Opacity is considered what type of measurement?

Opacity is classified as an indirect measurement because it quantifies the extent to which a material obstructs the passage of light rather than providing a direct measurement of a physical dimension or quantity itself. In this context, opacity is determined by evaluating the amount of light transmitted through a sample relative to the amount of light that is initially present.

This approach relies on inference, as the measurement of opacity does not directly measure a specific physical characteristic like length or mass, but rather derives its value from the interaction of light with the material. The measured opacity reflects the properties of the material in relation to light, making it inherently an indirect way of assessing how much light passes through or is absorbed. Understanding this indirect relationship is central in fields that require analysis of material properties using light, such as in various scientific and engineering disciplines.