Advantages and best solutions for high-power LED lighting applications

In recent years, with the continuous deepening of research on semiconductor luminescent materials, the continuous improvement of high-power LED manufacturing technology and the development and application of new materials (nitride crystals and phosphors), ultra-high brightness high-power LEDs of various colors have made breakthrough progress, and their luminous efficiency has been rapidly improved. In terms of chromaticity, all colors in the visible light band have been achieved. The most important of these is the emergence of ultra-high brightness high-power LEDs, which makes it possible for high-power LED applications to leapfrog to the high-efficiency lighting source market. High-power LED lighting is about to lead the leapfrog revolution of the fourth generation of light sources in the future.

1. Performance characteristics of high-power LEDs used as light sources for lamps

1. High luminous efficiency: After decades of development, the luminous efficiency of high-power LEDs has been greatly improved. Incandescent lamps and halogen tungsten lamps have a luminous efficiency of 12-24 lumens /watt, fluorescent lamps have a luminous efficiency of 50-70 lumens/watt, and sodium lamps have a luminous efficiency of 90-140 lumens/watt. Most of the power consumption is lost as heat. After improvement, the luminous efficiency of high-power LEDs can reach 50-200 lumens/watt, and the light has good monochromaticity and a narrow spectrum, and can directly emit colored visible light without filtering.

2. Low power consumption and energy saving: high-power LED is driven by low current and works at low voltage. Under the same lighting effect, the power consumption is one-tenth of incandescent bulbs and one-half of fluorescent tubes.

3. Long service life: The lamp with high-power LED light source is small in size and light in weight. The high-power LED light source is epoxy resin encapsulated, which can withstand high-intensity mechanical shock and vibration and is not easy to break. The average life span is 100,000 hours. The service life of high-power LED lamps can reach 5 to 10 years, which can greatly reduce the maintenance cost of lamps and avoid the pain of frequent lamp replacement.

4. Safety and environmental protection: low heat generation, no thermal radiation, low voltage operation, cold light source , can be used in some special occasions; no harmful metal mercury, no infrared and ultraviolet radiation.

5. Small size and power , flexible design: lamps with different structural shapes can be designed by combining different numbers of high-power LEDs according to different usage environments.

6. Easy to match light: soft light color, no glare; different wavelengths produce different colored lights, bright and saturated, no filter required, and different colors can be made when high-power LED is packaged to achieve the actual lighting effect.

The color of the high-pressure sodium lamp currently used is yellow, and the color temperature and image rendering index are relatively low. The image rendering index of sunlight is 100, while the image rendering index of high-pressure sodium lamps is only about 20 (yellow light); the color temperature of high-power LED light source lighting can be flexibly selected between 4000-7000K, the image rendering index can reach more than 80, and the color of the lamp is closer to natural light.

7. Large initial investment: Due to the limitations of packaging technology, high-power LED light sources are more expensive than traditional light sources, but the investment in the light source can be recovered with one year's energy saving, thus obtaining several times the net energy saving benefits every year for 4 to 9 years.

2. Several typical high-power LED application solutions:

At present, flashlights and miner's lamps using white light high-power LED as light source have been widely and ideally applied and have formed a large-scale market. Many lamp manufacturers are using different design schemes to play their respective advantages, hoping to make breakthroughs in white light high-power LED light sources in tunnel lamps, street lamps, etc. The following three schemes are currently widely used:

1. Multiple low-power bracket high-power LED type: When designing lamps, multiple bracket-type low-power Φ5~Φ10 white light high-power LEDs are used as light sources. Currently, 1~5W bulbs, 15~20W tube lamps, and 40~60W street lamps and ground lamps on the market use this solution. Generally, dozens to hundreds of Φ5~Φ10 white light high-power LEDs are used, arranged in an array, and the power supply drive can be achieved by capacitor voltage reduction. There is no need to consider too much in the design, there is no heat dissipation problem, and the structure is easy to implement; but the production process is complex, the reliability is poor, the failure rate is high, the shell size is large, and if it is made into large lamps such as street lamps, the brightness is not ideal.

2. High-power LED base type: In some public lighting, such as street lights and tunnel lights, several or even multiple high-power LED base types can be used as the light source of the lamp. This design idea has greater flexibility in the design of the optical part of the lamp, but it is more targeted for different lamps.

High-power LED light sources are point light sources with a light intensity distribution similar to that of Lambertian sources. If we simply gather high-power LED light sources for road lighting, we cannot truly take advantage of the advantages of high-power LED cold light sources. This can only be achieved through optical design. Since the current high-power LED emitting angle is limited, the maximum half-intensity angle can only reach 120 degrees. After combining multiple LEDs, although the illumination can meet the requirements, it cannot meet the uniformity requirements of national lighting standards. Through theoretical analysis, it is difficult to achieve uniform light distribution. In addition, the straightness of high-power LED light sources is difficult to achieve even through optical designs such as lenses .

If this type of lamp is designed without a reflector, part of the direct light will inevitably be wasted. Even if the reflector is designed to adjust the angle, the light band will always exist after reflection, which is also the main obstacle to its application.

The lamps using this solution can use a switch constant current drive circuit for power drive, which has a high efficiency of up to 80%. However, the lamps must have a good heat dissipation structure to ensure the service life of the lamps.

The price of lamps using pedestal high-power LED as light source is much higher than that of incandescent lamps, fluorescent lamps and energy-saving lamps, but its energy-saving effect and life span are much higher than other lamps. If used in street lamps, its one-time investment is higher, but the long-term power-saving effect and economy are worth looking forward to.

3. Single or several multi-chip integrated

Multi-chip integrated white light high-power LEDs have unique advantages: through different series and parallel combinations, a variety of rated voltages and currents can be achieved, better adapting to driver design, improving overall luminous efficacy, and reducing costs; the number of chips per unit area can be more or less, and can be packaged into a variety of different point and surface light sources.

The installation process of this type of lamp is simple, but the secondary optical design is difficult due to the multi-point light emission. Since a single chip can generally produce 20W or even 200W, the heat dissipation requirements of the lamp are also relatively stringent. The lamp design is not very flexible and is greatly limited by the chip.

Since high-power LED chips have not been domestically produced so far, they are imported from foreign countries or Taiwan, and the price is very high. However, low-power chips are in sufficient supply in China, and their price is relatively low when combined into the same power. Therefore, by packaging multiple low-power chips into an integrated white light high-power LED, it has a price advantage when used as a light source for lamps.

3. Conclusion:

Through a simple analysis of the current applications of several high-power LED light sources, it can be seen that as a new technology, the use of high-power LED light sources in urban road lighting systems still has many difficulties in application. In order to make high-power LED lighting systems meet road lighting requirements, the most critical thing is the design of the relevant optical system, that is, to achieve uniform illumination over a large area to meet the requirements of national standards.

At the same time, it makes us realize that in order to widely apply high-power LEDs to the field of lighting, in addition to optimizing the optics and structure of lamps, it is more important to improve the two major problems of optics and heat dissipation faced in the design of lighting fixtures through high-power LED research and development units, so as to jointly promote the healthy and stable development of my country's high-power LED lighting industry.