There is a law of reflection, which describes that a reflected ray of light usually emerges from the reflecting surface at the same angle as the incident ray falling on the mirror. But the incident ray and the reflecting ray are on opposing sides of the surface normal plane, which is the plane that forms from the incident ray and reflecting ray.
The concept of reflection was first introduced by Hero of Alexander in AD c. Regular reflection differs from diffuse reflection because, in diffuse reflection, the reflected rays tend to scatter away from the surface.
According to the law of reflection, the light that encounters a boundary is affected by the optical and electronic response functions of the material towards the electromagnetic radiation. During regular reflection, the light reflects and arrives at the same angle. We can experimentally show the difference between regular reflection and disuse reflection by coating a surface with glossy paint and matte paint; the matte paint mainly shows the specular reflection behavior, while the surface with glossy paint mainly shows diffuse reflection.
Some examples of regular reflection include visible light on a mirror, radio waves, and microwaves on flying objects, acoustic mirrors reflects sound and atomic mirrors reflect neutral atoms.
Diffuse reflection refers to the reflection of light or other waves from a surface through the scattering effect. Reflection off of smooth surfaces such as mirrors or a calm body of water leads to a type of reflection known as specular reflection. Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway leads to a type of reflection known as diffuse reflection. Whether the surface is microscopically rough or smooth has a tremendous impact upon the subsequent reflection of a beam of light.
The diagram below depicts two beams of light incident upon a rough and a smooth surface. A light beam can be thought of as a bundle of individual light rays which are traveling parallel to each other.
Each individual light ray of the bundle follows the law of reflection. If the bundle of light rays is incident upon a smooth surface, then the light rays reflect and remain concentrated in a bundle upon leaving the surface. On the other hand, if the surface is microscopically rough, the light rays will reflect and diffuse in many different directions.
For each type of reflection, each individual ray follows the law of reflection. However, the roughness of the material means that each individual ray meets a surface which has a different orientation. The normal line at the point of incidence is different for different rays. Subsequently, when the individual rays reflect off the rough surface according to the law of reflection, they scatter in different directions.
The result is that the rays of light are incident upon the surface in a concentrated bundle and are diffused upon reflection. The diagram below depicts this principle. The normal line approximated at each point of incidence is shown in black and labeled with an N. With this variation, normals at neighboring points are no longer parallel to each other. Since the angle of incidence depends on the normal line at the exact point a ray hits, the incident angles for a set of parallel rays will not be the same and each reflected ray will have a different angle of reflection.
In other words, the rays scatter. The orientation of the normal lines at neighboring points along a surface differentiates specular from diffuse reflection.
If the normal lines are parallel, reflection will be specular. If they are not parallel, reflection will be diffuse. Note, this is roughness at the microscopic level. Diffuse reflection occurs on surfaces that are smooth to the touch, such as paper.
Specular reflection occurs on curved surfaces such as a fun house mirror. Moving the slider to the left produces a progressive smoother surface. At the far left boundary of the Surface Roughness slider, the surface becomes totally flat and exhibits specular reflection of all incident wavelengths that match the color of the surface. Most things that we see people, cars, houses, animals, trees, etc.
For instance, an apple appears a shiny red color because it has a relatively smooth surface that reflects red light and absorbs other non-red such as green, blue, and yellow wavelengths of light. The reflection of light can be roughly categorized into two types of reflection: specular reflection is defined as light reflected from a smooth surface at a definite angle, and diffuse reflection , which is produced by rough surfaces that tend to reflect light in all directions as illustrated in Figure 1.
There are far more occurrences of diffuse reflection than specular reflection in our everyday environment. To visualize the differences between specular and diffuse reflection, consider two very different surfaces: a smooth mirror and a rough reddish surface. The mirror reflects all of the components of white light such as red, green, and blue wavelengths almost equally and the reflected specular light follows the same angle from the normal, as does the incident light.
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