Light bulb test?

Question

Friend was asking me because I know a little about cars but supposedly the officers performed a light bulb test on his car to test whether or not the headlights were on before the accident. The only way I can think of doing it is to actually touch the filament of the bulb to see if it was warm (indicating it was on) or off but that doesn't seem very scientific or as a solid proof they were on or off.

Does anyone know how such tests are performed on the vehicle? Explain in detail if you could. Thanks!

It is of course possible that the whole head light assembly is completely smashed if an accident is head on and the speed is fast enough. Is there still a way to test for lights other than the filament if whole assembly is wrecked?

Answer 1

If a light was on before an accident it will have heated up. This takes very little time. This heat will make the filament more flexible.

You can look into the light and tell by the stretching/breaking of the filament if it was on when the accident occured. It is actually very reliable.

Answer 2

If the glass on a light bulb is broken and the light it on or turned on, the filament will break. This is because a light bulb is sealed so no oxygen is inside. If the glass breaks, then oxygen is introduced. If the light bulb was on during the accident, as soon as the glass was broken, the filament would break. If the light was off, then the filament will not break (unless the light is turned on anytime after).

Answer 3

Aviator is pretty close, but the filament can break in a crash, but if the light was on the oxygen coming from outside the bulb, will oxidize (burn ) the filament if the lights were on, it will not with the lights off

Answer 4

These first two guys answered your question correctly.