Why Are Most Street Lights In Cities Yellow

LED electronic displays are appearing more and more in people′s view, and LED lighting has also been tried on some major roads. So what conditions do LED street lamps need?

From the hustle and bustle of the day to the coming of night, when the lights are on, the city will gradually calm down after a busy day. Every city road, from the main thoroughfares to the tree-lined paths in residential areas, will be lit with streetlights to guide citizens home at night. At this time, have you found that most of our street lights are yellow? why not white or other colors?

First of all, light is made up of seven colors: red, orange, yellow, green, blue, violet. Different colors of light have different wavelengths, with red light having the longest and violet light the shortest. However, as the color of the illumination, not be the color of the longest light with wavelength is most appropriate, so gules light is most inappropriate, and red light is bigger to the stimulation of the eye.

The wavelength range of yellow light is 570-600 nanometers commonly, which is only a relatively sensitive band in the human eye, yellow light belongs to the warm color department again, far more than the color such as gules, orange is warm, won't stimulate the eye. So for street lamps, yellow light is the ideal color.

Before the appearance of LED, white light is mainly incandescent lamp, and street lamps on both sides of the road use yellow light as a high pressure sodium lamp. High-pressure sodium lamp is a kind of high-pressure sodium vapor arc discharge bulb, is the current high luminous efficiency of the gas source, the wavelength range of the light is in the yellow light band of visible light, so from our eyes, the color of the high-pressure sodium lamp is yellow. According to the data, the luminescence efficiency of high-pressure sodium lamp is several times that of incandescent lamp, the service life is twenty times that of incandescent lamp, the cost is lower, and the fog permeability is better. In addition, human eyes are sensitive to yellow light, and yellow light gives people a sense of warmth, which helps reduce the probability of nighttime traffic accidents.

Of course, high-pressure sodium lamps also have great disadvantages. The main disadvantage of high pressure sodium lamp is poor color rendering. Color rendering is an evaluation index of the light source. Generally speaking, it is the difference between the color displayed by the light source and the color of the object itself. The closer the display color is to the natural color of the object, the better the color rendering of the light source. Incandescent lamps have good color rendering and can be used in household lighting and other lighting scenes. But the color display of sodium lamp is poor, no matter what color of the object, see the past is yellow. Just right, road lighting is not high on the color of the light source, we can identify the size (shape) and speed of a car on the road as long as we can find a car coming from a distance, there is no need to distinguish the car is red or white.

It is also questioned that at present white LED technology is mature, why there are still a large number of street lamps using high pressure sodium lamp?

LED street lamps have the following advantages compared with ordinary high-pressure sodium street lamps:

1.Energy saving: at present, the luminous efficiency of white LED is about 80lm/W, which can save electricity by 50%~60% compared with the traditional high-pressure sodium lamp. With the rapid improvement of LED efficiency, semiconductor street lamps show great potential in energy saving.

2.Low maintenance cost: according to the current technical level and test results, high-power LED light source can be used normally for 10 years without replacement, and the traditional high-pressure sodium lamp will be replaced once in an average of one and a half years, the use of semiconductor light source can greatly reduce the maintenance cost.

3.Good color rendering: LED color rendering index is high (75~80), people's reaction speed, the road looks brighter, feel more comfortable, drivers also feel safer. The spectrum of high-pressure sodium lamp is narrow, the color rendering is poor (20~40), and the feeling is dim.

But at present, an LED street lamp needs about 100 1W white light on average. Therefore, the price of large-scale replacement of LED street lamps is relatively high, and it is difficult to promote and apply them in large areas in small and medium-sized cities according to different power and installation height. It is understood that LED street lamps are used to replace traditional street lamps all over the world. In accordance with the improvement of LED industry standards and specifications and the improvement of technical standards, the replacement and renewal of LED lights will also be accelerated in the road lights of small and medium-sized cities in the future.