Application prospect of LED light source in architectural lighting

0 Preface

Since the industrial revolution, the heat-absorbing greenhouse gases such as carbon dioxide emitted by humans into the atmosphere have increased year by year, and the greenhouse effect of the atmosphere has also intensified, causing a series of serious problems such as global warming. In addition, the world energy crisis has gradually increased. Energy conservation and environmental protection has become an important issue that all human beings must face.

According to the statistics of the United Nations Global Green Energy Conservation Committee at the end of 2010, the global lighting power consumption is 20% of the total electricity consumption for the whole year, but only 10% of the electricity is converted into light energy, and 90% of the electricity is wasted. If it can effectively improve the luminous efficiency ratio of the luminaire, it will undoubtedly become an important step in energy conservation and environmental protection measures. At present, the types of low-energy, high-efficiency light sources are mainly three-color fluorescent lamps, metal halide lamps, metal sodium lamps, cold cathode tubes and LEDs, among which fluorescent lamps and metal halide lamps have been widely used. As a rising star, LED has its unique advantages and prospects in terms of energy efficiency and application breadth.

At the beginning of the invention of LED, it was only used as an indicator light source for instrumentation. Later, LEDs of various light colors were widely used in traffic lights and large-area displays, which produced good economic and social benefits. Take the 12-inch red traffic light as an example. In the United States, a long-life, low-efficiency 140 W incandescent lamp was used as the light source. It produced 2 000 lm of white light through the red filter, and the light loss was 90%. Under 200 lm of red light. In the newly designed traffic light, 18 red LED light sources, including circuit losses, consume a total of 14 W, which can produce the same light effect.

After entering 2010, the LED market has shown an explosive trend, and the LED lighting industry has a hot spot. Cree technology breakthrough, ten cities and millions of projects, Shanghai World Expo 1 billion LEDs, Guangzhou Asian Games bright project ⋯⋯ 2011, LED market continues to develop rapidly, the market potential is quite large.

1 LED light source introduction

1.1 LED development history

The world's first commercial light-emitting diode (LED) was made from tantalum in 1965 and is priced at $45. Soon after, Monsanto and Hewlett-Packard also introduced commercial LEDs made of GaAsP materials. These early red LEDs provide approximately 0.1 lm of output light per W, which is 100 times lower than the 15 lm of a typical 60-100 W incandescent lamp.

But in the next 30 years, LEDs have developed rapidly. In the early 1970s, LEDs reached 1 lm/W and the colors expanded to red, green and yellow. The successful development of white LEDs in 1998 has made LED applications a substantial step from the simple identification display function to the lighting function. As of 2010. The luminous efficiency of LED light sources in the laboratory has reached 200lm/W.

1.2 LED structure and lighting principle

LED (Light Emitting Diode) is a solid-state semiconductor device that directly converts electricity into light. The core of the LED is a semiconductor wafer. The semiconductor wafer consists of two parts, one is a P-type semiconductor and the other is an N-type semiconductor. When the two semiconductors are connected, a P-N junction is formed. When a current is applied to the wafer, electrons are pushed from the N region to the P region where electrons recombine with the holes and emit energy in the form of photons. The wavelength of light, which is the color of light, is determined by the material that forms the P-N junction. By adding different materials to the P-N junction, LEDs of three colors of red, green and blue can be produced. By adjusting the mixing ratio of the three colors, white light of various colors in the range of color temperature of 3,500 to 10,000 K can be obtained.

2 LED light source application prospects in architectural lighting

With the gradual improvement of the luminous efficacy of LED lamps and the birth of white LEDs, the conditions for the transition of LEDs from the original signal indicating light source to the lighting source are slowly maturing. Through the organic combination with intelligent control systems, LEDs are very large in various fields. Application prospects. Table 1 lists the comparison of LEDs with several common sources.

2.1 LED application prospects in residential building lighting

With the rapid development of the national economy and science and technology, people's lighting requirements inside the house are no longer limited to the level of illuminance. Energy-saving levels, light source colors and lamp shapes have become important factors for people to consider during interior decoration. LED has a tendency to replace traditional incandescent and energy-saving lamps due to its unique illumination principle and its current mature research technology.

Due to the need of energy conservation and emission reduction, incandescent lamps that have been used by humans for more than 100 years are gradually fading out of people's vision. Energy-saving lamps based on gas discharge lamps have become the first choice. It has the characteristics of low price and energy saving, but due to the use of mercury, it still has a negative side to environmental protection. Compared with traditional energy-saving lamps, LEDs have a higher luminous efficiency ratio. If the cost of LEDs can be solved, the application of LEDs in indoor lighting will be more extensive.

