Forensic, Alternate Light Sources

Alternate Light Sources

Alternate light sources (also known as forensic lighting), or the application thereof, are used by many forensic scientists to identify of evidences normally invisible to the human eye. A forensic light source consists of a highly adaptable lamp, capable of separating light into various wavelengths, allowing it to direct individual bands of light, both visible and infrared at a targeted area to reveal any unseen markings. There are three distinct types of light interactions that may occur when an object is seen through this method, those being: fluorescence, absorption, and oblique lighting. In fluorescence the light is reflected by the evidence, thus causing it to shine or fluoresce; in absorption the light is obviously absorbed by the evidence, thus causing it to be darker than its surroundings; and in oblique lighting, light is emitted at an object at low angles, thus causing it to give shadow and reveal small particles normally unseen.

Alternate light sources can be used for a range of things, anywhere from the collection of fingerprints, to the identification of bodily fluids, to distinguishing between authentic and forged documents. The most common use of alternate light sources is to collect fingerprints. This method can be 10-100 times more precise then the standard dust and lift method, and allows fingerprints to be taken off of a larger number of surfaces. Another use of alternate light sources is to spot bodily fluids such as saliva, semen, or blood that someone has attempted to cover up. Under normal conditions, most bodily fluids fluoresce under an ordinary UV light, but the background my also light up, giving a contaminated sample. A forensic light can be tuned so that the background is blocked out, leaving only the desired sample visible. Certain enzymes can also be sprayed to a given area; interacting with the hemoglobin found in blood and making it fluoresce even after cleanup has been attempted. An application of alternate lighting unknown to many is the use of it to identify forged documents. Inks, although same in color, vary their ingredients. A forensic light is capable of identifying these different ingredients, making it clear as to whether a document is the original or copy.

One court case, in which the use of alternate lighting was used to convict, was the case of the murder of Mary Stetson in Concord, New Hampshire,