Alternate Light Sources

Question 1

What are alternate light sources?

Answer 1

Equipment used to produce visible and invisible light at various wavelengths

Question 2

Describe the relationship between wavelength, frequency, and energy.

Answer 2

Shorter wavelengths = higher frequency = more energy
Longer wavelengths = lower frequency = less energy

Question 3

What type of light is considered the forensic spectrum?

Answer 3

UV, visible, infrared

Question 4

What is the electromagnetic spectrum?

Answer 4

The range of all electromagnetic radiation

Question 5

What type of radiation is not visible to the naked eye?

Answer 5

Below 400 (UV), above 700 (IR)

Question 6

What colour of light is 450 nm?

Answer 6

Blue/purple

Question 7

What colour of light is 520 nm?

Answer 7

Green

Question 8

What colour of light is 630 nm?

Answer 8

Yellow

Question 9

What colour of light is 720 nm?

Answer 9

Red

Question 10

What are the three things that could happen after light strikes an object?

Answer 10

Reflection
Transmission
Absorption

Question 11

What does the manner in which visible light interacts with an object depend on?

Answer 11

Frequency of the light and the nature of the atoms of the object.

Question 12

Describe light reflection.

Answer 12

Occurs because frequencies of incoming light waves don’t match natural frequencies of the vibrations of the atoms in the object.

Question 13

Describe light transmittance.

Answer 13

Occurs because frequencies of incoming light waves don’t match natural frequencies of vibrations in the object; light passes through the object.

Question 14

Describe light absorption

Answer 14

Occurs because frequencies of incoming light waves match the natural frequencies of vibrations in the object; light is absorbed by object and converted to another form of energy.

Question 15

Describe the forensic aspect of the ALS theory.

Answer 15

Interested in the re-emission of absorbed wavelengths or the fluorescence.
Wavelength of light that is emitted is of a longer wavelength than the absorbed radiation

Question 16

Describe the science behind fluorescence.

Answer 16

Radiation energy is absorbed by an object
Electrons become excited from the ground energy state to high energy levels
Electrons eventually relax back to ground energy level
Energy is losy
Remaining energy is emitted
Stokes shift

Question 17

What is Stokes shift?

Answer 17

Refers to the difference in the peak height between the admission (fluorescence) and excitation (absorption) wavelength

Question 18

What is an ALS used for at a crime scene?

Answer 18

Locate evidence
Visualize evidence
Enhance evidence and details

Question 19

What are the benefits of using an ALS?

Answer 19

Non-intrusive
Doesn’t degrade, alter or damage evidence

Question 20

What types of evidence fluoresce? (7)

Answer 20

Sweat
Saliva
Semen/vaginal fluids
Trace (hairs/fibres)
Volatile organic compounds
Bone/teeth
Fingerprints

Question 21

What type of ALS is considered to be the most versatile for crime scene work?

Answer 21

450 nm ALS

Question 22

What are the three types of filters used with ALS?

Answer 22

Exciter filter
Barrier filter
Narrow band pass filter

Question 23

What is an exciter filter?

Answer 23

Used on flashlight; allows passage of a single band of wavelength while blocking all others

Question 24

What is a barrier filter?

Answer 24

Used on goggles, camera lenses; isolates the desired fluorescence while blocking all other reflected wavelengths

Question 25

What is a narrow band pass filter?

Answer 25

Allows for further isolation of desired fluorescent wavelength from a busy background that also may fluoresce.