Table 1 Comparison of parameters between traditional light source and LED light source

In addition, by changing the material of the P-N junction, the manufacturer can easily change the illuminating color of the luminaire, which is more energy-efficient than the ordinary luminaire plus the color hood. In addition, the LED light source is small in size and can be installed not only in The indoor roof can also be embedded in the facades such as walls and floors to form a three-dimensional light environment, giving people different color and space experiences. Take a decorative lighting of a vase as an example: First of all, LED energy saving is very good, only a few watts of power can meet the multi-angle, multi-color rendering effect; secondly, the LED is small, with a high degree of concealment, can let The observer "only sees its light, not seeing its lights." At the same time, the smaller volume can reduce the difficulty of packaging, improve the level of protection, and further improve the application range of LEDs, so that LED lamps can also be applied to environments with high humidity and dust in bathrooms, kitchens, etc.

2.2 LED application prospects in public building lighting

Currently, public building design is more focused on energy-saving technologies and external landscape lighting than other buildings when considering architectural lighting solutions. In the traditional program. The indoor lighting of public buildings mainly uses T5 tube fluorescent lamps. Because T5 tube fluorescent lamps have the advantages of high luminous efficiency, low price and high uniformity of illumination, the author also carefully compares the parameters of ordinary fluorescent lamps and LED fluorescent lamps on the market. LED fluorescent lamps have no obvious advantages in terms of energy saving. At the same time, LED lamps have disadvantages in terms of color rendering and cost due to the principle of LED light source illumination. However, after years of development, LED technology has become relatively mature, so the use of LED light sources in some places with special requirements has become a new choice.

For example, shadowless lights are often used in hospital buildings. The basic principle of a shadowless lamp is to reduce the visual impact of light and shadow on the operator by increasing the number of light sources. Although the increase of the light source causes an increase in the number of light and shadow, it also weakens the darkness of each light and shadow, so that the illuminance observed from any angle can meet the surgical requirements. And so on, if you increase the number of point sources infinitely to make them close to a surface source, then in theory, the effect of the shadow can be basically eliminated, so that the illumination of any angle of view of the operator is basically the same, thus providing for surgical lighting. Guarantee. Due to the volume limitation, other light sources other than LEDs cannot meet the requirements. However, the current color rendering of LED light sources is poor, and it is not suitable for use in places with high color rendering requirements.

At present, color LED strips, color LED tubes and LED floodlights have been widely used in landscape lighting outside buildings. The LED light source is small in size, so it can be connected in series to form a lamp strip or a lamp tube. At the same time, since the LED lamp itself can emit various colors of light, the LED lamp has a unique advantage in the exterior landscape lighting of the building, especially the facade lighting. Advantage. The most classic examples of engineering are the pavilions of the Shanghai World Expo and the Guangzhou TV Tower.

The 2010 Shanghai World Expo became an LED show, and the Expo Park has also become an LED demonstration zone. Most people may not be aware of the information screens that are scattered throughout the park, the indoor lighting in each venue, the large beveled color screen on the outer wall of the oil museum, the super-large background display at the opening ceremony of the Expo, and even the country. LED grid technology is the signature of the grid museum - 720 ° hexahedron "magic box". A total of 1.05 billion LED chips were used in the Expo Park to jointly create a night view of the Expo Park. Almost every pavilion uses LED light source for exterior night lighting: the blessing sky lantern on the lighting platform of the Taiwan Pavilion, the lighting of the exterior of the Finnish pavilion with a 91 m wide and 47 m wide "moon boat" building. The LED lights are adorned with a huge curling light and shadows to create a dreamlike effect that makes people forget to return.

The 2010 Guangzhou Asian Games is undoubtedly the epoch-making application of LED in domestic outdoor LED floodlighting. Take the Guangzhou TV Tower as an example. A total of 6696 sets of 55 W LED lamps and 44 sets of 300 W LED floodlights are used. The colors of the TV towers are radiant and dazzling, but the power per m2 facade is only 5 W. More than half of the energy savings of traditional lighting solutions, only 1/3 of the national standard. In terms of aesthetics, the biggest feature of Guangzhou Tower LED lighting is the use of LED floodlighting method, that is, the lamps are installed on the back side of the column to brighten the column, forming a silhouette effect, while using the rich characteristics of LED to highlight the dynamic lines of the Guangzhou Tower. The latest LED chip technology not only makes the Guangzhou TV Tower show a million-level infinite color, but also greatly reduces the operating cost of this large-scale nightscape lighting. It is roughly estimated that the power consumption per hour is less than 1,000 yuan. For such a large-scale night lighting, the cost is very low.

