Properties of Light Forensic Light

1. Properties of LightForensic Light Test: Friday Oct. 7 *properties of matter *density *properties of light *fracture patterns

2. Properties of light • Light waves: • Differ in frequency and wavelength • speed of light—299,792,458 m/s

3. Electromagnetic spectrum

4. Properties of Light • Dispersion: • Process of separating light into its component colors (ex: prism) • As visible light passes through the glass of a prism each color composition of light is slowed to a speed slightly different from the others. • Causes each component to bend at different angles as it emerges from the prism

5. Properties of Light • Refraction: • The bending of light waves because of a change in velocity

6. Properties of Light • Refractive Index: • How much an object slows the speed of light • Ratio of velocity of light in a vacuum to its velocity in any medium RI = velocity of light in vacuum velocity of light in medium • Varies with temperature of substance and wavelength of light passing through it

8. Forensic light and glass • Forensic scientists use two methods when analyzing glass • Determining the density of the shard of glass in question • Determining the refractive index of the shard in question

9. Forensics Light and Glass • Refractive Index of Glass: • A piece of glass in question is immersed in a liquid medium whose refractive index is adjusted until it equals that of the glass particles • At this point (match point), the observer notes the disappearance of the Becke line • Becke line—halo near the border of glass particle that is immersed in a liquid of different refractive indices • The Becke line disappears when the medium and fragment have similar indices

10. Becke lines

11. Each of these three identical jars contains a glass stir rod. One jar is empty, and the entire rod is visible. The second jar contains immersion oil, which has the same refractive index as glass, making the rod invisible. The third jar contains water, and the rod appears bent.

12. Forensic Light sources • Forensic light source is made up of a powerful lamp containing UV, visible, and infrared components of light • 3 techniques: • Fluorescence (evidence glows) • Absorption (evidence darkens) • Oblique lighting (small particles of evidence revealed—hair, fibers)

13. Forensic light uses • Detecting latent fingerprints • Detecting bodily fluids • Hair and fibers • Bruises, bite marks, pattern wounds • Questioned documents—forgery • Gun shot & explosive residue • Bone fragments, tire tracks, shoe prints, drugs

14. Latent fingerprints

15. Bodily Fluids • Semen, saliva, and vaginal fluids • all glow • Blood • does not glow—it appears black Semen Saliva

16. Documents--Forgery In works of art, modern paint will fluoresce or glow under a black light, older paints will not. Thus, pictures that have been "touched up" with modern paint will glow. Bank notes also incorporate fluorescent dyes, which glow under exposure to UV illumination. The color and location of the security thread in US dollar bills are unique to the value of the bill.

17. Gun shot residue Under infrared light

18. Bones UV fluorescence of burnt bone Bone fragments