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Comparison of Monochromatic Light Source and Banded Light Source for Detection of Evidence - Technology Evaluation

NCJ Number
234050
Date Published
Author(s)
National Forensic Science Technology Center
Agencies
NIJ-Sponsored
Annotation
This study compared the performance of monochromatic light sources and banded light sources for the detection of evidence.
Abstract
Anecdotal evidence during the past three decades suggests that monochromatic light sources and sources that emit specific bands of wavelengths do not accomplish the same tasks in the detection of evidence and that each search option has the potential to reveal targets missed by the other. The banded light source used in the testing came from the Polilight-Flare Plus, and the monochromatic light source was produced by the Coherent TracER Laser. The performance of the two types of light source was tested with evidence samples of fingerprints, semen, saliva, and blood deposited on a range of surfaces. Overall, no lighting option always produces the best results. The clarity of the target is dependent no only on its fluorescent response, but also that of the substrate on which it is found. In such a case, another light source that may not provide the best fluorescent response in the target evidence, may provide the best overall result for the evidence collection by exciting the substrate minimally or not at all. Polilight-Flare Plus (banded light source) was found to provide a wide range of evidence-detection options at substantive power levels and without requiring electrical power, thus allowing light examination at remote scenes. Photography is easily accomplished. The Coherent TracER Laser (monochromatic light source) is unsurpassed for the detection of untreated fingerprints. Also, its monochromatic output occasionally reveals evidence without as much background excitation as the Flare Plus. The laser is a powerful tool, but is currently limited to physical evidence revealed by 532nm emission. Monochromatice output at different points in the spectrum would excite other types of evidence not currently reached by the 532 nm version. Training requirements and health and safety issues are also discussed. Appended images of evidence produced by the two light sources
Date Created: March 23, 2011