A simple, low-cost, and portable LED-based multi-wavelength light source for forensic application

Abstract

Forensic light sources (FLS) have been used frequently in crime scene investigation as a scanning tool for crime scene evidence, such as gunpowder residue, semen, bloodstain, saliva and urine. There were several FLS reported in literature, such as Polilight®, Lumatec Superlite 400, PolirayTM, Bluemaxx BM500 and high intensity LED. LED-based light sources are low in cost and flexible in design. Moreover, LED technologies have been well developed recently, where several types of wavelength LED can be used for light source design. From literature, near-UV light (300-400nm) and blue (450nm) light are useful for detecting semen, urine and saliva stains, while 415nm light is useful for bloodstains detection. In this paper, a simple, low cost and portable LED-based multi-wavelength light source for forensic application is proposed. The proposed multi-wavelength light source is able to supply near-UV, blue and 415nm lights from the same point of source and direction, without utilizing any light guide, such as optical fiber. Each type of LED array was mounted separately on the different surfaces of a holder. DC motor was used to rotate the holder for directing the selected LED array to face the object. The proposed design is low in cost, easy to be manufactured, user-friendly and comparable to the other expensive FLS, such as Polilight® PL500 and Crime-lite®2, in terms of detectable dilution of bloodstains.