Fog is a significant obstacle to vehicular traffic. Foggy weather is always accompanied by the light back-scattering effect, which means when drivers turn on their headlights, the foggy background intensity of their view increases, causing the view to become more blurred than before. And so instead of using headlights, we need something that has a better scattering effect in order to let the light beam as far as possible and be scattered into a larger area of light clusters. By achieving this, not only can drivers see what's ahead more clearly, but they also allow the driver of the oncoming car to be aware of the car that is using these lights while also not being blinded by the light beam.
That's why, when encountering fog, drivers always turn on the front fog lights so that a cluster of brilliant yellow lights opens up a path for them. Not only to illuminate the road ahead but also to mark their presence through the thick fog so that oncoming drivers and pedestrians can quickly evade and prevent accidents from happening.
Anti-fog lights can be divided into front fog lights and rear fog lights, the light color of the front fog lights is generally bright yellow, while the light color of the rear fog lights is red. Because of the high brightness and strong penetration of the anti-fog lights and the much lesser diffuse reflection when encountering foggy weather, the correct usage of anti-fog lights can effectively prevent accidents from happening. In foggy weather, we often turn on both the front fog light and the rear fog light at the same time.
The light coming out of the front fog lights is yellow, which is the best choice after careful research by scientists. You might wonder why we don't use the more eye-catching red light. Because red and yellow are the most penetrating colors, and because red light is commonly associated with "stop", yellow is the best option. Some may ask, "Within the light spectrum, don't green light, blue light, and purple light all have a stronger scattering effect than yellow light?" Why not choose them over the yellow light for the fog light? That's because green light has long been used as the "safe" and "passable" sign light; as for blue light and purple light, although they have a very short wavelength, they do have a stronger scattering than yellow light. However, they have an inherent weakness, which is a darker light color that is close to the light color of an evening, dawn, or cloudy day, and since the fog is most likely to occur at such a time, obviously they do not meet the requirements of the signal signs of the fog lights.
The scattering intensity of yellow light is five times stronger than that of red light, so it is obvious that the use of yellow light as the light color of automotive fog lights is much more efficient than with red lights. Furthermore, yellow is the middle-wavelength part of the visible light part of the electromagnetic wave, its wavelength is about 570–590nm. The yellow wavelength has a moderate wavelength and is the most luminous light color in all hues, so yellow light is the farthest spread and the most obvious color of light in the air. And lastly, yellow is the purest color, the yellow anti-fog automotive light can penetrate very thick fog and shoot to a very distant place.