Observations/Specular reflection
Specular reflection
Specular reflection, or regular reflection, is the mirror-like reflection of light from a surface.
Light reflects off surfaces in a very predictable manner - in accordance with the law of reflection. Once a normal to the surface at the point of incidence is drawn, the angle of incidence can then be determined. The light ray will then reflect in such a manner that the angle of incidence is equal to the angle of reflection. This predictability concerning the reflection of light is applicable to the reflection of light off of level (horizontal) surfaces, vertical surfaces, angled surfaces, and even curved surfaces. As long as the normal (perpendicular line to the surface) can be drawn at the point of incidence, the angle of incidence can be measured and the direction of the reflected ray can be determined. A series of incident rays and their corresponding reflected rays are depicted in the diagram below. Each ray strikes a surface with a different orientation; yet each ray reflects in accordance with the law of reflection.
Specular reflections vs diffuse reflection
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.
Specular reflections in photography
In photography, Many people have witnessed in person or have seen a photograph of a beautiful nature scene captured by a photographer who set up the shot with a calm body of water in the foreground. The water (if calm) provides for the specular reflection of light from the subject of the photograph. Light from the subject can reach the camera lens directly or it can take a longer path in which it reflects off the water before traveling to the lens. Since the light reflecting off the water undergoes specular reflection, the incident rays remain concentrated (instead of diffusing). The light is thus able to travel together to the lens of the camera and produce an image (an exact replica) of the subject which is strong enough to perceive in the photograph.
Reflections on curved surfaces
In the diagram, the ray of light approaching the mirror is known as the incident ray (labeled I in the diagram). The ray of light that leaves the mirror is known as the reflected ray (labeled R in the diagram). At the point of incidence where the ray strikes the mirror, a line can be drawn perpendicular to the surface of the mirror. This line is known as a normal line (labeled N in the diagram). The normal line divides the angle between the incident ray and the reflected ray into two equal angles. The angle between the incident ray and the normal is known as the angle of incidence. The angle between the reflected ray and the normal is known as the angle of reflection. (These two angles are labeled with the Greek letter "theta" accompanied by a subscript; read as "theta-i" for angle of incidence and "theta-r" for angle of reflection.) The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.
If water curved, the reflection would be distorted similar to what is seen in convex mirrors. Since light rays will reflect at the same angle as they hit the surface, but will shift based on the angle of the surface.
Other types of specular reflection
In addition to visible light, specular reflection can be observed in the reflection of radio waves and non-electromagnetic waves, such as with "acoustic mirrors" reflect sound.