Fluorescent material absorbs invisible ultraviolet light from sunlight, and through special pigments, appears brighter to the wearer and viewer. This material only functions when there is natural sunlight. Fluorescent colors provide the greatest amount of contrast against most backgrounds and so when deciding on what colour hi-viz you should wear, you must consider your surroundings and the colour that will reflect the most light in particular environment. The 3 colors, approved in the EN ISO 20471 are Yellow, Orange and Red.