Lucio Di Jasio
The writer is the application manager of Microchip Technology
In recent years, new solid-state lighting (SSL) solutions have become more energy efficient and more powerful, especially the introduction of power LEDs has caused major changes in the lighting market. LEDs are an irresistible alternative to many vertical applications such as LED lights, automotive applications and LCD TV backlighting applications. However, the widespread use of LEDs for general lighting is not an easy task, and the cost and performance of SSL solutions will undoubtedly continue to improve, and it is expected to be universally adopted in 2010.
SSL grabs the general lighting market
The problem with the new solid-state lighting turning to the general lighting market is the capacity and inertia of the market. Other high-efficiency lighting technologies have also tried to enter the general lighting market in recent years, but most have not succeeded. A new lighting technology that has to occupy a place in a complex market must overcome obstacles, and compact fluorescent lamps are an example. Its compatibility with older products may be the biggest challenge, and many who are skeptical about new solid-state lighting point out that there are significant risks in trying to directly improve the design of incandescent bulb lighting applications. Temperature management, energy conversion, and color management are all fundamental issues that must be addressed. Industry players are beginning to realize that it is necessary not only to improve traditional electromechanical solutions into more high-end electronic solutions, but also to adopt intelligent digital control methods to enjoy the benefits and cost savings of this technology.
White light discusses the focus for LED manufacturers
One of the biggest advantages of LED technology is that it can produce pure color light with extremely narrow spectrum in the form of electromagnetic radiation, and it has high efficiency and no heat radiation. If the color produced is exactly the color you want, it's great, but in general lighting applications, what we really want is "white" light. In other words, we need to mix multiple colors in precise proportions, similar to the spectrum of sunlight that reaches the human eye after filtering through the Earth's atmosphere.
Although similar to fluorescent lamps, it is possible to obtain white light from an LED source by applying a layer of phosphorous material on top of the blue or ultraviolet illuminator, but the composition of the actual phosphorous material and its thickness and coating position remain all major LEDs. The issue is widely discussed by manufacturers, and this is reflected in the fact that manufacturers announce newer and more efficient research results every month. Moreover, the quality of the generated light is also constantly increasing, and the perceived quality of the human eye is actually measured by measuring the correlated color temperature, that is, the black body temperature (CCT) which is very close to the perceived color of the lamp. This is a very important issue because the light produced by early fluorescent lamps is a bit dazzling, which has led to the “cold encounter†of early compact fluorescent lamps.
Another way to get white light from an LED is to accurately mix red, green, and blue light (RGB) from a three-color illuminator at the correct ratio so that not only white light but also the associated color temperature can be obtained. Figure 1 shows a simple application circuit that uses an 8-bit microcontroller in an eight-pin package to control the tri-color LED. The relative brightness of the three illuminators is controlled by simple software technology. Each illuminator can achieve 6-bit resolution (providing sixty-four brightness levels), which is sufficient for precise control of color output (white light) and selection of required CCT .
The PIC12HV615 flash microcontroller in the figure integrates a shunt regulator, an oscillator that provides an 8MHz clock, a reset circuit, and an analog-to-digital converter to provide a complete and flexible single-chip solution. The in-circuit programmable functionality of this flash component also allows the color calibration process to be performed at production time, providing a way to compensate for differences in performance and differences between components of various illuminators.
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