Re: Please tell me how black light can be used to detect urine stains on carpet

Dear Nancy;

Urine stains fluoresce a dirty yellow color when under Ultra-Violet [or "Black"] light.This occurs with[I believe]the urine of all mammals - such as humans, cats, dogs, rats and mice [rodents].

This is due to the normal presence in urine of a group of substances called sometimes "bile pigments" such as urobiligen, urobilin, urochrome and some others.These chemicals are present from the breakdown of red blood cells and other nitrogen containing materials in the body. They are the cause of the normal yellow color of urine, and its fluorescence.

This property is used by police, etc. in looking for the presence of urine stains. Also, health inspectors, etc. use this to detect the presence of rats or mice or other animals in a grocery store, food warehouse, restaurant. Also it is useful to find where Fodo has left his trademark.

The test is quite easy to use. Turn off all room lights, turn on the UV light, look for a yellow fluorescence in the beam of the light. As with all tests, it is a good idea to try it first on a KNOWN urine stain , both wet and dry, so you know what to look for. In general, look in visible light for a yellow stain, then see if it glows yellow in UV light.

A problem is that many things fluoresce so that you may get a "False Positive" from some other substance. A different more elaborate laboratory type test would be needed to be 100% sure of the identity. Most laundry detergents leave clothes with a very intense white fluorescence which may drown out the weaker color from a urine stain.

Urine stains persist for years, unless the object is washed, so that you can't tell the age of the stain from the UV light.

The Black Light lamps are available in many novelty and party supply stores. Also I have seen them recently in Pet supply stores. A major supplier in the USA is:

UVP [Ultra-Violet Products}Inc.  3100 Walnut Grove 
Ave.  San Gabriel, CA 91776  [818] 285-2940
UVP Inc.