What is black light?
Visible light contains a wide spectrum of colours, as can be seen when looking through a prism. It starts with red and then goes through orange, yellow, green and blue to violet. Below red and beyond violet, however, there are still “colours” that are invisible to humans. The infrared (or IR, from Latin infra “below”) and the ultraviolet (or UV, from Latin ultra “beyond”). For many insects and other animals, these ranges belong to visible light.
Black light is the range of ultraviolet rays directly adjacent to the violet, also called UV-A. If it is produced artificially, it often also contains some bluish violet, as in this lamp.
The special properties of black light
Black light is invisible to humans, but it can make many substances that initially look inconspicuous glow in a surprising way. This process is called fluorescence. In addition to many minerals, plants and even animals, some chemical substances also fluoresce, e.g. the optical brighteners in detergents, the signal colours on warning signs or hazard warnings.
Where to use fluorescent light
– Banknotes have invisible security markings that can only be seen under UV light. This black light lamp is therefore also a fully-fledged banknote tester.
– The same invisible colour is used in the dome star chart “The Star Dome” by Atro Didaktik. Black light makes the dark stars and constellations magically light up, just like in a planetarium. Thanks to the zoom function, the whole dome can be illuminated or a single constellation can be highlighted.
– There are felt-tip pens with this colour; children can use them to write secret letters that can only be read under black light.
– Black light evokes a magical people in many minerals, including amber. That’s why amber collectors at the Baltic Sea always carry a black light lamp with them when they go to the beach at night.
– Black light makes unwanted insects visible, e.g. the scorpions common in southern countries.