Evaluation and analysis of LED street lamps replacing traditional lighting projects

With the improvement of LED luminous efficiency and lifespan, coupled with the advantages of power saving, energy saving and environmental protection, the feasibility of LED replacing traditional lighting in street lighting has been greatly improved. With the rapid growth of LED technology and the continuous improvement of product characteristics, LED street light demonstration projects have been launched in various countries. Through the evaluation and analysis of LED street light demonstration projects, it provides a reference for governments and LED manufacturers in the future investment and application of street light market.

LED Street Light Demonstration Project - Oakland, California, USA

Take the LED street light demonstration program evaluation conducted by the U.S. Department of Energy in Oakland, California as an example. The project adopted a two-stage evaluation process. In the first stage, the research team first selected a parking lot in Oakland to conduct pre-installation and post-installation measurements , with the aim of evaluating whether LED lighting may have a negative impact on safety when actually deployed on general streets; after confirming that there is no special negative impact on local residents after the installation, the second stage is to install and evaluate on actual roads, and to conduct surveys on local residents to estimate satisfaction, acceptance, and economic costs.

This project is an evaluation of the lighting effect of LED in street lamp applications. The study is conducted on the roads in Oakland by replacing the original high-pressure sodium lamps with LED lamps . The evaluation method adopts four items for evaluation, including light source output efficiency, energy and power usage, user satisfaction survey and economic cost estimation. This evaluation project hopes that California can more quickly introduce emerging energy technologies and applications that have not yet been adopted through information such as energy savings, demand reduction, market potential, market entry barriers, gradually increasing costs and expected technology life cycle.

The purpose of this evaluation project is to evaluate the power, light source efficiency and economic performance of high pressure sodium lamps compared to LED lamps. Potential economic demand and energy savings are evaluated based on average wattage usage and estimated annual kilowatt usage; light source performance is considered in terms of illuminance , uniformity, related color temperature and satisfaction of relevant groups. Finally, economic performance is evaluated based on the simple-payback period for device replacement or replacement, lamp life, maintenance costs and electricity costs.

Compared with traditional lighting sources, LEDs provide better lighting capabilities in terms of light source dispersion and energy saving, and have changed the general industry's perception of the use of high-quality light sources. They are also used in streets and general roads. Currently, streets are illuminated by high-pressure sodium lamps, while some use metal halides, low-pressure sodium lamps or other types for lighting. The use of high-pressure sodium lamps is due to their longer service life and higher efficiency compared to other traditional lamps, but they are less selective in the color they provide. LEDs have a longer service life than high-pressure sodium lamps, lower maintenance costs, a variety of color options, lower energy consumption and cost savings. However, the initial cost of using LEDs is still higher than the commonly used light sources.

According to a report by the U.S. Department of Energy , current LED technology is changing rapidly. Overall, the luminous efficiency of LEDs improves by about 35% each year, which can reduce costs by 20%.

Where to implement the program and how to evaluate it

This LED street lamp demonstration project is to replace the original 121-watt high-pressure sodium lamp (HPS) with 15 78-watt LED lamps on the Sextus and Tunis roads in Oakland. For the convenience of comparison and contrast, new high-pressure sodium lamps are installed on the east side of Sextus Road, and LED street lamps are installed on the west side; LED street lamps are installed on all Tunis Road, and new high-pressure sodium lamps are installed on the adjacent Cairo Road. All lamps are installed 28.5 feet above the road surface, with a pole distance of 110, 120 or 160 feet.

The research results found that the average power used by each LED street light is 77.7 watts, which saves about 35% of the power of the average high-pressure sodium lamp (HPS) of 121 watts. Based on an operating time of 4,100 hours a year, it is estimated that 178 kilowatt-hours can be saved per year.

Before each stage of LED evaluation testing is carried out, there will be a pre-test operation. All tests are carried out after dusk. The distance between one lighting fixture and its second lighting fixture is 110 feet, the distance between the second and the third is 165 feet, and the distance between the third and the fourth street lamp is 120 feet. In reasonable circumstances, the lighting uniformity of the lamps should be the same, but in actual settings and evaluations, street lamps cannot be completely set within a yard when set at intersections. The distance from north to south is 12 feet, adjusted to 10 feet by the width of the street.

The measurement method of this evaluation project is slightly different from the method of measuring streetlights in the International Street Lighting Standard (IESNA). The International Street Lighting Standard recommends that the measurement position should be within a half-square range directly below the light source. The measurement range of this study is directly below the light source and the center point between the two light sources. The maximum and minimum values ​​of illumination are predicted within the test range, and the degree of difference in uniformity between high-pressure sodium lamps and LED lamps is recorded. The sensor is recommended to be installed at 6 feet above the ground. Considering past measurement experience and suggestions, the research team set the measurement position at 18 feet, which is the lowest height that can be reached when the tripod and sensor are combined.

