LED lights don’t say so long

Longevity is just a legend

On a certain group purchase platform, various supplies groups in the beginning of the school season flocked to open the group, of which only LED eye protection table lamps have opened two or three groups. “No stroboscopic, eye protection” is the selling point that attracts the most attention of mothers, and its long service life makes many mothers feel incredible. A mother asked weakly, "Where can I buy a replacement bulb?" The head of the group posted the manufacturer's standard answer: "The normal life of LED small lamp beads (SMD) is 20,000-4,000 hours, conservatively calculated. It takes ten years and eight years, no need to change the light bulb."

However, Beijing (real estate) consumer Ms. Zhou recently reported to the newspaper that when she bought LED desk lamps three years ago, the promoters said that they would like to use the LED lights to change the bulbs, because it can last up to 100,000 hours. I didn't expect that the small light bulb from the end of last year would start to flash, and some of them were completely unlit. She asked a number of shops and was told that they could not be repaired. The brackets of the lights were still good. It was a pity to throw them. "We have always kept environmental protection, energy saving and longevity in the mouth, but in reality, there is still a big problem in longevity." Yu Anqi, a professor-level senior engineer and senior auditor of the National Lighting Quality Supervision and Inspection Center, said that in landscape lighting and backlighting. On the LED, LED can basically achieve longevity, but in the field of general lighting, LED can not achieve high efficiency and longevity.

Liu Shengping, chairman of the China Lighting Association, told the reporter: "The LED lamp is more energy-efficient and efficient, but its actual service life has yet to be tested." The reporter reviewed the instructions for using various LED eye-protection lamps and found these products. The service life is mostly 50,000-100,000 hours. If you use 4 hours of use per day, then these products should have a lifespan of decades. However, Liu Shengping pointed out that the service life of corporate propaganda is a theoretical value, and the product often does not reach such a long use time in actual use.

In this regard, Liu Shengping explained that if it is a bulb-type LED lighting product, the bulb may be replaced if it is broken. But now most of the products are "starry" type like the lamp of Ms. Zhou's house. The light source part is a whole module, and the modules of each product are not standardized even if they are produced by the same company. It is possible to change a module like a light bulb, so once it fails, it can only be eliminated. This is indeed a waste of social resources.

Life assessment problem to be solved

Zou Nianyu, director of the Institute of Optics, Dalian University of Technology, said that the above problems are also the difficulty in the reliability evaluation of LED lighting.

According to reports, the life performance measurement and evaluation of traditional light sources have been standardized. Due to their short life and interchangeability, whether it is incandescent or energy-saving lamps, the replacement of the bulb will not affect the continued use of the lamp, so generally The life of traditional light source luminaires is not evaluated. However, LED lighting products have a long life, and it is obviously inappropriate to evaluate the life of the LEDs through long-term experiments. At the same time, there are many forms of LED lamps, and most of the LED lamp sources are not interchangeable, so the life of different LED lamps can only be determined by the relevant life evaluation.

At present, the use of accelerated experiments to predict the life of LED lighting products is a very important means, the main mechanism is to let the stress level of the device work higher than the actual stress experienced in normal use, effectively stimulate product exposure failure, thereby shortening The normal time of device failure caused by a specific failure mechanism. However, for LED luminaires, due to its complex structure, there are many factors that affect its life. For example, the life of the LED light source itself, the LED driver and the environment all affect the life of the luminaire. And because the technology is still improving, the life of LED lamps should be evaluated after the technology is relatively perfect. However, before the LED technology is relatively perfect, it is necessary to establish a scientific and applicable LED lamp life evaluation method and evaluation model.

In addition, the definition of the life of LED lamps is still open to question. Because LED luminaires are different from the characteristics of a single illuminant of a conventional light source, it is composed of a plurality of illuminants and emits light. There is a color difference between the illuminants, and changes in color temperature and color rendering should also be in the definition of lamp life. Under consideration. For example, after using a LED luminaire for a period of time, its lumen maintenance rate is still as high as 50% or its performance is still higher than 70% of the initial performance, but its color rendering may not meet the requirements of use, then according to actual use, The end of life of the luminaire should be assessed, but according to the definition given in the current National Semiconductor Lighting Engineering R&D and Industry Alliance Recommended Technical Specifications, the life of the luminaire is still not final and can be used. Zou Nianyu believes that when defining the life of an LED lamp, it is necessary not only to pay attention to the maintenance rate of the light, but also to consider the relevant indicators such as color temperature and color rendering.

Zou Nianyu said that many researchers at home and abroad are working on the development of new LED lamp life evaluation methods, but so far no convincing model of the whole lamp life evaluation has been established.

According to the DOE report, there is currently no very viable way to assess the life expectancy of luminaires in the industry. Despite improvements in current lumen maintenance testing and planning standards, drive life and system color maintenance are still difficult to quantify. The DOE report is intended to define existing standards and planning standards, and the analysis identifies existing deficiencies that define the performance of LED luminaires. The report pointed out that the main problem lies in the fact that the existing method uses lumen loss as the only elimination mechanism for LED luminaires, and there is no standardized evaluation method to solve component problems other than light sources.