At present, my country is creating a resource-saving and environment-friendly society, and the concept of "green lighting" is gradually gaining popularity. With the continuous advancement of science and technology and the rapid development of semiconductor material application technology, low-power LED light sources have been widely used in landscape lighting, and high-power LED street lights have attracted more and more attention from all walks of life.

The light-emitting principle of LED lights:

LED (Light Emitting Diode), a light-emitting diode, is made of III-IV compounds and is a solid-state semiconductor device that can directly convert electricity into light. The heart of LED is a semiconductor wafer, the semiconductor wafer consists of three parts, one part is a P-type semiconductor, in which holes dominate, and the other end is an N-type semiconductor. When the current acts on the wafer through the wire, the electrons and holes will be pushed into the quantum well, where the electrons and holes recombine, and then emit energy in the form of photons, which is the principle of LED light emission. The wavelength of light, which is also the color of light, is determined by the material that forms the P-N junction.

The light-emitting principle of high pressure sodium lamp:

The high-pressure sodium lamp uses an electric arc between the electrodes at both ends of the arc tube after being energized. Due to the high temperature of the arc, the sodium amalgam in the tube is heated and evaporated into mercury vapor and sodium vapor. The electrons emitted by the cathode are in the process of moving to the anode. Impact discharge The atoms of the substance can obtain energy to generate ionization or excitation, and then return to the ground state from the excited state; or change from the ionized state to the excited state, and then return to the ground state in an infinite cycle. At this time, the excess energy is released in the form of light radiation, Light is produced.

High-power LED street light is a new type of lighting method that realizes lighting needs by lighting LED groups at low DC voltage. It has the characteristics of high brightness and good color rendering; The combination of solar energy makes solar LED street lights a possibility for future road lighting.

1. About energy efficiency analysis and comparison

The lighting installation power of the two should be compared on the premise of reaching the same illuminance (brightness) level and close to the lighting quality standard. Due to the high luminous efficiency of high-power sodium lamps (250~400W), it can reach 130~1401m/W, while the luminous efficiency of low-power lamps (100~150W) is about 80~1001m/W. Street lights mostly use 1W LED tubes, and their light effects are similar, so it is advisable to analyze high-power street lights and low-power street lights separately.

(1) High-power (≥250W) street lamp: high-pressure sodium lamp has high efficiency, considering three factors such as ballast loss, lamp efficiency and optical channel utilization. If the comprehensive efficiency is calculated as 0.55, the effective luminous efficiency of sodium lamp is about 70~751m/W; and the effective light efficiency of LED street lamps is currently about 621m/W in the United States, and the best domestic enterprises have reached 56~581m/W. Therefore, Guzhen Runjing Street Lamp feels that for high-power street lamps, the energy efficiency of LEDs is lower than that of sodium lamps.

(2) Low-power (≤150W) street lamps: the effective luminous efficacy of sodium lamps (including the overall efficiency of 0.55) is about 45~551m/W, and LEDs are still calculated at 56~581m/W, then LEDs can save energy by 10% compared to sodium lamps. %~20%, up to 30%. From the above analysis, it can be seen that when the low power (≤150W) used for the branch circuit, the LED street lamp can save energy by 10%~30% compared with the sodium lamp, while the high power is still not comparable to the energy efficiency of the sodium lamp. Therefore, those general claims that LED street lamps are more energy-saving than high-pressure sodium lamps, and even save 50% or 60% of energy, are obviously exaggerated and hyped. We should adhere to the principle of scientific analysis and seeking truth from facts, otherwise it is easy to mislead users and the general public.

2. Analysis of the light color of the light source on the road lighting effect

The correlated color temperature (Tcp) of high-pressure sodium lamps is about 2100K, which is a warm color temperature, and its color rendering index (Ra) is only 23~25, which is low in color rendering; while the color temperature of LED street lights is more than 5300K, which is a cool color temperature, which is better. Its Ra can reach 70~80, and its color rendering is good. As the expressway and main road for motor vehicles, the sodium lamp with yellow light is slightly better than the white light in seeing the road conditions at a distance of about 90~160m in front, especially in foggy and dusty air conditions. more advantage. For sidewalks, commercial pedestrian streets, residential areas and other roads, the color rendering of LEDs is better than that of sodium lamps, and it is more advantageous to distinguish people's conditions.

