optical path length

Optical path length (OPL) is a measure of how far light travels through a medium, taking into account both the distance and the material's properties. It combines the physical distance that light travels with the refractive index of the medium, which indicates how much light slows down in that material. Thus, light traveling through denser materials like glass has a longer optical path length than the same physical distance in air. OPL is important in fields like optics and photography, as it helps predict how light will behave when passing through different substances.