An important use of titanium dioxide is in powder form as a pigment for providing whiteness and opacity to such products such as paints and coatings but also plastics, paper, inks, food and cosmetics, including most toothpastes. Titanium dioxide is by far the most widely used white pigment, it is very white and has a very high refractive index (n=2.4) — only surpassed by diamond. The high refractive index and bright white colour of titanium dioxide make it an effective opacifier for pigments, and (when deposited as a thin film), as a reflective optical coating for dielectric mirrors. One of its other major advantages is its resistance to discoloration under UV light. With titanium dioxide having the highest refractive index of all the colorless substances known, it provides the best light scattering ability as well as the best hiding power.