Since white LEDs have many significant advantages, there are many advantages to applying them to alternative lighting sources in public urban lighting installations. However, in order to truly give full play to the advantages of semiconductor light sources, the design of secondary optical systems is crucial. This paper introduces a unique secondary optical system for urban road lighting. It can better meet the relevant standards of urban road lighting, and can be flexibly applied to different road conditions.
Public city lighting has a large share in the lighting market. According to statistics, urban public lighting accounts for 30% of China's lighting power consumption, about 43.9 billion kwh, calculated at an average electricity price of 0.65 yuan/kwh, and annual expenditure is 28.5 billion yuan. . At present, high-pressure sodium lamps are widely used in urban public lighting. Especially on the main road, high-pressure sodium lamps can provide luminous efficiency of more than 100 lm/W. But its own shortcomings are also obvious:
The spectral composition of the light source is yellowish and the color rendering index is extremely low;
The life of the luminaire is short and the replacement work is large;
Inconvenient to adjust the power of the lamp;
With the rapid development of solid state physics in the 1990s and the breakthrough discovery of new semiconductor materials, LED technology has made rapid progress in the past 10 years. The appearance of white LED is driven by its unique low voltage, small size, light weight, good color rendering, good dimming performance, long life (up to 20,000 hours), vibration resistance, non-damage, and environmental protection requirements. So that the semiconductor light source will become an ideal energy-saving light source for urban road lighting. Its remarkable advantages are: high luminous efficiency.
At present, the commercial white LED light efficiency has reached 90-100lm/W, and it is expected to reach 150lm/W or more in two years. This is not the upper limit of LED light efficiency. Experts from all countries have set the goal of light efficiency at 200lm/W. about.
The ideal life expectancy is 100,000 hours, and the current commercial white LED life can reach 50,000 hours, which is 10 to 20 times longer than the traditional light source. When the city road lighting source is made, the light source can be replaced for 10 years, which greatly saves daily maintenance costs. It is convenient to adjust the power of the lamp intelligently; the secondary optical system can be added to make maximum use of the light energy of the LED to meet the specific illumination and light intensity distribution of various applications. In recent years, conventional fossil fuels have become increasingly tense. The prices of conventional energy such as oil and coal have been rising, and the international oil prices have reached historical highs, causing the situation of energy supply to become more severe. Due to these significant advantages of LED and the maturity of white LED technology, it is of great significance to develop an efficient, long-life, green and environmentally friendly semiconductor light source urban road lighting system.
2 Design of secondary optical system The road lighting system is different from the general lighting fixture, and its illuminated field is a rectangular area. Table 1-1 and Table 1-2 are national street lamp standards. According to the national highway lighting standard, the average illuminance of the main road is 15lx, the uniformity is 30%; the average illuminance of the secondary road is 8lx, and the uniformity is 30%, wherein the uniformity is the minimum illuminance/average illuminance of the illuminated road surface.
Since the high-pressure sodium lamp is a 360-degree full-angle illumination, a reflective device is usually added to the back of the light source to illuminate the emitted light to improve energy utilization. However, due to the large size of the high-pressure sodium lamp source and the lack of effective optical devices, the spot formed by the high-pressure sodium lamp on the road surface is usually a non-uniform spot: the center is very bright and the radial attenuation is fast. As shown in Figure 1.
In order to meet the uniformity requirements of national lighting standards, it is usually necessary to increase the output power so that the illumination of the surrounding dark spots is not less than 5 lx, and the secondary trunk is not less than 2.4 lx. However, a large amount of energy is wasted at the center and the road directly below the street lamp. The outside, which reduces the overall energy utilization.
The existing LED illumination source is a point source with a light intensity distribution approximating the Lambertian source. The individual powers are all about 1 watt, and the road illumination often requires a specific shape of the illuminated field. For example, the illumination area of ​​the main road light is specified by the state. A rectangular area of ​​10x50 square meters. Therefore, to form a road lighting system, it is not possible to simply combine the LEDs together. The circular light field thus formed will be detrimental to the utilization of light energy, and cannot meet the requirements of national standards for the uniformity of illumination of the entire illuminated area. If the light emitted by the LED chip can be reasonably distributed on the road surface and a rectangular area with uniform illumination is formed on the road surface, the energy utilization rate higher than that of the high pressure sodium lamp can be achieved with low luminous efficiency.
Below we estimate the light efficiency of different street lamps from the perspective of system efficiency. As can be seen from Table 2, the system efficiency of LED light sources is much higher than that of traditional sodium lamps.
There are also many manufacturers of various types of road lighting in China. At present, in the field of high-power LED road lighting, some factories have begun to develop, but if it is simple to carry out multi-chip or multi-device combination, it is difficult to reach the country in terms of actual illumination area and illuminance unevenness of effective area. Relevant standards. It is impossible to apply the LED street lamp to the branch road lighting and the secondary road lighting to expand into the main road lighting field. If the power is increased to meet the standard, the high luminous efficiency of the LED will no longer exist.
