Often there is evidence indicating whether a vehicle's lights were on or off at the time of a collision — most commonly “hot shock” or “cold shock.” Hot shock is evidenced by deformation to the filament while it was on during an impact; cold shock by a brittle fracture while it was off. More complex issues may include circuit failures, damaged bulbs, improper wiring, and aged bulbs. A filament analysis can determine whether a vehicle's headlights, turn signals, taillights, and/or brake lights were on at the time of impact.