Optical density is a measure of how much a material resists and slows the transmission of light.
- The higher the optical density of a material, the slower light travels through it.
- The lower the optical density of a material, the faster light travels through it.
- A vacuum is not a medium and has zero optical density.
- Light travels through a vacuum at the maximum possible speed of light which is 299,792 kilometres per second.
- Optical density and refractive index are related properties.
- In general, materials with higher optical density tend to have higher refractive indices and vice versa.
- The greater the difference in refractive index between two materials, the more they will bend light when they come into contact.