Air quality has deteriorated sharply in recent years, with many large and medium-sized cities also facing smog. In some cities, the average number of smoggy days per year exceeds 100. Cities with severe smog are mostly economically developed and often take the lead in the promotion of LED street lamps. Therefore, it is of great significance to study and discuss the selection of LED street lamps in haze weather.

LED light sources are divided into warm white light, neutral white light and cold white light. The discharge radiation of traditional street lamp and sodium lamp is concentrated on two double D lines of 589.0nm and 589.6nm, so the color temperature is generally 2300K warm white light, and the human vision is obviously yellow. LED street lights can be packaged to create light sources of different color temperatures, thus providing many different options for road lighting.

At present, LED packaging technology can adjust the amount or proportion of phosphors by applying different excitation wavelengths of phosphors, so as to obtain LED white light sources with different color temperatures. Light from different sources has different color temperatures. Low color temperature light sources are characterized by relatively more red radiation in the energy distribution, which is often called "warm light". When the color temperature rises, the proportion of blue radiation in the energy distribution increases, usually called "cold light". For white LED street lamps, the proportion of yellow light in low temperature light source is relatively high, while the proportion of yellow light in high color temperature light source is relatively high. From the perspective of human vision, low color temperatures give people a feeling of warmth and stability, while high color temperatures give people a feeling of coolness.

It is worth noting that in the first batch of LED street lamp color temperature selection, almost all manufacturers choose 6000K, or even more than 6000K, which runs counter to the high-pressure sodium lamp. Why is that? Because in the early phosphor technology conditions, cold white light LED is more efficient. People pay more attention to the physical properties of light effect than color temperature. The most important way to improve the optical efficiency is to improve the excitation efficiency of phosphor. The excitation efficiency of yellow powder is much higher than that of orange powder. Obviously, higher light efficiencies with higher color temperatures can be obtained. The light efficiency of 500 ~ 6500 K color temperature is 48.7% higher than that of the warm white light below 3500K.