DriveSmartBC - Post Crash Lamp Exams

[skidmark]

A tungsten lamp filament can tell a crash investigator a great deal post collision if you look carefully. Was it on or was it off? The outcome may mean that the headlights were on or that the signal light was never used. This information may be important to the outcome of the investigation.

A lamp that is on has a filament that is very hot and pliable. Subject it to a significant shock, such as the forces of a collision, it will stretch out inside the glass envelope, possibly even breaking. If it breaks, the broken ends will be pulled thin as the hot tungsten stretches.

If the glass around it breaks, little bits of glass will be seen melted to the filament if the power is withdrawn before the filament burns in the air. If not, the filament will be black and it's surroundings coated with the yellow-white powder of oxidized tungsten.

A lamp that is off has a filament that is cold and brittle. Subject it to shock and it will break leaving intact coils inside the glass envelope. The ends of the filament will be sharp and flat. This could also mean that the lamp had cooled below 400 degrees F prior to the shock.

Reference Links

[zulutango]

I remember a client telling me that his car had been parked in a mall parking lot all day, he came out and found the right side swiped and he even had the broken parts sitting next to the car. I pulled the park light bulb and found that it had heat stretch on the filament. Unless he had left his car with the engine running and the headlights on for 10 hours while he worked during the day, that was impossible. When I showed him the lightbulb he admitted that he had sideswiped a cement barrier at the end of a 4 lane, the night before when he had just had a fight with his girlfriend. He didn't make an ICBC claim and paid out the $8000 claim himself. Chalk up one for the science guy!

[jlenko]

You see this on cars at the wrecking yard... the filaments stretch out really nicely!

[Great68]

I guess with more HID and LED lamps on cars these days, it must be getting more difficult to use these investigation techniques.

[zulutango]

Just like it is measuring skidmarks from cars with ABS.

[sonick]

If you rear end somebody but their rear brake lights were not operational, who is at fault? Provided that you were going speed limit and following at a safe distance prior to the crash.

I've come across a few instances where the guy in front of me did not have working brake lights.

[Jeremy617]

if its at night, probably them. If its during the daytime, probably the person doing the rear ending? My guess anyways.

oddly enough I was driving behind 2 different cars yesterday for a bit, neither had any working brake lights.