Basic understanding of the reflection and refraction properties of light paved the way for many of the optical measuring devices in use today. When light strikes a surface, a portion of the incident ray is reflected from the surface. Depending on the surface characteristics, either specular reflection or diffuse reflection is observed. When light passes through an optically dense media, such as glass or water, the incident light ray bends as it enters the media. The characteristics of the material (air, glass, water, etc.) and the orientation of the ray determine the path of a reflected or refracted ray.