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How do LED street lights remain penetrating in foggy days?
Mar 15, 2019

1. The color temperature of some common light sources
LED light sources can be broadly divided into warm white, neutral white and cool white. The traditional street light source - sodium lamp discharge radiation is concentrated on two double D lines of 589.0 nm and 589.6 nm, so the color temperature is generally about 2300K warm white light, it is obvious that it is yellow light under human vision. LEDs can be used to create light sources of different color temperatures through the packaging process, giving many different options for road lighting.
2. LED street light color temperature selection
At present, the LED packaging process can obtain LED white light sources of different color temperatures by applying phosphors of different excitation wavelengths and adjusting the amount or proportion of phosphors.
The color temperature of light emitted by different light sources is different. The characteristic of low color temperature light source is that red radiation is relatively more in the energy distribution, which is usually called “warm light”; after the color temperature is increased, the energy distribution is blue radiation. The increase in proportion is often referred to as "cold light."
For white LEDs, the low color temperature source has a relatively high proportion of yellow light, while the high color temperature source has a relatively large proportion of blue light. From the perspective of human vision, the low color temperature gives a warm, stable feeling, while the high color temperature gives a feeling of calmness and refreshment.
3, the relationship between color temperature and light efficiency
It is worth noting that in the early batch selection of LED street light color temperature, almost all manufacturers have chosen 6000K, or even more than 6000K, which runs counter to the high-pressure sodium lamp. Why?
Because of the technical conditions of the early phosphors, the LED of the cool white light source is more efficient. Compared with color temperature, people pay more attention to the physical properties of light effect. The most important means to improve the light efficiency is to improve the excitation efficiency of the phosphor. The excitation efficiency of YAG yellow powder is much higher than that of orange powder.
Obviously, higher color temperature can achieve higher light efficiency, and the light source efficiency of 5500-6500K color temperature is even 48.7% higher than that of warm white light source less than 3500K. The reason why LEDs are energy-saving is because LEDs have higher light efficiency than other light sources. It is meaningless to talk about energy saving simply. Therefore, in order to pursue high energy-saving rate, most LED street lamp manufacturers have chosen to produce products with a color temperature of about 6000K.
High luminous efficiency not only leads to higher energy saving rate, but also reduces the cost of the lamps and makes the products more competitive.
With the development of various LED technologies, the efficiency of LED chips has been continuously improved, and the packaging process has been continuously improved. The white LED light effect in the application has already broken through the barrier of 160lm/W, and there is room for improvement in the future. The technology of phosphors has also made some breakthroughs. At present, the difference in white light LED light efficiency between different color temperature ranges is not as great as before. The light effect of the warm white LED light source of 3000-3500K color temperature is different from the cold white LED light source of 6000-6500K color temperature. Less than 6%.
4, Rayleigh scattering
Why different colors of light have different penetration in the fog. Here is the introduction of a physics phenomenon called Rayleigh scattering. Rayleigh scattering is an optical phenomenon. When the particle radius is much smaller than the wavelength of the incident light (less than one tenth of the wavelength), the medium is generated due to the non-uniform refractive index. The intensity of the Rayleigh scattering and the wavelength of the incident light λ The fourth power is inversely proportional, and this phenomenon is called Rayleigh scattering.
For a simple example, we can use Rayleigh scattering to explain why the sky is blue. Since the intensity of Rayleigh scattering is inversely proportional to the fourth power of the wavelength, the shorter wavelength blue-violet light in the solar spectrum is more pronounced than the longer wavelength red light scattering, while the short wave has the largest blue light energy, so in the rainy days When the weather is clear or the weather is high (the air is coarser than the coarse particles, the molecular scattering is dominant), in the atmospheric molecules, the light has strong Rayleigh scattering, and the blue light is scattered to the diffuse sky, so the sky is blue.
Simply put, the shorter the wavelength, the easier it is to dissipate heat, and the longer the wavelength, the easier it is to penetrate. The main factor in the formation of haze is that PM2.5 is composed of many small particles, which cause Rayleigh scattering of light.
The proportion of blue light in cold white light is large, and the proportion of yellow light in warm white light is large. Theoretically, the lower the color temperature, the greater the penetration of light. Therefore, under the smoggy conditions, the high color temperature LED street light has poor penetration.
5, human senses
From the perspective of penetrability, LED street lights should choose red light with low color temperature. However, the lighting of street lamps gives people a sense of the sense of being an important factor that cannot be ignored. Human senses mainly include both psychology and physiology.
From a psychological point of view, the human eye has different sensory perceptions for different color temperatures under different illumination conditions. In an indoor environment, under certain illumination conditions, too high a color temperature will give people a feeling of depression, which seems to be deserted and hazy; and a low color temperature will give people a feeling of sultry, appearing dim and depressed. In the outdoor environment, the human eye needs to make some corrections to the color temperature, and the comfort zone will extend to a high color temperature region.
In recent years, LED technology is still developing at a high speed, and the light efficiency of the chip is continuously improved, and the energy saving rate is also guaranteed. The contradiction between light efficiency and color temperature is no longer the main contradiction in the application process. Whether color temperature and environmental conditions are coordinated is the focus of attention.
In summary, the comprehensive technical conditions, climatic conditions, current environmental conditions and the senses of the human eye, we propose that the color temperature of LED street lamps should be selected within the range of 2800 ~ 4200K. Such color temperature will not have a great impact on the light effect, but also ensure the penetration of fog and cockroaches, and adapt to the visual sense of our people.cree-chips-oem-50-120w-bst-1012n-l-sedan-led05035829270

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