10000 hours, lifetime is more than 2000 hours when TJ is 95 degree. But TJ has been reduced to 75 degree, lifetime have 4000 hours, lifetime can extends to 9000 hours when TJ is 65 degree. So the very pivotal point of extending lifetime is reducing TJ. But in fact, owning to body size and cost control of lights themselves, the TJ of LED is more difficult to control in a relatively low value. Light failure is a problem of LED lighting designing. As for a piece of specific LED chip, traditional scheme sets the output current in a value of needing that fulfills the lumen that the lifetime of LED light source can reach. This can make lumen (Luminous Flux Meter) value of LED exporting been used in above rated 130% or higher.
So the traditional lighting designing of LED is always in excessive lighting state. For a new light, excessive lighting may reach to more than 30%. But capacity decay compensation can make lights constant in light quantity that users need in life cycle. Saving the wasting energy of excessive lighting also extends the lifetime of light source and driver.
First, we need to get characteristic curve of light decay from the datasheet of LED chip in line with the temperature of LED chip, then set up mathematical model. LED driver (LED Driver Tester) can control current that itself exports along with the magnifying LED light adding lighting time, and then realize the increasing light quantity of LED light source exporting along with adding lighting time, then realize light decay, thus guarantee light quantity in a needing value along with adding lighting time. Pilot basic block diagram.
Light decay compensation includes a compensation design unit, a timing control unit and an output unit. This can make the output current of driver change along with designing of controller. But it can set different compensation curve by using external Rest.
For those existing LED drivers without built-in light failure compensation, so long as the driver is dimmed at 0-10v, it can realize light decay by outlay compensation controller of light decay, specific realization way.
Comparing with the method of existing light decay compensation in early stage, this technology of light decay needn’t obligate current when it drives LED source, so as to save energy and extend the lifetime of lamps. It can reduce cost if designing is rational. This method makes the same LED driving device realize different light failure compensation characteristic, and enhances generality of device. In addition, Lisun can read in customized program in a controller for clients before products leave factory. But in the near future, this compensation controller of light decay can integrate to controller which will have other functions, and realize LED controlling which is more multifunctional.