Headlamp Analysis - Headlights on or off?

When a headlamp is illuminated, the coiled tungsten filament is heated by electrical resistance to a temperature of 4500 degrees F.  At this temperature, the filament emits radiation in the form of white light.  If the glass covering is broken during a collision, several things are likely to happen.  The "shock" or impact which breaks the glass will cause the headlamp to move violently.  When this occurs, there will be inertial loads imposed on the filament coils.  If the filament is cold, it will sustain very high inertial loads without deforming the filament coils.  However, when the filament is white hot, the metal is relatively malleable and most impacts which break the glass will also deform the filament.  This results in a filament which has bends, bows or other non-uniformity in the coils.

Headlights on or off?  

Deformed Filament "Lights-ON"

Deformed Filament

"Headlights On"

Headlamp Filament

Microscopic Examination

Deformed Filament