High-intensity discharge (HID) headlamps are increasingly being employed in place of incandescent headlamps for automotive forward light systems. While the post-impact analysis of incandescent bulbs and filaments to determine the power state at impact is a mature field, there is little information currently available in the literature that can be used to determine if an HID headlamp was powered at the time of impact. HID headlamps differ significantly both in architecture and operation compared to incandescent headlamps; the light is produced by passing electrical current through a gas and generating a luminous arc, rather than by resistive heating of an incandescent filament. Though the filament examination techniques often used by accident investigators cannot be directly applied to HID lamps, the unique features of these lamps provide opportunities for new methods.
This paper presents the results of stationary impact tests performed on a representative HID lamp. Several characteristics are described that can be used to determine whether the lamp was powered at the time of impact. Techniques utilized during the examinations included visual, optical microscopic, and scanning-electron microscopic examination of the lamp arc tube and electrodes. These methods all require the arc tube of the lamp to break during the collision.