The terms "transmission" and "penetration" are often used in the context of light interacting with different materials. While they are related, they describe slightly different aspects of how light behaves when it encounters an object.
Transmission refers to the ability of light to pass through a material without being absorbed or scattered significantly. When light is transmitted through a material, it continues to propagate in the same direction with little change in intensity or direction. Materials that allow light to pass through with minimal obstruction are often called transparent materials. Examples include glass, clear water, and certain plastics. In these materials, the atoms or molecules are arranged in a way that does not interfere with the light waves, allowing them to pass through relatively unimpeded.
Penetration, on the other hand, refers to the ability of light to reach or go into the interior of a material. It describes how deeply light can propagate into a substance before being absorbed or scattered. Some materials may transmit light to a certain extent but not allow it to penetrate deeply. For example, frosted glass allows some light to transmit through, but it scatters the light, preventing it from penetrating far into the material. In other cases, materials may absorb light to varying degrees, causing it to be attenuated and preventing it from penetrating very far.
To summarize, transmission focuses on whether light passes through a material with little obstruction, while penetration describes how deeply the light can propagate into the material before being absorbed or scattered. These concepts are closely related, and the extent of transmission often determines the degree of penetration in a given material.