Fluorescent describes something that glows with an unusually bright, almost electric-looking color when light hits it. You've probably seen fluorescent yellow safety vests that construction workers wear, or fluorescent pink highlighter markers that make text practically leap off the page. These colors seem to glow from within, catching your eye even in dim light.

The word comes from a scientific property: fluorescent materials absorb invisible light energy and release it as visible light, making them appear brighter than ordinary colors around them. This is why fluorescent colors look so intense and vivid.

Fluorescent lights, those long tubes you see in schools and offices, work the same way. Electricity causes a gas inside the tube to produce invisible ultraviolet light, which hits a fluorescent coating on the inside of the tube. That coating then glows with bright white light.

In nature, some jellyfish, coral, and even certain scorpions are fluorescent: they glow with surprising colors under ultraviolet light. Scientists have discovered fluorescent proteins in these creatures and now use them in research to track cells and study how living things work.

When something is so bright it almost hurts to look at, people sometimes call it fluorescent even if it's not technically fluorescent: “His fluorescent orange shoes were impossible to miss on the soccer field.”