Blacklights in a Cave

A Whole New Light

Written by Ashley

Want to experience the cave in a whole new light? Come and rent a blacklight flashlight to take with you on your cave tour. Watch our stalactites, stalagmites and other cave formations fluoresce under the glow of a blacklight. How is this possible you might ask, well let’s explain…

Blacklights emit ultraviolet or UV light, but what is ultraviolet light? Well, what we can see with our eyes is called visible light, aka “ROYGBIV” (colors of the rainbow). However, there is a light that is redder than red that we cannot see, so we call that infrared. Also, there is violet light that is more violet than what our eyes can see, so we call that ultraviolet or UV light. Since UV light is invisible, we call the bulbs that produce it “black” lights.

The ultraviolet light from the blacklights excites the electrons in the mineral calcite, the main mineral in all of our cave formations. When the “excited” electrons fall back to their natural state they give off energy in the form of light that we can see. This ability to absorb light and instantly release light back in a different wavelength (visible light) is a process called fluorescence.

Blacklight over formations producing a fluorescent blue light

Cave formations like stalactites, stalagmites, flowstone, and others are mainly made up of the mineral calcite, with the addition of varying amounts of manganese and iron. Fluorescence in minerals typically occurs when certain impurities known as activators are present. Manganese will help “activate” the calcite in the formations causing it to fluoresce. This is common among many of the formations in Cave of the Mounds. However, iron minerals are also present, which act as inhibitors to fluorescence. This is why certain parts of Cave of the Mounds fluoresce better than others.

Not all minerals will fluoresce. In fact, only about 15% of minerals have a fluorescence that is visible to people, and some specimens of those minerals won’t even fluoresce. For example, pure calcite will not fluoresce. Fluorescence usually occurs when specific impurities known as activators are present in the mineral.

Come check out this cool phenomenon for yourself and rent a blacklight for your cave tour.