Friday's Ask the Experts: Black lights

I strongly disagree with the statement that a black light will not detect urine on the surface of a carpet after it has been cleaned. Some fluorescence will still be seen after cleaning. It takes very little salt or protein to create a glow under the proper UV (black) light. Cleaning agents will dissolve the urine. Extraction may remove most of the water, urine and spent cleaning solution, but some is still left behind. In fact, as the water evaporates, what was dissolved in the water is left on the surface. So the cleaning process can result in some of the urine that was below the surface now being left on the surface. This is similar to the process the wicks soils to the surface as a carpet dries following hot water extraction. For an analogy, consider a CSI style crime show. The criminal may try to cover his tracks by cleaning the scene of the crime. But the CSIs using UV light can locate even the smallest amount of blood or other body fluids. The same is true of even small traces of urine being visible under the proper UV light. Scott Warrington Director of Technical Support Interlink Supply / Bridgepoint Systems