1 Introduction
In recent years, LED light source has been recognized and valued by its high efficiency, longevity and environmental protection. At the same time, with the rapid development of LED technology in the past 10 years, the related secondary optical design technology of LED has become more and more mature, replacing the existing semiconductor light source. Urban road lighting sources have become a major trend in the field of semiconductor lighting, and have received increasing attention. However, in order to promote LED street lamps in a large amount, it is necessary to have a unified technical standard and measurement standard for LED street lamp products, and stipulate some mandatory performance indicators to ensure the performance and quality of the products. From the current status quo of LED street lamp product technology development, the most important ones are the lamp life, the whole lighting effect and the light decay curve.
LED street light as a system, many factors affecting the above performance, such as the characteristics of the power drive, the weather resistance of the optical components, the waterproof and dustproof performance of the whole lamp structure, etc. will seriously affect the light efficiency and life of the system, that is, the LED for light The optical characteristics of the chip or module do not fully describe the performance of the luminaire. Therefore, the aging test of the whole lamp must be performed to obtain data that meets the actual performance of the system.
As the LED street lamp for outdoor lighting products, the reliability must be carried out on-site long-range test. The time span often takes thousands of hours. The accuracy of the long-range measurement on site is affected by environmental and test methods, and it will be compared with indoor experiments. The test results of the room environment produce large differences.
Figure (1) compares the light fading results of different LED street lights provided by a number of companies organized by the inspection department in the laboratory environment and in outdoor venues.
Figure (1) shows the 2000 hours of light decay test data for 22 LED street light products. It can be seen from the figure:
A. The light decay value of the LED street lamp tested in the outdoor field is greater than the light decay value tested in the laboratory environment;
B. If it is based on laboratory tests, most of the light decay is below 5%, and if it is based on outdoor tests, the light decay of these street lamps is obviously too large, and it is not suitable for mass production;
C. The test difference corresponding to different street lamp products is also different, ranging from 5% to 15%.
This has caused difficulties for the end user to choose LED street light products, that is, what method should be used to detect, which group of test data should I believe?
At present, in the standards and norms related to LED street lamps at all levels, strict requirements are imposed on the light decay of LED street lamps. Basically, after 3,000 hours of continuous lighting, the road lighting is not higher than 2%; High light fading tests require that all types of critical factors that cause measurement errors must be analyzed and appropriately compensated.
2. Main factors affecting the measurement accuracy of LED road lighting efficiency
For the life expectancy measurement method of LED street lamps, the relevant national standard gives the method for measuring the life expectancy of LED street lamps. The method stipulates that the LED street lamps are measured under the conditions specified by certain technical specifications, and the outer casing of the LED street lamps is monitored at the specified temperature measurement points. Temperature rise. The illuminance at the lower point of the LED street light at a certain distance is recorded every 100~300 hours until it reaches 6000 hours. If the life of the LED street lamp has not been reached until 6000 hours, the life of the LED street lamp, that is, the life expectancy, can be pushed out by the law that the illumination below the lamp is lowered. In the life expectancy measurement and the extrapolation calculation, the LED street lamp has an initial value of the light-emitting characteristic at 1000 hours, and the time when the outward-out LED road lamp flux drops to 70% of the initial value is the expected life.
It can be seen that the LED street lamp should be tested for light decay and life, and the time span is more than 3 months. Because the impact of the test site often needs to be tested at the street lamp installation site, as shown in Figure (2).
