Opacity refers to the degree to which an object, area or surface obscures objects or space beyond.
- Different processes can lead to opacity including absorption, reflection, and scattering.
- An entirely opaque substance transmits no light, and therefore reflects, scatters, or absorbs all of it.
- When light strikes an interface between two media some light may be reflected, some absorbed, some scattered. The remainder undergoes refraction and is transmitted through the second medium.
- So, opacity is the measure of impenetrability to electromagnetic radiation, especially visible light by a material.
- An opaque object is neither transparent (allowing all light to pass through) nor translucent (allowing some light to pass through).
- Both mirrors and carbon black are opaque.
- Opacity depends on the wavelengths of the light being considered. For instance, some kinds of glass, while transparent in the visual range, are largely opaque to ultraviolet light.