For example if you buy a bright red car, in 5 years it is gonna be less bright red because it has been in the sun for a long time. Why is that?
In: Physics
Color molecules in pigments absorb some colors and reflect others. Red paint absorbs every color BUT red and reflects red wavelength, so that is what our eyes see.
The photons in light rays excite dye molecules and raise their energy. Most if the time they are unhurt, but sometimes it causes a chemical reaction that changes the electronic structure of the dye molecule. This then affects negatively the ability of the molecule to reflect and absorb light.
Red dye fades super fast because red is on the higher end of the UV scale and has more energy available for this process than colors like dark blue and indigo.
Black is interesting because (there are several different formulas for black dye) it starts out absorbing ALL wavelengths of light, but the dye molecules break down differently in sunlight. So a black item can fade toward red-orange, gray, green, etc.
Its mostly just sun rays that wash out colors. Natural things that are more UV resistamt will keep their color, but the sun rays essentially split the chemical bonds that make up the colors in the paint. However, for color to fully wash away takes a lot of time, just for the rays to make it all the way through. Depends on weight and material. Think about laser etching. It literally busts away the chemicals that ARE there, and leaves a byproduct over a good amount of time. Usually in the form of oxides or gases. The sun can drive a lot of weird things.
Ultraviolet radiation in sunlight is responsible for the fading of colors you’re describing. UV radiation is very energetic and destroys chemical bonds, which over time can change colors in objects it hits.
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