2.3 LED application prospects in landscape lighting

Commonly used lights for landscape lighting are: garden lights, street lights, lawn lights, buried lights and underwater lights. With the development of LED technology, lawn lights, buried lights and pool lights have begun to use a large number of LED light sources. Compared with the previous lamps, the new LED lamps are smaller in size and higher in power factor, and have obvious advantages in terms of energy saving and protection level.

a. Lawn lights and buried lights. Lawn lights and buried lights are often used for landscaping lighting in parks or urban green belts. Traditional lamps mainly use metal halide lamps, high-pressure sodium lamps or energy-saving lamps. The rated power is generally 18-70 W. If LED light source is used, only 5- 10 W can achieve similar results, and because of the small size of LED light-emitting diodes, the size of the luminaire can be effectively reduced. At the same time, the smaller volume of the light source facilitates the versatility of the shape of the luminaire, which also expands the range of application of the LED.

b. Underwater lights. The underwater light is mainly used for floodlighting near the water surface or below the water surface. It is used in parks, squares, swimming pools and fountain pools. It is a type of lamps that require high energy conservation and protection levels. For safety reasons, underwater lights often use 12 V power supply below the human body safety voltage limit, so that under the same power conditions, the rated current at the safe voltage will be much higher than the rated current at the power frequency voltage. Ensure that the line voltage drop and cable temperature rise meet the requirements, and the cable cross section will increase accordingly. At this time, if a lamp with a smaller power is used, not only the energy saving effect can be achieved, but also the investment in the cable can be largely saved. Conventional underwater lights often use incandescent or metal halide lamps, and the rated power is generally 50-80w. If an LED light source is used, only 6~10 W can be used to achieve similar effects. The LED light source digital control system is used in the fountain pool, and it can cooperate with the fountain control system to achieve the visual effect of the intersection.

c. Street lights and garden lights. Since the technology of LED in high-power lighting is not very mature, the application in streetlights and garden lights is not widely used. At the same time, due to the large initial investment of high-power LED street lamps, it has become a reason for restricting the development of LEDs in the direction of street lamps. . However, with the gradual maturity of technology, it is only a matter of time to believe that LEDs are widely used in street lamps.

3 LED light source limitations and deficiencies

Although LED light sources have various advantages over traditional light sources, there are still some technical problems that have not yet been solved:

a. The cost is higher. In practical engineering, cost is often an important issue that people pay attention to. In the case of similar functions, the cost will directly determine the fate of the product. LED lamps are not perfect due to the manufacturing process, and the LEDs generate a lot of heat. The need for an aluminum lamp housing is significantly higher than the most widely used gas discharge lamps, which makes LEDs less competitive in some traditional lighting applications.

b. Poor color rendering. At present, white LEDs generally use a blue-emitting LED to superimpose a yellow-emitting yttrium aluminum garnet (YAG) phosphor excited by blue light to synthesize white light. Since the luminescence spectrum contains only two main waves of blue and yellow, there is a problem that the color temperature is high and the color rendering index is low.

c. Light decay problem. Since the illumination source has higher brightness requirements than the display light source, the white LED power should be as large as possible. When the current is high, the ignition time increases, the LED's own light decay and the phosphor and packaging materials deteriorate. The light pass is reduced, and the life of the white LED is greatly shortened.

d. The heat is large. Since the surface area of ​​the LED chip is less than 1 mm2, the current density is high during operation, and the diode heat is severe. If the heat is not dissipated, the chip will be damaged. Because the illumination requires multiple LEDs combined, the LED density is large, and the illumination temperature is long. It is inevitable that it will be lifted, so heat dissipation must be strengthened, which makes the volume of the LED light source larger, making it more difficult to design the shape of the lamp.

4 Conclusion

According to a large number of application examples of LED lamps, we can roughly see the application prospects of LED lamps. It is believed that with the continuous advancement of technology and the continuous improvement of manufacturing processes, the era of large-scale application of LED lamps in various fields will come.

Edit: Cedar