optical density

Optical density is a measurement of the degree to which a refractive medium slows the transmission of light.

  • The optical density of a medium is not the same as its physical density.
  • The more optically dense a material is, the slower light travels through the material and so the higher the index of refraction.
  • The less optically dense (rare) a material is, the faster light travels through the material and so the lower the index of refraction.
  • A vacuum has the least density and so the highest speed of light.
  • Optical density accounts for the variation in refractive indices of different media.

https://en.wikipedia.org/wiki/Absorbance