subject: Fog Lights Are Essential During Misty Conditions [print this page] In cold, foggy, winter days, when motorists have to move about in their vehicles, they must have fog lights. These are mounted in the front of a car, very close to the normal headlights and used in misty conditions. Unlike other headlights, these are yellow in color. A good fog light can produce a wide bar shaped beam of light that has a sharp horizontal cutoff that helps in showing the darkness above and bright yellow below the beam. This makes it easier for the driver to see the road as well as any other vehicle in front and its proximity. As there is minimal upward distortion, the area above the beam can also be seen clearly.
Why are fog lights yellow in color? There is no specific reason for that. However, to make a layman understand, scattering of light is much higher in lights short wave length. To have the greatest penetration of light through fog, the color of light in the spectrum that has the longest wave length should be used. Red cannot be used as it is used for tail-lights and stop lights. So the next best thing was the color yellow. However, this reason is flawed. Fogs moisture droplets are smaller than droplets from clouds but at the same time are huge compared to the wavelength of visible light. The scattering of light in foggy conditions is quite independent of wavelength.
The earlier fog lights were incandescent lamps that had a filter placed over white headlights. This means that the penetrative power of these yellow fog lights becomes less. In fact, it would be better if white light be used instead of yellow light as fog lights. But, these yellow fog lights indicate to passing drivers that visibility is poor and extreme caution is required to prevent collision.
In Europe and other countries that stick to ECE Regulations, all vehicles must have two bright red 'rear fog lights, also called fog tail lamps. These look like high intensity lamps positioned at the rear end of the vehicle so that drivers following the vehicle can easily see the vehicle in the front, even in poor visibility. This light usually has 150 to 300 candela, which is similar to the stop lamp.
Headlights are those that assist the driver to see well in darkness. There is no specific color for headlights, but is usually pale yellow. This color does not affect the eyes of drivers who are approaching and it gives a good beam of light. There are many aspects to a good headlight, which are:
1. It should give a good beam of light that penetrates the darkness up to at least 100 meters.
2. The beam of light should be in an arc.
3. The driver should have the facility to dip the headlights or keep them full depending on his need. If the road is bad, the headlights should be dipped.
