What is it that makes a color react so well with a black light? I think it is called Day-Glo in some places. I want the local discount store to make me a few gallons of it so i can paint my house this sort of color. The only kind that I can find is in spray cans and that would run about half a million bucks for my 700 sq ft. house, and I want to get the gallon cans for $10 with free color added! Will they have the necessary additives, or is that why the price is so high? What is the additive?
“Day-Glo” is a trademarked name for that brand of fluorescent paint. They get touchy when their name is bandied about as a synonym for “Fluorescent”, because they don’t want to have their precious brand name reduced to a generic term that anybody can use. That’s what happened to “cellophane” and “aspirin” and “zipper”. Look in the pages of Writer’s Digest to see full-page ads from companies just begging you to avoid statements like “Let’s Xerox it”, and to use patently unearthly sentences like “Let’s make a Xerox brand photocopy of it.”
There are other brands of fluorescent paint. What happens is that the paint absorbs a photon of short wavelength light (usually ultraviolet), then re-emits a photon of visible light (at adifferent wavelength). This differs from ordinary paint, where light is merely reflected and there is no wavelength difference (technically called a “Stokes Shift”) between incident and emitted photon.
This may surprise you- you might be incredulous. If you’ll recall, pure white, such as a clean white shirt, or a tablecloth, lights up in UV light. You don’t pay much attention because it’s just white. The only thing special about day glow paint is that there are no black or gray pigments, only a mixture of the color plus white. I’ve consulted with chemists and physicists about it. There are materials that do fluoresce, absorb light at one wave length and emit it at another, such as some minerals and some organic compounds but that’s not what is in day glow paint. That doesn’t mean it’s simple to create those colors. There are thousands of pigments that contain black and grey. It’s very complicated to get a pigment that reflects only white and colored light.
That’s a fine job of taking a quote right out of Wikipedia. Look hard at what I’m saying here. There are light reactive compounds, they absorb uv and emit at a different wave length. That’s luminescence. That’s not what I’m talking about. You take any piece of white copier paper in a dark room and shine a uv light on it and it appears to be emitting light. Try it.
Which is true, but it’s exactly the same thing you describe at the beginning of your post – again it’s fluorescence. Here, fluorescent compounds are added to make “white” objects look even more dazzlingly “white”. It’s a trick that relies on the fact that we observe blue parts of the spectrum as brighter than yellow or red parts of the spectrum.