3. Economic analysis and comparison

High-pressure sodium lamps, each set is about 1200~1500 yuan; at present, LED street lamps, according to the size of the power, the price varies greatly, about 4000~8000 yuan. As far as the current situation is concerned, LED street lights are obviously too expensive, and the price is as high as 3 to 5 times. As before, LEDs with less than 150W can save energy by 10%~30%, and each lamp can save about 50~150KWh of electricity every year, and it is impossible to recover the extra cost of purchasing lamps. It can only be expected that in the next few years, the development trend of LED will gradually reduce its price and further improve its energy efficiency, and then compare its economic performance.

4. Service life analysis

The comparative service life should be based on the whole lamp life. High-pressure sodium lamps include light sources, electrical accessories (mainly ballasts, triggers) and lamps. The average life of sodium lamps for street lamps is 3 to 5 years, and the energy-saving magnetic ballasts will not be less than 20 years. The same is true for lamps. However, there is no experience in the service life of LED street lamps. The existing enterprises claim to be 50,000 and 60,000 hours, and there is no reliable basis. The requirements formulated by the US Energy Star are divided into two levels of no less than 35000h and 25000h. The main reason is that the LED chip has a long life, but it has a great relationship with many factors such as temperature after packaging, heat dissipation, etc. In addition, there are also electronic drive circuit devices The life of components, such as capacitors, is often only 8000h to 10000h. So on the whole, the service life of LED street lights cannot be compared with that of sodium street lights.

5. Maintain performance comparison

Users represented by urban street lamp management departments are more concerned about the maintenance performance of street lamps. According to the analysis, the maintenance performance of the sodium lamp is good. The lamps do not need to be replaced as long as they are scrubbed. The ballast is rarely replaced, and the light source is replaced once every 3 to 5 years, which is also very convenient. For LED street lights, involving LED tubes, modules (including lenses, etc.), power supply devices, etc., there is a high possibility of damage to components and components, and maintenance and replacement are also difficult. It is likely to be replaced as a whole, and the cost is high. solve. There is no standard for LED street lights to follow, which is not good for bidding, ordering, use and maintenance. To sum up, we believe that LED street lights are a new thing that has appeared in recent years. With the development of the LED industry, there will be greater development and broad prospects. However, there are still many problems in the current application status. Although there are a few companies engaged in the research, development and production of LED street lamps, they have made great efforts to solve some technical problems and promote the advancement of the product. They are worthy of the industry's elites; But on the whole, the level, quality, and difference of LED street light products are uneven and very different. There is no standard to regulate them. Some of them are eager for quick success. , Without a reasonable light distribution of lamps, it cannot meet the requirements of promotion and use. We hope that scientific research, teaching, design units, user units and production enterprises will work together to solve various technical problems, improve product levels, formulate and improve a series of standards, and make various preparations for popularization and application. In terms of promotion and application, we should adhere to a gradual approach, starting from the pilot, sum up experience, and continuously improve; we should start with low-power LED street lights applied to branch roads and residential roads, and then develop to main roads, high-power street lights, and gradually advance. No matter what light sources and lamps are used, they should meet the requirements of "Design Standards for Urban Road Lighting" (CJJ45-2006), including brightness, illuminance, uniformity and other quality indicators. Adhere to seeking truth from facts, avoid exaggerated words, do not elevate yourself in comparison, and do not lower others, adhere to lighting quality, illumination (brightness) level, adhere to the combination of technology and economy, application and energy conservation and environmental protection, prevent excessive hype, for users Services, responsible for users, do not mislead users, and give users a true face. Don't say "replace" any light source lightly, it should take several years or years of efforts to continuously improve itself, in order to become a high-quality and efficient new light source and lamps in road lighting for users to choose. Let the user speak, let the use effect to evaluate. Luminous Efficiency: The unit is lumens per watt Lm/w. That is, the ability of an electric light source to convert electrical energy into light energy, expressed by dividing the luminous flux emitted by the power consumption.

6. Luminous efficiency

The luminous efficiency of LED light sources is currently about 75Lm/w in the United States and Japan abroad, and about 65Lm/w for domestically produced LEDs. The luminous efficiency of the high-pressure sodium light source is about 100Lm/w, and the luminous flux per w is 25-35Lm/w higher than that of the LED. The luminous efficiency of 400w high pressure sodium lamp is as high as 120Lm/w.

7. Mist permeability

In road lighting, there is a big misunderstanding about the penetration of LED street lights for fog. Most people have always believed that the penetration of LED street lights is lower than that of traditional lighting sources, sodium lamps, which is a wrong understanding. Most people see some information on the Internet or see some sensory feelings on the road, and do not do scientific evaluation and analysis, so that the light penetration of LED street lights is poor. In this article, a scientific analysis of this situation will be made.