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Why are most city street lights yellow?

August 14, 2023

People are increasingly seeing LED electronic displays, and several major highways have even experimented with LED illumination. So, what are the requirements for LED street lights?


The city will gradually get quieter as the day's activity fades into the approaching darkness as the lights are turned on. Streetlights will be erected on every municipal street, from major thoroughfares to tree-lined pathways in residential districts, to help residents locate their houses at night. Have you noticed that most of our street lights are currently yellow? Why not, as opposed to white or other colors?


To begin, there are seven makeup colors: red, orange, yellow, green, blue, and violet. The wavelength of red light is the longest, while that of violet light is the shortest. The wavelengths of different colors of light differ. Red light is more exciting to the eye than green light due to its longer wavelength, yet green light is undesirable due to the lighting's colour.


The wavelength range of yellow light is typically 570-600 nanometers, which is just a somewhat sensitive region in the human eye. Yellow light is also classified as a warm color, making it less exciting to the eye than warm colors such as red and orange. As a result, yellow light is the greatest color to utilize in street lighting.


Prior to the arrival of LEDs, white light was generally provided by incandescent lamps, while yellow light was created by high-pressure sodium lamps in street lamps on both sides of the road. A high-pressure sodium lamp is a type of sodium vapor arc discharge bulb. It currently has a high luminous efficiency and emits visible light with a wavelength that falls within the yellow light spectrum, giving it a yellow look to human eyes. According to data, high-pressure sodium lights have a higher luminescence efficiency than incandescent lamps, a twenty-fold longer service life, are less expensive, and have greater fog permeability. Yellow light is extremely sensitive to human vision, and because it makes people feel warm, it reduces the likelihood of nighttime traffic accidents.



Of course, there are several disadvantages to using high-pressure sodium lights. The primary disadvantage of high-pressure sodium lamps is poor color rendering. Color rendering is one of the light source evaluation criteria. In general, it refers to the difference in color between the item and the color represented by the light source. The more closely the display color approaches the actual color of the item, the better the color representation of the light source. Because incandescent bulbs render colors well, they can be used for home illumination and other lighting settings. However, the color display of the sodium light is poor; regardless of the color of the item, the past seems yellow. When used correctly, road illumination does not rely too heavily on the color of the light source; as long as we can see a car approaching from a distance, we can discern its size (shape) and speed without having to tell whether it is red or white.




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