The Fluorescent Difference
Why do fluorescent colors appear so different? First, it is because fluorescent colorants are very intense. But fluorescent colorants also have a second unique property not associated with “normal” colors. This extraordinary property allows them to take some of the invisible short-wave light/energy and re-radiate the energy as longer, visible light waves. Fluorescent colorants, in effect, cause a “shift” from shorter invisible radiation to visible light at longer wavelengths. In simple terms, such colorants may be thought of as “more efficient” than ordinary colors at utilizing the light/energy that reaches them.
Particularly effective for traffic signing
Because the natural light that reaches us at dawn, during evening twilight, and through overcast skies contains more of the shorter, blue-end waves, fluorescent colors appear even more visible to the human eye under those conditions. This is why fluorescent traffic signs are most effective during adverse daytime driving conditions.