There is a misunderstanding on the recognition of penetrability about the LED street lamp lumination in the rainy and mist weather. Most of us believe that the penetrability of LED street lamp is lower than the conventional sodium lamp,which is a misunderstanding. Most of the people get the result by reading the material from the Web or just by the sense of the naked eyes on the road illumination. However, they never do the scientific test and analysis. They just simply conclude that the penetrability of LED street lamp is not so good. Hereby, we would like to make a scientific analysis on this issue.
As we all known that,the visual spectrum is from 380nm to 780nm, people can see and identify the light within this range. In other words, only the light emitting within this range from the lighting fixture has the value of application, humans can't identify the light out of this range. We analyzed the penetrability of LED street lamp base on the visual spectrum, here below is the visual spectrum of HPS and LED lamps respectively.
From the spectrum above, we can see that the spectrum of LED is broader than the HPS's, the peak of both is at 580nm, the blue light of LED takes 6% of the total lumens, while HPS nearly gets nothing. The red light of LED is much broader than the HPS's.
There are several influences in mist and rainy days when the road lamp works. The particles in the air and raindrop make the light scatter,which enable the penetrability lower and makes the lux of lighting fixture decrease quickly and directly. The theory of light scattering on the particle in the air is based on the Rayleigh's law of scattering and Mi-Debye Jauncey scattering law. The scattering law of visual spectrum works within ranges as below,r stands for the semi-diameter of particle;it works with Rayleigh's law of scattering when r<0.037μm,it works with Mi-Debye Jauncey scattering law when r>0.037μm. The effectiveness of Rayleigh's law of scattering on the light has the relations with the wave length,Mi-Debye Jauncey scattering law has not.In other word,the penetrability of street lamp has no relation with the color of the light, in fact, the penetrability of LED street lamp is the same as HPS's!
From the recognition of conventional experience,people may believe that the penetrability of HPS is stronger,this is just a sense from organic.The color of HPS light is dark yellow, LED light is white,and the mist is white, too. Apparently,people can see the sodium light much easier than LED light on the background of white mist!
It's much easier to find other colors on the white background,and harder to find white color on the background of white color. This effectiveness is applied in many areas on the illumination,however,it's nothing for street lumination,because all of us pay more attention on the illumination of road surface direction!
The CRI can't be ignored on the street illumination in mist weather,especially,in thick fog situation.The CRI of HPS is around 17, the CRI of regular LED is from 60 to 80. The CRI of HPS is much lower because lack of blue light spectrum. The blue object looks like black one under the light from HPS,it means that no light was reflected from the blue object under the illumination of HPS. When people in blue cloth walking on the street or there is blue obstacle in the middle of the road, the blue object just can't reflect light under the illumination of HPS! Therefore, the blue object will be submerged from the background of the light in the thick mist,people can't see the blue object, it will cause car accident. Nothing happens if it's under the illumination of LED!
In addition, there is a difference between multi-LEDs and integration LEDs.Multi-LEDs has greater lighting areas,the brightness on the surface is lower,the packaged integration LED has smaller lighting area and higher brightness on the surface.Therefore,the illumination direction of packaged integration LED is a little bit better,it makes people see the direction of road clearly in the thick mist weather,it works better in the mist days.
All in all,it's indeed a misunderstanding that people conventionally believes the penetrability of HPS is better than LED street lamp's road illumination in the mist weather. Theoretically,our above analysis shows that the penetrability of HPS is not as good as LED's. In contrast,from the view of CRI,the LED street lamp has better visual identification for the object in the mist weather.Besides,considering the lux on illumination surface, integrated package LEDs has better effectiveness in the mist weather.