For the determination of the early failure reliability of LED street lamp products, it is currently only necessary to strictly control the products entering. According to statistics released by the United States, about 30 of the accepted products with technical certification can reach the candidate. Of the candidate products, only one-third can actually adopt the actual trial assessment, which is about less than 10 products can be accepted for trial use. Only 2 of the final products tested.
Due to the unfamiliarity of the products entering the individual cities, the inspection and inspection of the procurement was not strict. The 2000 street lamps that were tested were found to be dismantled after several early failures in bad weather, and all the 25,000 products that were not installed were returned to the supplier. The case was announced on the Alliance Online, which attracted the attention of suppliers and cities, and promoted the future promotion of LED roads.
China does not have a public platform that reflects the quality of the project to prevent inferior products from entering the market and to avoid repeated errors.
Discussion of color temperature and color rendering
Regarding the color temperature problem of LED street lighting, it is still under discussion. From the experience of urban street use in the United States, starting from the bustling urban areas and street public safety, it tends to have a white color with a high color rendering index. It helps to identify various targets and facilitate crowd activities.
However, the color temperature above 5000K cannot be accepted. Traditional pure residential areas, suburban roads, prefer a lower color temperature, feel safer and warmer. It is recommended to use warm colors for the suburban trunk roads with high vehicle speed. The LED street lights installed in the initial trials are all relatively high in color temperature, and the possibility of color temperature down-regulation is currently being explored. The approximate range is between 3500-5000K.
Due to the one-sided emphasis on the light effect of the lamps, many of the LED street lamps installed in China have adopted high color temperature and low color rendering, which is difficult for the public to accept. Currently returning to low color temperature. Two cities, New York and Shanghai, call for a suitable color temperature of around 3,500K at night.
LED street light
One of the biggest uncertainties in the return of LED road lighting is the determination of the reliability of the light decay life of the luminaire. Light decay is a parameter that requires timeliness to verify. It is unrealistic to perform long-term tracking tests on the actual lamps used. However, due to such difficulties, giving up or relaxing the requirements for light decay of products will cause a large number of cheap and inferior lamps to be accepted by engineering and mixed into the construction in progress, resulting in the final failure of the project.
In the United States, the control method for the luminous efficacy of lamps is to accept only the street lamps that are selected with LED components certified by LM-80 and LM-79. It is actually proved that the products that meet the certified components are acceptable, and the light decay is acceptable for at least 7 years. Liaoning Avenue, which was rebuilt after the disaster in Mianyang, China, uses high-quality LED road lighting. The measured light decay in two years is 5.5, which is equivalent to the current US level and higher than the domestic average. The strict requirements of LED road lighting will prompt domestic LED components to pay more attention to product light decay indicators.
Requirements for LED road lighting uniformity
Public lighting in the United States generally emphasizes uniformity in square lighting. Ordinary road lighting pays more attention to the lighting performance of lighting, emphasizes the key lighting, and does not pursue the high uniformity of road lighting. The distance ratio of urban street lights is generally larger than that of China, generally more than 3; in residential areas of non-commercial areas, the road illumination is low, and the distance is higher than the height of 3 is not uncommon. However, in the intersections or places where residents enter and exit, enhanced lighting is provided to provide dual effects of lighting and warning.
The latest special research shows that the illuminating road lighting is more in line with human natural habits of night lighting, and can improve visual alertness. The uniform lighting environment is easy to produce visual fatigue, reduce the ability to detect targets, and is not conducive to driving safety. Moreover, artificially constructing excessive uniform road lighting is not only technically difficult, but also expensive, lighting efficiency is low, and glare is increased. It is definitely a choice that is not worth the candle.
China's LED lighting project status, because the road illumination uniformity index is easy to detect, project acceptance is convenient, and the perception is obvious, the media publicity effect is good, so the uniformity is often overemphasized in China's LED lighting engineering design. Most demonstration projects exceed the required standards in terms of uniformity and are considered to be the most prominent indicator. To this end, the use of ultra-low aspect ratios has greatly increased construction and operating costs. However, this new and slick and bright project is not enough to become a model for the promotion and application of LED road lighting, and eventually become a negative textbook.
New understanding of LED glare
The most criticized indicator of LED road lighting applications is the string light produced by the new luminaire. Many LED illumination designs with threshold increments of TI are still perceived to have significant discomfort or even near disability glare.
This is due to the fact that unlike traditional luminaires, which use large-area reflectors, LED luminaires use direct projection. The illuminating light source has a small area and tens of thousands of cd surface brightness per square meter, which is thousands of times higher than that of ordinary lamps. The high resolution of the naked eye allows the LED light source to produce intense stimulation directly on the local retinal cells rather than just the light curtain. Threshold incremental standard TI based on light curtain theory and spatially very low resolution measurement methods are completely indistinguishable from this visual difference.
For such a high-intensity light source, it is currently recognized that it can only be solved by the cut-off method, and cannot be judged by the conventional threshold increment TI index. But in theory any method of controlling the string light must be at the expense of efficiency. This is a challenge to the future of LED road lighting technology.
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