Automobile headlights are designed and manufactured to be parabolic reflectors, making them perfect for use as fire starters. The old style headlights, with the large glass bulbs that had the reflectors built into them were hard to use for this, but the newer style, where the reflector is part of the light housing and the bulb sticks into it from the back are extremely easy to use.
To use a headlight, you’ll need to take the bulb out and remove the headlight housing from the car. If your lens is at all cloudy, you’ll want to separate the reflector from the lens; however, if the lens is clear, you might want to try using it intact, before taking it apart. These units are expensive, so there’s no reason to destroy your headlight if you don’t have to.
It is easy to determine the focal length of the reflector by looking at the bulb that goes in it. If you can find the filament in the bulb and figure out where it sits when it is installed in the headlight housing, you’ll have found the focal point.
Put the tinder that you are going to use to start your fire into the reflector through the same hole that the bulb goes into, holding it from behind. That way, you won’t be blocking any of the light with your hands or the tinder. Point the reflector towards the sun and wait for your tinder to start burning.