How do LED street lights maintain penetration?

- Aug 08, 2019-

1. Color temperature of some common light sources

LED light sources can be broadly divided into warm white, neutral white and cold white. The discharge radiation of traditional street lamp light source -- sodium lamp concentrates on the two double D spectrum lines of 589.0 nm and 589.6 nm. Therefore, the color temperature is generally about 2300K of warm white light, which is obviously perceived as yellow light under human vision. Leds can be packaged to create light sources with different color temperatures, giving road lighting many different options.

2. Color temperature selection of LED street lamps

The current LED packaging technology can obtain LED white light source with different color temperature by applying phosphors with different excitation wavelengths and adjusting the amount or proportion of phosphors.

The color temperature of light emitted by different light sources is different. The characteristics of light sources with low color temperature are that, in the energy distribution, there is more red radiation, which is usually called "warm light". When the color temperature increases, the proportion of blue radiation in the energy distribution increases, which is often referred to as "cold light".

For white leds, the ratio of low color temperature sources to yellow light is relatively high, while the ratio of high color temperature sources to blue light is relatively high. From the perspective of human vision, low color temperature gives people a warm and stable feeling, while high color temperature gives people a cold and refreshing feeling.

3. The relationship between color temperature and light efficiency

Under the technical conditions of early phosphors, LED with cold white light source is more efficient. Compared with color temperature, people pay more attention to the physical properties of light efficiency. The most important way to improve the light efficiency is to improve the excitation efficiency of phosphor powder. The excitation efficiency of YAG yellow powder is much higher than that of orange powder.

Obviously, higher color temperature can get higher light efficiency. Light efficiency of light source with color temperature of 5,500-6500k is even 48.7% higher than that of warm white light source with color temperature of less than 3,500k. The reason why LED saves energy is that LED has higher light efficiency than other light sources. It is meaningless to talk about energy saving regardless of light efficiency. Therefore, it is understandable that most LED street lamp manufacturers choose to produce products with color temperature of about 6000K in order to pursue high energy saving rate.

High light efficiency not only brings higher energy saving rate, but also reduces the cost of lamps, making products more competitive.

With the development of various LED technologies, the efficiency of LED chips has been continuously improved, and the packaging process has also been improved. Currently, the applied white LED light efficiency has already broken the 160lm/W barrier, and there is still room for improvement in the future. Meanwhile, phosphor technology has also achieved some breakthroughs. At present, the difference of light efficiency of white LED in different color temperature range is not as big as before. The light efficiency of warm white LED light source with color temperature of 3,000-3,500k is less than 6% different from that of cold white LED light source with color temperature of 6,000-6500k.

Considering the technical conditions, climatic conditions, current environmental conditions and human eyes' senses, we propose that the color temperature of LED street lamp should be within the range of 2800 ~ 4200K. Such color temperature will not have a great impact on light efficiency, but also ensure the penetration of fog and haze, and adapt to the visual sense of the Chinese people.