What is optical density?

The concept of optical density specifically refers to the measure of how much light is absorbed by a material as it passes through it. It quantifies the transparency or opacity of a substance when exposed to light.

In this context, optical density is calculated using the logarithm of the ratio of the incident light intensity to the transmitted light intensity. A higher optical density indicates greater light absorption, meaning that less light transmits through the material. Therefore, the correct interpretation of optical density relates directly to its role in measuring light absorption rather than the speed at which light or sound travels through a medium.

The correct choice clearly highlights the relationship between optical density and its effect on light passing through various materials. Understanding this principle is essential, especially in fields involving lasers and IPL, as it influences how different substances react to light and how effectively lasers can be utilized in various treatments.