Why are the lights of the street lights yellow?

Regardless of the LED, there are only a few types of lights, each of which corresponds to a specific range of colors. If you want to emit light of any color, you can only add a colored lampshade in front of the incandescent lamp. The traffic lights have been so dry (until the LED universal).

Most of the street lights are yellow, because these street lights use sodium lamps (now generally high-pressure sodium lamps), relying on metal sodium vapor to emit light. Specific principles, if you have studied high school chemistry, you should know the flame color reaction. This is basically the same thing. High school physics seems to talk about elemental spectroscopy. If you don’t know, you can Baidu. It’s too far.

Then why choose sodium lamp.

The reason is easy to think of, among all kinds of traditional electric light sources, the sodium lamp has the highest luminous efficiency, or in other words, it costs the least electricity to emit the same light. At the same time, the bulb has the longest life span, reaching more than 20,000 hours.

For street lights, the most important thing is to ensure that you see objects and ensure traffic safety; distinguishing colors is not so important. Whether the car on the opposite side is black or red makes no difference to pedestrians hiding behind them.

Therefore, choosing sodium lamps with higher luminous efficiency and longer lifespan consumes the same amount of electricity, allowing the lights to cover more roads and reducing maintenance costs.

But this does not mean that color rendering is not important. Low-pressure sodium lamps are basically eliminated from the field of street lamps, the main reason is the poor color rendering.

With the maturity of LED light sources, the light efficiency has been close to or even surpassed that of high-pressure sodium lamps. With the further development of technology in the future, the field of street lamps will gradually be occupied by LED light sources with excellent color rendering.