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return of a wave from a surface that it strikes into the medium through which it has traveled. The general principles governing the reflection of light and sound are similar, for both normally travel in straight lines and both are wave phenomena. Objects are visible because of the light reflected from their surfaces, and their color depends on their ability to reflect light of a certain wavelength and to absorb that of other wavelengths. The reflection of sound waves from a surface is called an echoecho,
reflection of a sound wave back to its source in sufficient strength and with a sufficient time lag to be separately distinguished. If a sound wave returns within 1-10 sec, the human ear is incapable of distinguishing it from the orginal one.
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The Laws of Reflection

The reflection of light follows certain definite laws. A ray of light striking a reflecting surface at right angles to it is returned directly along the path it has followed in reaching the surface. When, however, a ray strikes a reflecting surface at any other angle, it is reflected at an angle in an opposite direction. The incoming ray is called the incident ray. Its direction is usually described by the angle of incidence, which is the angle that it makes with the normal, or line perpendicular to the reflecting surface at the point of reflection. The angle formed by the reflected ray and the normal is called the angle of reflection and is equal to the angle of incidence. Furthermore, the reflected ray is always in the same plane as the incident ray, and this plane is perpendicular to the surface.

The Degree and Types of Reflection

Not all surfaces reflect light in the same way or to the same degree. The measure of the fraction of light that is reflected by a material is called its reflectance. Metals in general have high values of reflectance; silver, for example, has a reflectance of about 96%. Smooth surfaces give regular reflection, also called specular reflection, in which incident parallel rays remain parallel after reflection. Rough or uneven surfaces give diffuse reflection, since the reflected rays are scattered and not parallel. For example, reflection by a mirrormirror,
in optics, a reflecting surface that forms an image of an object when light rays coming from that object fall upon it (see reflection). Usually mirrors are made of plate glass, one side of which is coated with metal or some special preparation to serve as a reflecting
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 is regular; by a highly polished but uneven piece of metal, it is diffused. Reflection of light is also brought about under certain conditions by the surfaces of transparent media through which light normally passes. An example is seen in the blazing glare of sunlight on a window or an automobile windshield when the sun's rays strike it at a very oblique angle.

A corner reflector returns a ray that is exactly parallel to the incident ray back to the incident ray's point of origin, or very close to it. The reflector is formed by intersecting three mutually perpendicular planes, with the centerpoint therefore being located at the mutual point of intersection. Such a device can be utilized as a radar target or marker for range finding and surveying. For increased visibility at night microscopic corner reflectors can be incorporated into reflective paint for road signs and incorporated into the lenses of bicycle and motorcycle reflectors. Several U.S. Apollo missions and one Soviet Lunakhod lunar probe deployed corner reflector arrays on the lunar surface. When the arrays are illuminated by laser beams originating from the earth, precise measurements of the roundtrip travel time of the light permit the calculation of the earth-moon distance to an accuracy of 6 in. (15 cm). Such measurements also are used to determine the moon's orbit with greater accuracy, to record perturbations in the moon's motion caused by meteorite impacts, and to ascertain the length of an earth day.

The phenomenon called total internal reflection is observed when light passing from one medium (e.g., a glass prism or water) to a less dense medium (e.g., air) reaches the boundary between the two media and is thrown back into the denser medium instead of passing outward as would be expected. This occurs when the light strikes at an oblique angle, greater than a certain degree. Up to that degree, refractionrefraction,
in physics, deflection of a wave on passing obliquely from one transparent medium into a second medium in which its speed is different, as the passage of a light ray from air into glass.
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 (not reflection) takes place, and the greatest angle at which refraction is possible is called the critical angle; if the angle of incidence exceeds this angle, total reflection occurs. The fire of a faceted diamond is due to total internal reflection. Internal reflection accounts in part for a number of natural phenomena. Rays of sunlight striking raindrops are refracted on entering them and then undergo internal reflection; since the sunlight is broken up into its colors, a rainbow appears. A miragemirage
, atmospheric optical illusion in which an observer sees in the distance a nonexistent body of water or an image, sometimes distorted, of some object or of a complete scene.
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 is also partially the result of internal reflection.


(ri-flek -shŏn) A phenomenon occurring when a beam of light or other wave motion strikes a surface separating two different media, such as air and glass or air and metal. Part of the wave has its direction changed, according to the laws of reflection, so that it does not enter the second medium. A rough surface will produce diffuse reflection. A smooth surface, as of polished metal, will reflect the radiation in a regular manner. The laws of reflection state firstly that the incident beam, the reflected beam, and the normal (the line perpendicular to the surface at the point of incidence) lie in the same plane, and secondly that the two beams are inclined at the same angle to but on either side of the normal.


The process by which incident light flux leaves a surface, or medium, from the incident side, without a change in frequency.



a universal property of matter, consisting in the reproduction of that which belongs to the object reflected. “It is logical to assert that all matter possesses a property which is essentially akin to sensation, the property of reflection” (V. I. Lenin, Poln. sobr. soch, 5th ed., vol. 18, p. 91). Any reflection carries information about the object of reflection. Both the capacity for reflection and the nature of its manifestation depend on the level of organization of matter. Reflection appears in qualitatively different forms in inorganic nature, in the world of plants and animals, and, finally, among human beings. The interaction of different material systems results in mutual reflection in the form of simple mechanical deformation (such as the imprint of a body in sand), contraction or expansion depending on temperature changes (for example, a thermometer), reflection of light, changes in electromagnetic waves (such as photography), the reflection of sound waves (an echo), chemical changes (for instance, the color of litmus paper), and physiological processes (for example, contraction of the pupil of the eye in bright light). The invention of electronic computers capable of recognizing patterns, distinguishing objects, carrying out operations of formal logic, and developing conditioned reflexes—in short, capable of reflecting the relationships among things and orienting themselves in the world—reaffirms the idea of reflection as a universal property of matter.

