UV-A is also emitted from specialist lamps and are sometimes casually referred to as ‘dark lights’. UV-A causes fluorescence in certain substances e.g. rocks and clothing that cause funky, bright colours in clothing at night clubs. UV-A light sources are successfully used by NDT industries (non-destructive testing) to find fine cracks in a metal using fluorescent dye, for example.
UV-A LEDs are already available on the market in the form of UV-A torches. UV-A light sources may also find use in causing fluorescence on bank notes to check if they are legit or may be applied for curing of glues and resins in certain manufacturing industries. UV-A light sources are also used in mineralogy, which can cause fluorescence in certain rock types that enable identification.
Fluorescence in rocks is rather spectacular in the remarkable bright colours produced in a dark room or outdoors at night – this is the same principle that fluorescent bulbs work on. Certain insects may also undergo a brief colour change when exposed to UV-A radiation.