Lecture 22 - Advanced Evidence Types Part 5

Question 1

Lightbulb filament as trace evidence

Answer 1

• ~10% of UK case load is glass evidence.
• Most significantly automotive glass, particularly headlamp smashes.
• Link hit and runs

Question 2

Most modern automotive light bulbs are one of three types:

Answer 2

• Halogen
• LED
• Xenon/High intensity discharge

Question 3

Halogen light bulbs

Answer 3

Most popular: Tungsten filament in glass tube with N/Ar

Question 4

LED light bulbs

Answer 4

• LED heats up
• Contain heavy identifiable metals
• They don’t have filaments so the traditional filament analysis can’t be done.

Question 5

Xenon / high density discharge

Answer 5

Heavy identifiable metals

Question 6

Lightbulb Tungsten Filament Analysis

Answer 6

• Tests to see if the lamp was illuminated at time of impact.
• Tungsten is rigid and brittle at ambient temperatures and ductile at incandescent operating temperatures.
• Oxidises when exposed to atmosphere at operating temperatures not when cold - microscopic analysis.
• Filament was OFF: No pronounced distortion.
• Filament was ON: Inertial force distortion on hot filament.

Question 7

Tattoos

Answer 7

• Can help track the movement of people and animals
• Can identify someone
• Description of tattoos is subjective and open to interpretation.
• Chemical analysis removes interpretation issues.

Question 8

Specialist pigments analysis

Answer 8

• Modern pigments are made of organic pigments (Azos etc.) or mineral pigments (TiO2, Iron Oxide etc.)
• Microscopic techniqes can be used for penetration depth and pigment distrubution.
• IR for organic binders and pigments.
• Raman for inorganic pigments
• SEM-EDX and XRF for elemental composition of layers.
• Pyrolysis-GC-MS