An essential property of living organisms is irritability—the reflection of the influences of the external and internal environment in the form of excitation and selective response. Irritability is a prepsychological form of reflection, a means of regulating adaptive behavior. A later stage in the development of reflection is associated with the appearance, in higher living organisms, of sensitivity—that is, the ability to experience sensations, which are the primary form of animal psychology. The development of sense organs and the coordination of their functioning led to perception, the ability to reflect things as the totality of their properties. Animals not only differentiate in their perception of the properties and relationships of things, but they also reflect a considerable number of biologically important relationships in the environment. This is an elementary form of thinking, which reaches its highest level in anthropoid apes and dolphins.

The development of man and human society through work and communication with the aid of speech resulted in the appearance of a specifically human, essentially social, form of reflection: consciousness and self-consciousness. Man’s reflection of reality differs from animal reflection in both the method and object of reflection; man strives not only to satisfy his basic needs but to understand the objective relations between things. The characteristic feature of human reflection is that it is somewhat ideal. It presupposes not only an influence on the subject from without, but also the subject’s independent actions and creative activity, manifested in his selective and purposeful perception, in his ability to abstract himself from some objects, properties, and relations and to focus on others, in the conversion of sensory images to logical thought, and in the use of conceptual forms of knowledge. The creative activity of man is also revealed in acts of productive imagination, in activity aimed at discovering truth through the formulation and testing of a hypothesis, in the development of a theory, and in the formulation of new ideas, plans, and aims.

V. I. Lenin made an important contribution to the theory of cognition as a reflection of reality. Therefore, the dialectical-materialist theory of reflection is correctly called the Leninist theory of reflection. The Leninist principle of reflection has been attacked by certain revisionists and bourgeois ideologists, notably H. Lefebvre, R. Garaudy, and G. Petrović, who assert that the theory of reflection restricts man to “that which exists” (since it is impossible to reflect the future—that which does not yet exist) and underestimates the creative activity of consciousness. They advocate replacing the category of reflection with the concept of practice. The groundlessness of this criticism, which replaces the dialectical-materialist concept of reflection with a mechanistic interpretation of it, is self-evident. Lenin never denied the creative activity of consciousness: “man’s consciousness not only reflects the objective world, but creates it” (ibid., vol. 29, p. 194). But the creative activity of man, who transforms the world, is only possible through an adequate reflection of the objective world.

The principle of reflection is the cornerstone of the materialist theory of knowledge, which rests on a recognition of the primacy of the external world and the re-creation of it in human consciousness. Lenin noted that the concept of reflection was part of the definition of dialectical, consistent materialism, and from this standpoint he criticized the epistemology of subjective and objective idealism.


Lenin, V. I. “Materializm i empiriokrititsizm.” Poln. sobr. soch, 5th ed., vol. 18.
Lenin, V. I. “Filosofskie tetradi.” Poln. sobr. soch, vol. 29.
Pavlov, T. Teoriia otrazheniia. Moscow, 1949.
Rubinshtein, S. L. Bytie i soznanie. Moscow, 1957.
Korshunov, A. M. Teoriia otrazheniia i sovremennaia nauka. Moscow, 1968.
Ukraintsev, B. S. Otrazhenie ν nezhivoi prirode. Moscow, 1968.
Problemy otrazheniia. Moscow, 1969.
živković, L. Teoriia sotsial’nogo otrazheniia. Moscow, 1969. (Translated from Serbo-Croatian.)
Leninskaia teoriia otrazheniia i sovremennost’. Sofia, 1969.
Tiukhtin, V. S. Otrazhenie, sistemy, kibernetika. Moscow, 1972.




a form of speculation directed at understanding one’s own actions and the laws that govern them; self-knowledge revealing the specifics of man’s inner world. The content of reflection is determined by sensuous, objective activity; ultimately, reflection is the awareness of practice (seePRACTICE) and the objective world of culture. In this sense, reflection is a method of philosophy and dialectic is the reflection of reason.


The reflection of a configuration in a line, in a plane, or in the origin of a coordinate system is the replacement of each point in the configuration by a point that is symmetric to the given point with respect to the line, plane, or origin.
Two permutations, a and b, of the same objects are reflections of each other if the first object in a is the last object in b, the second object in a is the next-to-last object in b, and so forth, with the last object in a being the first object in b.
The return of waves or particles from surfaces on which they are incident.


The change of direction which a ray of light, sound, or radiant heat undergoes when it strikes a surface; also see law of reflection.


(less commonly), reflexion
1. Maths a transformation in which the direction of one axis is reversed or which changes the sign of one of the variables
2. Anatomy the bending back of a structure or part upon itself


(1) A characteristic of light (see reflective).

(2) A feature of some programming languages and scripting languages that allows them to change their own structure at runtime. It typically refers to interpreted languages that can, for example, accept source code as input, which modifies the program's original behavior when executed. A compiler may also provide meta-data that can be used for reflection at runtime. See also reflection mapping.

(3) (Reflection) A family of connectivity software from Attachmate Corporation that runs under Windows. Reflection products include terminal emulation for Unix, HP, OpenVMS, IBM and X Window as well as NFS support for clients and NT servers. The Reflection line was originally the flagship product offering of WRQ, Inc., which Attachmate acquired in 2005.
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