The mirrored surface of a headlight reflector is described as “concave” in shape, similar to the interior surface of a rounded cup. It reflects light from a light-bulb that is mounted inside it and shines outward. Some of the newer headlights use a “convex” lens that transmits light through it. It is fashioned from a solid material such as glass or plastic that focuses the light from a light-bulb outward as well.In each case we reverse the process of light reflection and refraction to gather light from the sun into a single focal point in order to create an ember from tinder that we strategically place where the light-bulb was originally mounted. Simply point the reflector or lens toward the sun and minimizing the “hot spot” onto the tinder.
In both cases it’s good to know that automobile headlights can be used to start a fire in an emergency situation when you have sunlight by using either the reflective or refractive nature of it’s parts. Next time you pass a roadside, keep a look-out for these usable part and try it out for yourself!