It's your first chance in months to get out of Dodge. It'll be great to pack up some cold ones, a couple of fishing rods and some old clothes and escape to the country for a day or two. But as you leave the mercury-vapor-illuminated metroplex, you realize what you forgot--carrots, lots and lots of carrots, because you can barely see the road in front of you in the starlight of the countryside. Relax, it's not your failing eyesight. It's a burned-out headlamp.
For generations, American cars, and any car sold in the United States, had the same kind of headlight--a sealed-beam, either in a single or a quad arrangement. This fragile blown-glass envelope was filled with an inert gas and worked pretty well until it burned out. It had only modest performance, but the Department of Transportation mandated its use.
Most modern cars use what's called a composite headlamp--a plastic reflector bonded to a plastic or glass lens and fitted with a bulb. The bulb is of a quartz-halogen design. The "glass" bulb is actually made of silica quartz, which is highly resistant to heat. The filament is engineered to run at a much higher temperature, producing more light and heat. The silica envelope is filled with a mixture of halogen gases (iodine or bromine) to scavenge evaporated tungsten filament from the inside of the quartz, keeping each bulb's brightness constant until it fails.
Replacing a broken headlamp assembly is straightforward. Most of the fasteners and mounting hardware will have to be transferred to the new housing.