Actually yes they will fade - but it will take a long time and need directed and pretty unlimited exposure.
It is the UV in light which causes fading; the worst culprit for this is sunlight of course, then incandescent and fluorescent unnatural lights. But the latter two produce only a teeny tiny amount of UV [other wise they would be unsafe of course
] The only real light source which does not is LED - thats the only thing which wont issue UV and therefore wont fade something.
Black Curtains did a great experiment once with pink fading hair which actually showed how unnatural light hardly did anything to a fading pink hair colour.
So while it does fade things over time, its such a small amount I honestly dont think its something to worry about.