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• Appraisers use them to detect forgeries of antiques. Many paints today contain phosphors that will glow under a black light, while most older paints do not contain phosphors.
  

• Repairmen use them to find invisible leaks in machinery -- they inject a little fluorescent dye into the fuel supply and illuminate it with a black light. For example, they might detect an invisible air conditioner leak by adding fluorescent dye to the refrigerant. Black lights can be used to detect counterfeit bills.

• Law enforcement officers can use them to identify counterfeit money. Many countries include an invisible fluorescent strip in their larger bills that only shows up under a blacklight.

Image ModifiedFigure 7. UV light for law enforcement officers

• Amusement parks and clubs use them to identify invisible fluorescent hand stamps for readmission.

• Forensic scientists use them to analyze crime scenes. To pick out fingerprints, for example, they often dust with fluorescent dye under a blacklight. This makes it easier to pick the fingerprints out from surrounding dirt. Black lights can also identify bodily fluids that naturally fluoresce.

Figure 8. UV light in criminal investigations

Most of these uses, as well as dozens of others, follow a common theme, the black lights make the invisible visible or isolate one specific substance from everything around it. When you think about it, there are dozens of situations where you could put this phenomenon to work. The applications are potentially endless!

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