highlighters can be useful in many situations, and when you highlight something, it is pretty surprising how bright they look. the other day i was wondering this exact thought, so i decided to look it up. when you see a color, the amount of light entering your eyes is usually the same as the amount of visible light of those frequencies the color reflects at you, however, with highlighter ink, this isn't the case. when you highlight something, apparently the color you see actually creates its own light. visible light, that is. As i found, highlighter ink contains an ingredient that takes invisible light like infra-red and ultraviolet that are emitted along with visible light in most light sources and turns them into visible light, making the ink look brighter than the light that shines on it. the fact that we know how to do this is amazing to me.