Forensic Sciences
What is a Forensic Light Source
A forensic light source is a crime scene investigator’s and lab technician’s tool for enhancing observation, photography and collection of evidence including latent fingerprints, body fluids, hair and fibers, bruises, bite marks, wound patterns, shoe and foot imprints, gun shot residues, drug traces, questioned documents, bone fragment detection, etc...
- More sensitivity than traditional methods thus increasing the amount of evidence uncovered and the quality of the evidence photographed and collected.
- A traditional forensic light source is made up of a powerful lamp containing the ultra-violet, visible and infrared components of light. It then filters down the light into individual color bands (wavelengths) that enhance the visualization of evidence by light interaction techniques including fluorescence (evidence glows), absorption (evidence darkens), and oblique lighting (small particle evidence revealed).
- The use of fluorescent enhancement processes that compliment a light source greatly increases the types of surfaces from which a latent fingerprint can be detected.
- Using traditional methods, fingerprint evidence on these and other types of surfaces may go undetected or even dismissed because they could not be detected with enough detail.
- Works well on textured surfaces....
Different wavelengths are required for processing different types of surfaces making a forensic light source with tunable or multiple wavelengths a coveted tool for any crime scene investigator. In many cases the background surface will also glow under light source illumination. In these cases it is necessary to tune to a color band (wavelength) of light that causes the print to glow and not the background. The quality and quantity of evidence revealed is proportional to the output power and the extent of wavelength tunability of the light source. Since fluorescent techniques are very sensitive, only trace amounts of fluorescent powder are required when dusting for prints at a crime scene . It therefore leaves the scene much cleaner than when using black powder.
- A crime scene investigator can narrow down the specific locations of stains for collection instead of testing entire, large pieces of evidence such as a mattress, a carpet, a sheet, an article of clothing, etc...
- The dried body fluids will actually glow under the light source illumination. Although the body fluids will fluoresce under an ordinary UV black light, many articles on which you would find them including clothing and sheets will also glow and deter their detection.
- It is therefore necessary to tune to visible wavelengths to eliminate the background interference.
- The more powerful and more tunable your light source, the more evidence you will uncover. Although blood does not glow in the visible range, it has a unique wavelength under which the blood stain will darken to enhance its contrast by approximately 4 times. This is most effective in photographing blood prints because more of the detail of the blood print will be revealed by the enhanced contrast.
- Bite marks, bruises, and other pattern injuries can be identified on living and deceased victims using 450-nm (blue) illumination.
- Complimentary Light Photography by using the appropriate wavelengths and filters, the background image and unwanted colours can be removed, allowing the trace evidence to stand out.
- Inks have different formulations, even within the same apparent color type.
- A tunable forensic light source can be used to identify slight variations in ink type by viewing ink responses as the color of the light is tuned through the visible and infrared regions.
- These differences can be observed with a forensic light source.
| Forensic Applications Addressable with LED Technology. |
| Ultra-Violet |
<400nm |
UV sensitive powder & dyes. |
| Violet |
400-430nm |
blood stains and gunshot residues |
| Blue |
430-470nm |
Locates semen, saliva, urine,and blood. Detects and enhances bite marks and bruising. Body Fluids
|
| Blue/Green |
460-510nm |
Increases contrast of latent prints on a variety of surfaces. Superglue Fingerprints
|
| Green |
500-550 nm |
DFO 1,8-Diazafluoren-9-one Fingerprints |
| Yellow |
550-600nm |
Reduces background fluorescence from surfaces treated with DFO. Is ideal for examining questioned documents
|
| NIR |
700-1000nm |
Gunshot Residue Questioned Docs | |
Advantages of LEDs for Forensics
Wavelength Coverage UV à Visible à NIR
- Can be achieved in LEDs and lamps.
- UVA – now readily available in LEDs.
- UVB/UVC in research – efficiency/reliability improving
- NIR used for camera night illumination
- System choice with LEDs – can use single colour interchangeable light source or combine colours in a single light source and select a wavelength or combination of wavelengths in simple manner.
Selective
- Filters used for lamps – throwing away light & generating heat in lamp housing
- LEDs – only emit at discrete wavelengths and are therefore most efficient.
- Rapid wavelength switching possible – interaction with digital image processing
Lightweight & Portable
- Large lenses not necessary
- Filters not necessary
- Heat is generated in LEDs through back of LEDs
- Lenses and housing do not generally get hot
Robust
- LEDs do not shatter like lamps
- LEDs do not break suddenly but degrade over a long time period.
- LEDs can live for > 50,000 hours. Average lamp life 300 hours.
- Can be used underwater or in very wet environments – low voltage – safe.
High Power Flexible Systems
- Form spotlights just like lamps, ringlights for microscopes and can also be built into strips or panels for large area illumination
- No wasted light