Why do red sign graphics fade first?
This OSHA safety sign isn’t far from our business. You’ll often see signs like this where the red is almost gone and the other colors aren’t faded too bad. So, what are the reasons why red fades first?
First, lets define UV light. Ultraviolet (UV) light is an electromagnetic radiation with a wavelength from 400 nm to 100 nm (shorter than that of visible light). Lets also assume that UV light is what causes fading. UV light has a shorter wavelength than visible light. Light with a shorter wavelength has more energy than light with a long wavelength.
Short wavelength visible light (like blue) is more toward the UV end of the visible light spectrum (*see spectrum image) so therefore it is a shorter wavelength and has more energy. Longer wavelength visible light (like red) is more toward the the infrared end of the visible spectrum and therefore has less energy. Because of their greater energy, the shorter wavelengths of light cause more “bleaching” of the pigments in the paint and more fading. So, why would light with a very short wavelength effect RED more than Black? The main reason has to do with what light is reflected by each color and what light is absorbed. Red ink or pigment reflects the long wavelength light (like red) and absorbs the more destructive higher energy shorter wavelength light like the blues and greens.
Silver, Blue and white graphics will reflect the short wavelength colors better (and therefore reflect more UV light) so they’ll fade slower.
I’m not an expert on how light affects pigment, but this is what I’ve compiled based on my research and discussions with others. Now you’ve got an answer when a customer asks why his red sign faded quicker than his blue sign.