There are different kinds of lights that car manufacturers use to illuminate the road in front of the vehicle for night driving. One among them is called Fog lights and they usually come in a yellow color although modern cars come with white light and even high intensity discharge lamps. These lights were designed in the first cars to provide close up and bright illumination of the road immediately in front of the vehicle, and is usually sharply cut off at the top so that the light does not go upwards but is reflected downward.
There are many explanations why these lamps are yellow in color, with the most common one being that yellow light has the greatest penetrative power through mist and fog. This is actually untrue; the water particles in the fog is actually too large to make a difference to the wavelength of the light used. What seems more probable is that car manufacturers thought that yellow being the caution light was a good color to use in foggy conditions considering that they would mostly be used in bad weather conditions. The assumption is that vehicles going in the opposite direction will see the yellow light and be more cautious.
According to a survey conducted in North America, it seems that nowadays most people who use these lamps do so in good weather conditions and do so more for the style quotient than anything else. Because of this car makers have ceased to use these lamps purely for utility, and have started designing very stylish lamps. Nowadays these lamps are not even found in the low end cars and come only in high end, or luxury cars.
The kind of lamps used also differ depending on the car, the manufacturer and the market segment which the vehicle is targeting. Starting from ordinary incandescent lamps, you can go through high discharge lamps, projector lamps and even LED lamps. Lighting technology has improved so fast that LEDs that could not be used even a few years back because they did not have the required output, are now being used, not only in premium vehicles but in lower end cars as well.
Most urban dwellers prefer to drive with their fog lamps on when driving within the city, because it does not cause as much discomfort to oncoming vehicle drivers as the main driving lights. Because of this the market for aftermarket lamps has grown tremendously and most car owners do not have to stick with the original ones. There will be a range of lamps to choose from, and even your humble family sedan can get a new set of lamps.
These lamps start off at around the $20 mark, and progressively increase depending on the type of lamp and the make and model of the vehicle it is for. Lamps for older model vehicles usually do not cost as much as the newer models. It goes without saying that if you are purchasing one for a luxury car, it will set you back a couple of hundred dollars, and may even cost more if you want to go in for a really stylish one, or one that incorporates the latest in illumination technology.
Whatever be the purpose for which fog lights are installed, they have ceased to be a utility feature and have now become a style statement, and considering that you get pretty decent looking ones which do not cost too much, a number of people have started going in for after market fitments. If you want to subtly change the way that your car looks, then this is probably what you will have to do too.