he simplest test that crime scene investigators use to detect bloodstains that are not clearly visible is an alternate light source (ALS) such as ultraviolet light. This method is especially helpful when the stain is on a dark background [11]. An ALS can direct attention to a latent stain at a crime scene, and then further presumptive tests can be utilized to form more conclusions about any body fluids that are present. A versatile light source product known as Polilight® contains a range of wavelengths and can even reveal stains covered by paint [19]. These light sources must be used with caution, however, since certain ultraviolet wavelengths can damage the DNA evidence in a sample. One study found that exposure of 30 s or more to 255 nm light damaged the DNA enough that none was detected during polymerase chain reaction – short tandem repeat (PCR-STR) quantification and amplification [20]. Another experiment found that restriction fragment length polymorphism (RFLP) patterns only weakened and were not falsified with exposure to UV light up to 5 days, but the wavelength used was not specified [21].