Fluorescence is the property of some materials to glow brightly when stimulated by high energy wavelengths of light. The glow of fluorescence is caused when the fluorescent material absorbs the high energy light and re-emits the light at a lower frequency rather than just reflecting the light. Fluorescent materials appear to "glow" under normal daylight near dawn and dusk, or on cloudy days, when the glow of the objects is not obliterated by intense daylight. You can stimulate fluorescent materials using UV, Blue, or sometimes even Green LED light.

It is important to note that this is different from "glow in the dark" materials which continue to glow after the light is removed. For fluorescent materials, once the light is turned off they do not continue to glow. They need the energy from the light to produce their interesting effects.

Here's a picture of some fluorescent and non-fluorescent objects under normal light. Note that they are all easily distinguishable, but nothing special seems to be happening.

Place your mouse over the photo to see what they look like under blue LED light.

Note which items glow brightly and appear to be their original color. The blue-bodied flashlight on the end reflects the blue light, but is otherwise unremarkable and appears the same color as the carpet. The end yellow, and middle green, OD and black-bodied lights just absorb the blue LED light. The bright yellow and orange lights take the blue light, absorb it, and re-emit it at a lower frequency. As a result they appear to be glowing and are their proper color under monochromatic blue light! Under normal daylight they do the same thing, especially under dim or twilight conditions. This is why fluorescent materials appear to "glow" and tend to be much more visible than their regular counterparts.

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