It’s time for one of B’s annoyingly pedantic and long-winded physics lessons.
Fluorescent colors are the result of visible light being emitted by the fluorescent surface that is in addition to the light being reflected by that surface.
Here’s how it works.
Our brains interpret different wavelengths (or frequencies) of the electromagnetic spectrum as different colors. We can only see a portion of that spectrum, the wavelengths that extend from violet through the other colors and ending with red.
However, there are wavelengths of light that we can’t see just beyond the parts of the visible spectrum that we do see. Just beyond the violet end, there’s ultraviolet. Just beyond the red end, there’s infrared.
When light hits an object, the surface of the object interacts with the light and can do one of three things. The light can bounce off the object. The light can pass through the object. Or the energy that makes up the light can be absorbed by the object.
Different wavelengths of light interact differently with the surfaces they hit. A green surface, for example, absorbs most light wavelengths while reflecting those wavelengths we call green.
Those wavelengths absorbed by the atoms in that surface cause the energy levels of those atoms to increase. This is why an object sitting in the sun heats up — it is absorbing much of the light and converting it into thermal energy.
An atom is composed of a nucleus and one or more concentric electron shells (or layers) surrounding the nucleus. It’s the outermost electron shell (the valence level) that light initially interacts with. If the resonating frequency of the valence electrons corresponds to the wavelength of light striking them, those electrons will absorb the light particle (a photon), upping their energy levels.
The electrons in each layer of the shell must maintain certain energy levels to maintain their positions in its shell. The electrons in the outer shells must have a higher energy level than the electrons in the inner shells.
Sometimes the absorption of a photon will provide enough extra energy to bump up the electron to a higher shell level, which creates an unstable electron arrangement. To correct this instability, the electron releases the energy it absorbs and falls back to its previous shell level. The energy that’s released is emitted as a new photon with a longer wavelength than the original photon.
This absorption of a photon of one wavelength (or frequency) and its subsequent release as a photo of a slightly different (usually lower) wavelength is called fluorescence.
When fluorescence occurs in most of the visible spectrum, we don’t notice it. If an orange photon is absorbed and subsequently emitted as a reddish photon, we don’t notice it. The object just appears redder than it would be without the fluorescence.
So with all that said, here’s what those fluorescent neon colors are.
When not-visible-to-us ultraviolet wavelengths of light interact with certain surfaces, those ultraviolet photons are absorbed and subsequently emitted as photons with lower wavelengths that we can see. The net result being a surface that appears brighter than expected. In other words, the ultraviolet-colored light that we can’t see is converted into light that we can see, which makes fluorescent, neon colors appear to glow.