Why Are Lamp Examinations So Important? - Wednesday, 21st January 2009

Lamp examination during a vehicle inspection is both critical and highly informative. With proper inspection, a determination can often be made whether a lamp is on or off when a collision occurs because the filament may exhibit Hot Shock Deformation (HSD). This examination can also determine the principal direction of forces applied in the collision, and in many cases, whether a collision actually occurred.

What is HSD? We know from basic physics that Isaac Newton postulated that for every action there is and equal and opposite reaction. This is known as Newton's Third Law of Motion. Lamp filaments, when heated due to electrical current running through them, follow Newton's Laws of Motion. When the tungsten steel filament is heated, it becomes very pliable. During the collision, the filament stretches in a direction that opposes the applied force. This is HSD.

In a recent case, the forensic expert removed a turn signal lamp assembly on the front of a vehicle and a large chunk of brick fell out. According to the driver, his car was sideswiped by a hit and run vehicle. Since the contact area showed abrasive texturing and a piece of brick fell out of the lense housing, it was fairly easy to conclude that the damage was done when the vehicle struck a brick wall. What does this have to do with a proper lamp examination? Had the expert not taken the time to inspect the lamp, the brick particle would not have been discovered.

In another case, the rear lamp from a reverse indicator light showed moderate to severe hot shock deformation (HSD) in the filament. HSD only occurs when the filament is hot and a collision force is such that significant changes in acceleration occur. This evidence conflicted with the driver's statement. She stated that the collision occurred when she was struck from behind by a hit and run vehicle while stopped at a yield sign waiting for traffic to clear. The lamp examination and the contact damage pattern confirmed that the reverse lights were on when the reverse lamp filament was deformed.

While everything you need to know about HSD cannot be outlined in the space of this article, the lamp filaments closest to the contact area should be examined if at all possible. Whether HSD is present or not, you can learn more about the collision dynamics by performing a thorough lamp examination.