Not an actual accident but I remember from the distant past that an accident investigator could tell if the old incandescent lamps were on at the time of an accident by the fact that the bulb filament was broken or not? True?, and how does an accident investigation determine if headlights are on with the new type of bulbs that do not have a filament?
Dark here today due to fog and thunderstorms and/drizzle, and saw anumber of vehicles driving without any lights on, hence the question.

Interesting question that reminded me of a police science class in the mid-1970s.

The instructor had received high level accident investigation and reconstruction training (Northwestern U?) and one of the things he said someone might research was whether it would be possible to determine if a headlight bulb had been on when broken and the filament then burned out due to the oxygen in the air or was turned on after the bulb was broken and then burned out. The point of course was the question of whether someone was driving with his lights off, got into an accident, and then turned them on.

That question was evidently unanswered at the time, and in thinking about it over the years I couldn’t think of a way to determine it. At this point the only thing that occurs to me is that if the bulb is broken and then the light is turned on, the filament might burn out with its temperature at a lower temperature than if it was already on when the bulb was broken. If someone claimed it was possible to tell the difference between the two situations, I’d be curious to know how that was determined.

Added: If the question is only whether the filament is broken but not burned out, then of course a unburned broken filament would demonstrate that the light had not been on when the bulb was broken.

^^^ The filament coils would be wildly deformed if lit upon impact. Lightly bent if burned out before impact. They could be compared to a similar bulb on the same vehicle or a sample bulb by the same manufacturer.

Yes. This worked for automobile accidents as well as the aviation industry. One other thing of interest was that in a high impact accident, the needles in the instrument cluster would leave marks on the panel upon impact marking their position upon impact.

I don't know if such a thing could be indicated by HIDs as they won't have any inertia driven components other than the glass that will shatter either way. It could be said that COBB LEDs may loosen under stress and thermal expansion. Purely a guess on my part.

Going back a lot of years, but I seem to recall that even if the bulb didn't break, you could tell if it was illuminated at impact. The filament would distort at impact differently if it was white hot vs cold.

quote:

Originally posted by .38supersig:
^^^ The filament coils would be wildly deformed if lit upon impact. Lightly bent if burned out before impact. They could be compared to a similar bulb on the same vehicle or a sample bulb by the same manufacturer.

Yes. This worked for automobile accidents as well as the aviation industry. One other thing of interest was that in a high impact accident, the needles in the instrument cluster would leave marks on the panel upon impact marking their position upon impact.

I don't know if such a thing could be indicated by HIDs as they won't have any inertia driven components other than the glass that will shatter either way. It could be said that COBB LEDs may loosen under stress and thermal expansion. Purely a guess on my part.

HID lamps do have components inside of them, shake one.

LEDs are not really affected by vibration or sudden changes in momentum.

Does the car's computer know now if the lights are on or off and store that data?

It seems like it could know, but I don't know if they do and if they store that information.

The event data recorder will probably show it but you'll need a court order to read one.

Most modern cars have a "black box" for vehicle systems that can say if lights were on, brakes were applied, speed, etc.

It is easier to tell if the driver was lit at the time of impact.