LED lighting market opportunities bring infinite imagination to the industry, LED lighting applications have jumped from outdoor LEDs to indoor lighting applications. According to the statistics of Strategies Unlimited, the development of LED indoor lighting will have an exponential growth trend in the next five years. According to estimates, by 2011, its output value will be tens of billions of dollars. In particular, in 2009, the European Union took the lead in implementing the plan to ban incandescent lamps, and the issue of energy conservation received much attention, which created a huge market opportunity and optimistic prospects for LED indoor lighting. The following is an analysis of the development of high-power LEDs in the field of indoor lighting from the requirements of lighting technology such as heat dissipation technology, optical design and drive design.
The development of high-power LED lighting The development of high-power LED lighting depends on two elements: the chip itself; the second is the lighting technology, including heat dissipation, optics, and drive.
2, chip support
At present, the key to the development of LED chip technology lies in the substrate material and epitaxial growth technology. The base material is developed from traditional sapphire materials, silicon and silicon carbide to new materials such as zinc oxide and gallium nitride. Whether it's high-power chips for accent lighting and monolithic lighting, or low-power chips for decorative lighting and some simple auxiliary lighting, the key to technology upgrades is how to develop more efficient and stable chips. In just a few years, LEDs have achieved great breakthroughs in light efficiency with a series of technological improvements including chip structure, surface roughening and multi-quantum well structure design. Figure 1 is a schematic diagram showing the development of an LED chip structure. As production technology matures, LED quantum efficiency will further increase, and the efficacy of LED chips will also increase.
Thin-film technology is the core technology in the production of ultra-bright LED chips, which reduces the light output loss on each side and allows more than 97% of the light to be output from the front side by means of the reflective surface at the bottom (see Figure 2). This not only significantly improves the light efficiency of the LED, but also creates superior convenience for the lens design.
3, the needs of lighting technology
3.1 Heat dissipation technology
Volkswagen has always been concerned about the service life of lamps. If only relying on low thermal resistance LED components is not able to build a good heat dissipation system for the luminaire device, and it is necessary to effectively reduce the thermal resistance from the PN node to the surrounding environment, the PN junction temperature of the LED can be greatly reduced, and the successful implementation is prolonged. The life of LED luminaires and the goal of increasing actual luminous flux. Different from the traditional lamps, the printed circuit board is not only the power supply carrier of the LED, but also the heat dissipation carrier of the LED. Therefore, the heat dissipation design of the heat sink and the printed circuit board is very important. In addition, luminaire manufacturers must consider the quality, thickness and size of the heat sink material as well as the handling and connection of the heat sink interface.
3.2 Optical design
Compared with traditional luminaires, directionality and point source are the two typical characteristics of LEDs, and how to make good use of these two characteristics of LEDs is the key to the optical design of luminaires.
Through the binary optical design of LEDs, LED luminaires can achieve better light distribution curves. For example, in indoor lighting applications where the light of the luminaire needs to be very bright, a high transmittance lampshade can be used to increase light extraction efficiency. Or the application of the light guide plate technology to the luminaire, thereby changing the LED point light source to the surface light source, can not only improve the light distribution uniformity of the luminaire, but also prevent glare. In addition, in some auxiliary lighting and accent lighting applications, a specific concentrating effect is required to highlight the object to be illuminated, in which case it can be used with some concentrating lenses or reflectors to achieve the desired optical effect. .
It must be ensured that the LED drive current is a constant current output. When the LED is operating at forward current, the relative change in node voltage is very small. Therefore, ensuring a constant LED drive current is essentially equal to ensuring a constant LED output current. In addition, lighting control design is one of the mainstream drive designs today. It is mostly used in ambient lighting applications. It can achieve different brightness levels according to different environments, and can fully achieve energy-saving goals. At present, the main trend of drive design focuses on improving power factor, reducing drive power consumption, optimizing control accuracy and speeding up response. During the design process, the design of the power supply, the layout of the printed circuit board, and the series-parallel connection are all factors that must be considered.
4. Technical challenges of high power LED lighting
Even though LEDs have performed satisfactorily in indoor accent lighting and decorative lighting applications, there are still many challenges in general lighting and ambient lighting applications, including initial cost, light efficiency at lower color temperatures, color rendering index, and System reliability, etc.
4.1 Further reduce the initial cost
Cost is a relatively sensitive factor in indoor lighting, especially in home lighting applications. Despite the increasing number of LED lights and the increasing light efficiency, the problem of high prices still exists. However, when the price of the LED light source is lowered and the overall optimization of the system design, the total cost will inevitably fall. Recall that when the compact energy-saving fluorescent lamp was first put on the market, the cost was about $15, and it has now fallen below $1.50. Therefore, it can be inferred that as the market continues to develop, the price of LED lights will soon reach the level acceptable to the public.
4.2 Improve light efficiency at low color temperatures
Low color temperatures below 4,000K are often the first choice for indoor home lighting. Warm white light makes the whole environment warmer and more relaxed, while cool white light gives a clean, efficient and bright feeling, which is more suitable for office and outdoor lighting. Because of the phosphor, the efficacy of LEDs at low color temperatures is typically about 30% lower than at high color temperatures.
4.3 Management of light efficiency and color rendering index
In general, the higher the luminous efficacy of the LED, the lower the color rendering index. Indoor lighting usually requires LEDs to have a higher color rendering index in order to objectively display the brightness and color of the object and achieve the real effect when the naked eye directly observes the external landscape. To this end, while improving the LED light efficiency, it is necessary to further increase the color rendering index. Another method is to add some red light to the surface of the luminaire to achieve a color rendering index of more than 90.
4.4 Improve efficiency during high current drive
At present, the current of a 1W LED can usually be increased from 350mA to 1,000mA. However, at high currents, overall efficiency typically decreases significantly, even as the luminous flux increases. Therefore, the total cost of the system and the efficacy of the light must be balanced. If you can improve the efficacy of LEDs with high current drive, you can greatly reduce the number of LEDs required by ensuring higher system efficacy, resulting in significant cost savings.
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