Street Lighting

Why Is A Yellow Color More Common In City Street Lighting Than White?

When I go home in the evening, my careful friends will find that the street lights on many roads are lit up, and most of these street lights are yellow. Why should the street lights be yellow instead of other colors? In fact, this is related to the color, wavelength and illumination effect of the light. The following small series will take you to understand why the street light is yellow.

Why is the light of the street light yellow?

Different wavelengths give the human eye different color perceptions, from red, orange, yellow, green, blue, enamel (blue-violet), and purple. The sensitivity of the eye varies strongly with wavelength. For example, under good lighting conditions, the eye is 20 times more sensitive to light at 550 nm (yellow) than red or blue.

This is also an important reason why fog lights and road lights in most cars use yellow light. Color temperature is a measure of color temperature and is not a measure of the brightness of a lamp.

The color temperature of the halogen lamp can be from 2300K to 7000K; the color temperature of the HID lamp is from 4200K to over 8000K; the higher the color temperature of the lamp, the worse the penetration of fog and rain (the less bright). The night came, the city became brightly lit, and the road was brightened by a street lamp . At this time, you will find that almost the entire city is covered in yellow light. 

Let us first understand the color of light and light. Light is a kind of electromagnetic wave, and the whole electromagnetic spectrum includes radio waves, infrared rays, visible rays, ultraviolet rays, and X-rays. Among them, visible light is the part of the electromagnetic spectrum that the human eye can perceive.

In general, visible light consists of seven different colors of light, namely red, orange, yellow, green, cyan, blue, and violet. The color of the light is different, and the wavelength is different: the wavelength of red light is the longest, and the wavelength of violet light is the shortest. The wavelength range of yellow light is 570-600 nanometers, which is in the sensitive band of the human eye. At the same time, yellow is a warm color system, so it is one of the ideal choices for the color of street lights.

The following are the performances of different color temperatures:

Light color temperature effect

3000K yellow light, strong penetrating power

4200K white with yellow, the original car with the xenon lamp

5000K light all white, the highest color temperature in Europe

6000K light all white, slightly blue

Daytime under 6500K sunlight

7000-8000K white with obvious blue

Blue light above 8000K, poor penetration

Recommended street light color

The color temperature of about 6000K is just the color temperature of the whitest slightly starting to turn blue, the human eye is easy to accept, not easy to fatigue, improve safety, and the halogen lamp is poor. Let us look at the choice of urban street light source.

There are many types of light sources. The researchers compared the performance and price of different light sources, and finally chose high-pressure sodium lamps as the light source for street lamps. The high-pressure sodium lamp is a kind of bulb with high-pressure sodium vapor for arc discharge, and is a gas source with relatively high luminous efficiency. The wavelength range of the emitted light is in the yellow band of visible light, so it is seen from our eyes that the light from the high-pressure sodium lamp is yellow.

So, what are the benefits of using high-pressure sodium lamps? In addition to high luminous efficiency, it also has the advantages of low power consumption, long life, strong fogging ability and no trapping. It not only makes people and cars look at the road well at night, but also the light is very soft, so many High-pressure sodium lamps are used as much as possible in traffic lanes and artificial lighting to reduce the incidence of traffic accidents. There are two kinds of yellow street lights, one is a high-pressure sodium lamp, and the other is a warm-light LED street lamp .

High-pressure sodium lamps have the characteristics of high luminous efficiency, strong penetrating power and low corrosion resistance. Therefore, high-pressure sodium lamps will be used in seaside cities, ports, and northern cities, and even in foggy weather, there will be good lighting effects. Warm light led color temperature is 2500K – 4500K, the lower the color temperature, the more yellow the color.

Now that we know why street lights are orange, let’s look at whether or not they should still be so.  The answer isn’t as straightforward as it might seem.  Although newer technology seems to surpass HPS in nearly all respects, there are still considerations to be made.

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