The refractive index is a way of measuring how lights behaves through a certain medium. This number gives an indication of how light reacts and how light is reflected. Manufacturers use (among other things) this as an indication of how light is reflected by a protective product and how that will make the surface look.
Why a refractive index
Light behaves in a certain way, this way is known to science. We can use this knowledge to predict what light will do when it goes from travelling through gas (air) and solids or liquids. The behaviour of light in this situation gives an indication of how a surface will look. An object can look glossy, glassy, have a warm glow, matte and several other ways. This is partially determined by the way light behaves.This particular behavior is also used to show the difference a protective product can make. The refractive index is measured before the product is applied, and afterwards. If the refractive index has changed, this difference is used to determine the effect the product has on light.
How light refraction works
In simple terms, light changes its way when changing from one medium to another medium. When light changes from going through air to clear coat (transparent solid), the light changes speed and direction. When it hits the colored coat underneath, it get reflected back again. The reflected light is affected again when it goes from the clear coat into the air again. When a product is applied on top of the clear coat, the light is also affected when it goes from air into the product, and then again when it goes from the product into the clear coat. The changes the light goes through determine how a surface looks.
Types of reflection
The refractive index is affected by several different variables. For example; a wax is made from several ingredients that are not completely transparent, the wax, the dye and several other ingredients are not 100% transparent. The final product is also not completely transparent. This means that the final microscopic layer of wax (after buffing) is also not 100% transparent. This microscopic layer has a very minimal effect on light, but enough to be measured. In some cases even enough to have an effect on the type of shine that is achieved.
Ceramic coatings generally leave a thicker layer then wax, and are almost 100% transparent. They have a different effect on light which causes to create a different type of shine.