 Welcome to this activity, Forensic Lamp Examination. Lamps can have a single filament or dual filaments. Any or all of these filaments can display evidence to suggest whether or not the lamp was on. When examining a vehicle that was involved in a collision, evidence in automotive lamps can help you to assess whether or not the lights were being used. In particular, it is the internal filament that may show evidence of use. The filament, which is made of tungsten, is supported by two posts inside the bulb. When an automotive bulb is new, the tungsten filament appears bright silver in color. Then, as the lamp is used throughout the vehicle's lifetime, it starts to appear rough and pitted. However, it will remain silver even as it ages. When power is provided to a filament, the filament heats to about 4,000 degrees and gives off heat and light. As it heats up, the filament becomes ductile. That means an outside force could change the filament's form without the filament breaking. If a lamp is on when a vehicle is involved in a crash, the filament may stretch and deform. When the car or truck stops suddenly, the bulb itself also stops. However, the filament may keep going until it stretches out. When the bulb is later examined, the filament will appear stretched and distorted. However, it will still maintain its silver color. When a vehicle is slowed or stopped suddenly from a high-speed crash event, a cold filament may break apart as it continues forward. The filament will be in one or more pieces that can usually be found in the bulb's glass envelope. All components will be silver in color. When examining the pieces, there will be no sign of melting or heat. The break points will likely be jagged. As the cold filament continues forward when the vehicle stops suddenly in a crash, it may break away from its post. The color will remain silver, and pieces may be found in the glass envelope. When the lamp is later examined, small pieces of the filament may be seen in the bulb. Again, the filament will maintain its silver color. In an air-evacuated glass envelope, oxygen is removed and replaced with an inert gas. If the envelope breaks with a hot or incandescent filament, the new presence of oxygen will also leave evidence. It should be noted that in both of these examples, the glass envelope surrounding the filament remained intact. This envelope keeps oxygen away from the filament. If the envelope breaks during a crash and the lamp is on, the onrush of oxygen will cause the filament to burn. Note the black discolored break filament and the yellowish powdery substance on nearby surfaces, including the tail lamp filament. The burning filament will produce tungsten oxide, which is a yellowish powdery substance that will stick to nearby surfaces. The filament will immediately turn black in stark contrast to its usual silver color. In addition to the blacken filament and presence of tungsten oxide, glass pieces from the envelope may fuse to the hot filament. While a microscope is often needed to view this evidence, it is sometimes visible to the naked eye. If the glass envelope breaks on a lamp that is not on, the filament will remain silver. The filament may also be pulled or stretched by striking components, but it will not be stretched in the same manner as a hot filament. Again, it is the silver color that helps to designate a cold filament. When examining lamp evidence, never turn on the lights to see if they work. This could cause filament evidence to be destroyed. Rather, examine each bulb individually for evidence of hot shock, cold shock, hot break, and cold break. These observations will assist in determining whether or not the vehicle's lamps were being used at the time of the collision. You have completed this activity, forensic lamp examination.