Transparency
The light can penetrate through any transparent or translucent objects because the light always travels in a straight line. Materials like air, water, and clear glass are called transparent. When light encounters transparent materials, almost all of it passes directly through them. Glass, for example, is transparent to all visible light. Translucent objects allow some light to travel through them. Opaque objects . Materials that do not allow light to pass through are called opaque materials. Some of the light is absorbed by the material and some is reflected. Most metals, wood and animals are made of opaque material.