The measurement process also includes temperature measurement, using an electronic thermometer to measure the high-pressure sodium lamp and LED lamp every 20 minutes; in addition, at night when measuring LED lamps , a HOBO instrument U12 data logger is used to obtain relative humidity and other temperature measurements every 30 seconds. The relevant measurement information about LED lamps and high-pressure sodium lamps includes photography from various angles, power , illumination, color temperature and ambient temperature, a total of four measurement items.

For the measurement of power consumption, a DENTElite data logger was used to measure a single high-pressure sodium lamp and an LED lamp. Since the test project lasted for a period of time, the measuring instrument had to be set at a height above the ground where it was difficult for people to directly touch it. The research project personnel relied on the Oakland street light maintenance team to assist in the installation and removal of the measuring equipment. During the measurement period, there were no special differences caused by power consumption.

Measurement results analysis

1. Differences between electricity demand and energy consumption

If the high-pressure sodium lamp is used for 11.97 hours a day, the average power consumption is 121W. Under the condition of 4100 hours of annual use, the total annual power consumption is 496kWh. If the LED lamp is used for 12.75 hours a day, the average power consumption is 78W. Under the condition of 4100 hours of annual use, the estimated annual power consumption is 319kWh. Comparing the two measurement results, it can be seen that the use of LED lamps can save 43.3W of power consumption, and it is estimated that 178kWh can be saved each year. The daily lamp use time is between sunrise and sunset. Because the test of LED lamps during the research measurement period is closer to winter, the average daily use time of LED lamps is slightly longer than that of high-pressure sodium lamps.

2. Illuminance measurement results

The measurement range of illumination is 395 feet by 36 feet, including 4 different positions, 110, 120 and 165 feet away. Due to the location of the street lamp, it is impossible to measure the illumination directly under the lamp, but the error affecting the overall study is not too large. The average illumination is calculated in foot candlelight, the maximum and minimum illumination of the lamp are measured, and the maximum/minimum uniformity is calculated based on the maximum and minimum illumination.

According to the measurement results, in general, the illumination of LED lamps is the same level as that of high-pressure sodium lamps or higher. In addition, since the illumination of LED lamps measured directly below the fixture is slightly dimmer than that of high-pressure sodium lamps, the uniformity of LED lamps is better. In darker light conditions, the illumination of LED street lamps can be maintained at the same illumination level or increased compared to high-pressure sodium lamps.

3. LED life and light decay

The life of a high-pressure sodium lamp is about 30,000 hours, and at 30,000 hours of use, the high-pressure sodium lamp is expected to provide 75-85% of the original luminous flux ; while the LED lamp can still provide 90% of the luminous flux at 30,000 hours of use when the ambient temperature is 25°C or lower. Since the surface of the bottom of the LED lamp is acrylic synthetic resin, the luminous flux will also be affected as the bottom turns yellow. According to local climatic conditions, after ten years of use, there may be a 2% impact due to the discoloration of the bottom of the lamp.

LED street lights have great potential for energy saving in lighting applications. From the evaluation results of this demonstration plan, we can see that the installation of LED street lights has a very positive impact on local residents in terms of visibility and nighttime safety. However, the initial cost of LED is currently high, and economic benefits and recycling cycles are still a major issue that relevant units and manufacturers attach great importance to. Even though the emerging technology of LED is gradually accepted by most manufacturers in the current trend of promoting environmental protection and energy saving, the government still needs to pay more attention to funds in the future, subsidize local demonstration plans and evaluations, and reduce the initial investment costs of manufacturers, so that LED can have a better prospect and growth space in the future street light market. Fortunately, China's LED street lights are currently experiencing unprecedented development opportunities driven by government projects, such as the " 10,000 lights in 10 cities " plan, as well as demonstrations at the Olympic Games/World Expo/Universiade. However, in this hot context, we have also noticed that manufacturers are rushing into the market, with uneven product quality, neglect of technology research and development, and excessive aggressiveness, which has led to frequent problems in actual applications, and has led to users' doubts about LED light sources. For example, according to the recent news from the editor of Optoelectronics News, Shenzhen is currently evaluating LED street lights on a road in the Science and Technology Park. Since it is an open test, any manufacturer can participate. However, within just one month, some companies have provided LED street lights that have "dead lights", which has partially affected users' confidence in LED lamps. Therefore, strengthening technology research and development and reserves, and improving product reliability and stability will be important factors affecting whether LED street lights can be truly popularized in the future.