Motorcycle Headlamp Filament

A fifty (yes, 50) year old Harley Davidson motorcycle (antique) was being driven near the city limits of a rural town.  A pickup truck reportedly pulled in front of the motorcycle and a collision ensued.  The truck driver claimed that, although it was required by law and it was dusk, the motorcycle headlamp was not operating. The motorcycle headlamp is shown in Photograph A.

Photograph A  Overall view of fifty year old Harley Davidson motorcycle headlight.  Note the headlamp is still intact.

Visual examination of the headlamp indicated that the headlamp bulb was still intact.  That is, the headlamp bulb, located at the base of the headlight was still intact.  A close-up view of the headlamp bulb is shown in Photograph B.

Photograph B  Close-up photograph of headlamp bulb with curved filament denoted with arrow in lamp base.

In Photograph B a portion of the headlamp filament is noted at the base of the headlamp bulb.  An arrow denotes the curved filament. A new headlamp bulb and filament are shown in Photograph C.

          Photograph C

It is clearly evident that the new headlamp filament is straight and un-deformed.  An arrow in Photograph C denotes the straight, un-deformed filament.

When a headlamp is on, the filament will have a temperature of over 5000°F.  If the velocity of the filament is suddenly changed, i.e., by an impact, the filament will deform (bend) before breaking.  If the filament is cold, no filament deformation will be noted.

A report highlighting the hot filament deformation was issued and the matter was resolved.