Vehicle lamps are examined in an effort to determine if a lamp was ON or OFF at the time of a collision. The ON or OFF condition of the lamp can assist in accident reconstruction and determination of fault.
Determination of ON or OFF is generally based on how the impact from the collision affects the configuration or condition of the filament inside the lamp.
A hot filament that was ON at time of impact. The filament has been stretched and bent, but did not break.