To design an efficient optical system for semiconductor road lighting, the key problem is to design an effective and reliable optical system so that the light emitted by the light source is evenly distributed on the road surface, that is, to solve the problem of orderly transmission of light energy, which is non-imaging. A major research direction of optics is the design of a given illuminance distribution optical system.
Non-imaging optics is a new optical branch that has been developed in recent decades to specifically study the problem of optical energy transmission. It mainly improves the energy transmission efficiency by designing an optical system that refracts and reflects the surface "orderly" to control light.
Under the approximate condition of the point source, the solution of the above given illuminance distribution problem can be abstracted into a mathematical model. However, when considering this problem in three-dimensional space, the problem becomes a very complicated second-order nonlinear Monte-amperient partial differential equation. Various methods have been studied to study the solution of this equation [6][7]. Because the solution process is very complicated, the solution obtained under certain boundary conditions is not of practical value, and a practical optical system cannot be obtained.
Our research provides a new solution and theoretical basis for solving the problem of given illumination in non-imaging optics. It can more easily apply non-imaging optics to the design of optical systems in the field of semiconductor illumination, which can better collect and utilize light sources. The large-angle light can better explore the potential of LED, and accordingly design a new LED road lighting system, improve the light efficiency of the system, and form an autonomous property. The new theory and method will also be applicable to non-imaging optical system design in other semiconductor lighting applications, such as new automotive lights, projector light sources, and backlight illumination design using LEDs as light sources.
Therefore, by improving the structure of road lighting to improve transmission efficiency, there is a large room for improvement. A more practical method is to design a special optical system using the principle of non-imaging optics to distribute the light energy emitted by the LED more reasonably, and to improve the road lighting system under the premise of meeting the requirements of national standards for illumination and uniformity. Performance, try to improve energy utilization.
3. In the theoretical research, the design of new street lamps mainly solves the difficulties of three-dimensional non-imaging optical design in the secondary optical design of semiconductor light sources, fills the gaps in this field at home and abroad, and can develop urban roads with independent intellectual property rights. Lighting applications. It has many advantages that are unmatched by other similar products:
The illuminance distribution shape is reasonable:
According to the single LED design secondary optical system, the illuminance distribution is shown in Figure 3. Since the illumination shape is a rectangle, it can be easily spliced ​​into a bright road without blind spots, that is, under the premise of meeting the national road lighting standards. Reasonably allocate energy to the road surface, effectively reducing the wasted energy.
High uniformity, high efficiency:
Another advantage of the new street lamp is that it has high illumination uniformity in the illumination area, and the uniformity is better than the national standard for street lighting, so that the road surface can be reduced to the same human eye. The illuminance requirements further save energy.
Flexible to use and easy to install:
At present, the luminous efficiency of high-power LEDs has reached 90lm/w, but a single LED can not meet the needs of road lighting, so it is necessary to assemble multiple LEDs into a practical street lamp. Since each LED can form a uniform illuminance distribution in the entire rectangular illumination area, the number of LEDs can be simply changed according to the actual road surface illumination requirements and the height of the lamp post without changing the optical system, and has a high use. flexibility.
* Stable and reliable Figure 4 is the change of uniformity of illumination of the light source measured by the high-pressure sodium lamp LED street lamp within three days. It can be clearly seen that the LED street lamp is not only in space, but also in time and evenly stable than the high-pressure sodium lamp. many.
* Long service life From the conclusion of the current light decay test, continuous lighting for 5000 hours, basically no light decay, so the LED street light to achieve 3-5 million hours of service life is fully achievable.
4. Conclusions Over the years, LED street lamps have been developed and converted into products. Many problems have been encountered and solved. Schools and enterprises have registered 50 invention and utility model patents. On this basis, the only manufacturer of large-scale mass production of LED street lamps in China has been built. It has many application cases and the actual installation has exceeded 200 kilometers. LED street light products have been applied on the road for more than a year, and have made six major product improvements, and the products are becoming more mature. The experience of product development and engineering applications accumulated in solving problems can help users understand the true characteristics of semiconductor lighting products, increase confidence in selection, and reduce political and technical risks.
As a new technology, semiconductor light source urban road lighting system has many problems in application. The most important thing is to ensure the high efficiency of the system under the premise of meeting the requirements of national standards. As conventional fossil fuels become increasingly tense, the prices of conventional energy such as oil and coal continue to rise, and the international oil prices have reached historical highs, causing the situation of energy supply to become more severe. Due to the significant advantages of LED light source and the maturity of white LED technology, the application of energy-saving, long-life, uniform illumination, flexible and convenient, green and environmentally friendly semiconductor light source urban road lighting system saves construction funds, reduces power consumption conflicts, and builds economical Society is of great significance.
Digital Water Meter,Prepaid Smart Water Meter,Brass Prepaid Smart Water Meter
Transformer Electric Energy Meter Co., Ltd. , http://www.nswatermeter.com