Reflection

Reflection, phenomenon of light and other wave motions in which the light or other wave motion is returned after impinging on a surface, or the boundary between two media.

There are two laws of reflection:

• The incident ray, the reflected ray, and the normal (an imaginary line perpendicular to the reflecting surface at the point of incidence) all lie in the same plane.
• The angle of incidence equals the angle of reflection.

Using the two laws of reflection, the position at which the eye observes an image in a mirror can be established. Rays of light start from all points and directions. At the point where they strike a mirror, they are reflected, with the angle of reflection equal to the angle of incidence in each case. The eye observes the ray as it is reflected away from the normal. However, because the eye cannot identify the fact that the ray has been reflected on the way, it sees the ray as if it has travelled in a straight line starting from behind the mirror. In a plane mirror, the position of this observed image is perpendicularly opposite to the light source, along the normal, and an equal distance behind the mirror. It is a so-called virtual image, unlike the images produced by some lenses and curved mirrors, because there is, in reality, no light present at the point where the image is observed; the light only appears to be coming from there.

Reflection of light occurs from every surface that is visible to the eye, not only from mirrors. With most objects, which have rough surfaces, the light is reflected in all directions.This is called diffuse reflection. If white light falls on an object that appears red, the red light present in the original light is being diffusely reflected, while the other colours (other wavelengths) are being absorbed by the pigment of the red object.

For further discussion of the reflection of light, see Optics. For reflection of radio waves, see Ionosphere; Radio.

See also Electromagnetic Radiation; Sound; Telescope.