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(2009-12-22)LED street lamp application in rainy and mist weather shows advantages to traditional HPS by theoretical research
Most people think that the light-admitting quality of LED street lights is poor than traditional sodium lights when in the rainy and mist weather. People getting the misunderstanding through the Internet or just by the sense of the naked eyes on the street illumination, and make the conclusion that the penetrability of LED Street light is poor. They never do the scientific test and analysis.
As we all know, people can identify the brightness with the visual spectrum from 380nm to 780nm, thus, the lamps should applied light emitting within this range, or people will not feeling of the light. Here below is the visual spectrum of HPS and LED lamps respectively, through the scientific and reasonable analysis, we make conclusions that:
The spectrum of LED lamps is broader than HPS’s, the blue light of LED takes 6% of total lumens while HPS almost gets nothing for the peak of both is at 580nm.
The particles in the air and raindrop make the light scatter and the penetrability lower, so it is influences on the lux of lighting fixture when in mist and rainy days. The scattering law of visual spectrum of visual spectrum stands for the semi-diameter of particle, and it works with rayleigh’s law when r<0.037μm,and Mi-Debye jauncey scattering law when r>0.037μm. There are relations of wave length with the effectiveness of Rayleigh’s law of scattering when MI-Debye Jauncey are not. In other word ,the penetrability of LED street lights is the same of HPS because of there has no relation with the color of the light.
People always think the penetrability of HPS is stronger than LED lights by recognition of their own experience, compared to the dark yellow HPS light, LED light is white in the mist and people may see the sodium light much easier than LED light.
Normally, it is much easier to see other colors on the white background while people pay more attention to the illumination of many areas but not for street lamination. Actually, LED street lightis on the illumination of road surface directly.
The CRI is important in mist weather of Street illumination especially in thick fog situation; the CRI of HPS is around 17, much lower than LED light for 60 to 80. Mainly because of HPS is lack of blue light spectrum, which makes things look like black one under the light from HPS. For instance, when people in blue cloth walking on the street and there is blue obstacle in the road, the blue things will be hidden from the background of HPS light in the thick mist, and easy to cause car accident. And people may see the blue obstacle under the illumination of LED.
There is a difference between multi-LEDs and integration LEDs for that Multi-LEDs has a wider area of lighting than integrated LEDs but lower brightness on the surface. Therefore, for mist days, the packaged integration LED is a little bit better for the direct illumination which makes people see the road clearly in the thick mist weathers.
We may draw a conclusion of above, people always take and misunderstanding for that penetrability of HPS is better than LED street lamps in the mist weather, but LED street lights are much better for the street lighting when considered to the CRI with the visual identification for the objects in mist weather, and then considering the lux on illumination, we may take integrated LEDs in street lighting of mist weather.