Modern physical optics considers light as a kind of electromagnetic waves perceived by the human eye. In other words, we can say that light is visible electromagnetic radiation.

visible light

As you know, electromagnetic waves differ in frequency and wavelength. And depending on these values, electromagnetic radiation is divided into frequency ranges.

Outside of physical optics, the concept of "light" also includes electromagnetic waves, not visible to the eye human, in the infrared range with a wavelength of 1 mm - 780 nm and a frequency of 300 GHz - 429 THz and in the ultraviolet range with a wavelength of 380 - 10 nm and a frequency of 7.5 10 14 Hz - 3 10 16 Hz.

Infrared, visible and ultraviolet radiation are called optical region of the spectrum. The upper limit of the optical range is the long-wave limit of infrared radiation, and the lower limit is the short-wave limit of ultraviolet radiation. Thus, the range of optical radiation is from 1 mm to 10 nm.

How does light come about? It turns out that it is formed as a result of processes occurring inside atoms when their state changes. This creates a stream of particles called photons. They have no mass, but they have energy.

It turns out that light simultaneously has the properties of an electromagnetic wave and the properties of discrete particles - photons.

Sources of light

Any body that emits electromagnetic waves with a frequency located in the range visible light, can be called a light source. All light sources are divided into natural, created by nature itself, and artificial, created by people.

The most important natural source of light on Earth is, of course, the Sun. It gives us not only light, but also warmth. Thanks to the energy of sunlight, life exists on our planet. Light is emitted by the Moon, stars, comets and other cosmic bodies. Sources of natural light can be not only bodies, but also natural phenomena. During a thunderstorm, we see how powerful light illuminates everything around a flash of lightning. Polar lights, luminous living organisms, minerals, etc. - this is also natural springs Sveta.

The very first and most ancient artificial source of light can be called the fire of a fire. Later, people learned to use other types of fuel and create portable light sources: candles, torches, oil lamps, gas lanterns, etc. All these sources were based on combustion and, together with light, emitted a large amount of heat.

With the invention of electricity, electric light bulbs appeared, which are still used by people as light sources.

geometric optics

The propagation of light in a transparent medium, its reflection from mirror-reflecting surfaces, refraction at the boundary of two transparent media occurs according to certain laws, the study of which is engaged in geometric optics.

To study various light phenomena in geometric optics, concepts such as a point source of light and a light beam are used.

The basic concept of geometric optics is light beam .

An ordinary lamp spreads light evenly in all directions. Let us cover this lamp with an opaque material in such a way that the light emitted by it can only pass through a small narrow hole. A narrow light flux will go through it, directed along a straight line. This line along which the light beam propagates is called the light beam. The direction of this beam does not depend on its transverse dimensions.

Candles, lanterns, lamps and other light sources are quite big sizes compared to the distance over which their light travels. They are called extended light sources . Point light source a source is considered to be the size of which can be neglected in comparison with the distance to which this light reaches. For example, a cosmic star, which is actually huge, can be considered a point source of light, since the distance over which this light propagates is huge compared to the size of the star itself.

Consider the basic laws of geometric optics.

The law of rectilinear propagation of light

In a transparent homogeneous medium, light propagates in a straight line. The proof of this law is an experiment in which light from a point source passes through a small hole in the screen. As a result, a narrow light beam is formed, and in a plane located behind the screen parallel to it, a regular light circle appears centered on the straight line along which the light propagates.

Place a small object between the light source and the screen. On the screen we will see the shadow of this object. Shadow is the area where the light beam does not reach. Its appearance is explained by the rectilinear propagation of light. If the light source is a point, then only a shadow is formed. If its dimensions are quite large compared to the distance to the object, then a shadow and penumbra are created. After all, in this case, light rays come from each point of the source. Some of them, falling into the shadow area, highlight its edges, and thereby create penumbra - the area in which the light rays fall partially.

The law of rectilinear propagation explains the nature of the solar and lunar eclipse. Solar eclipse occurs when the moon is between the sun and the earth, and the shadow of the moon falls on the earth.

The law of rectilinear propagation of light was used by the ancient Greeks when installing columns. If the columns are placed strictly in a straight line, then the closest of them will visually cover all the others.

Law of light reflection

If a reflective surface is encountered in the path of the light beam, then the light beam changes its direction. The incident and reflected rays and the normal (perpendicular) to the reflecting surface, reconstructed at the point of incidence, lie in the same plane. The angle between the rays is divided by this normal into two equal parts. The most common formulation of the law of reflection is: The angle of incidence is equal to the angle of reflection". But this definition does not indicate the direction of the reflected beam. Meanwhile, the reflected beam will go in the opposite direction to the incident beam.

If the dimensions of the surface irregularities are less than the wavelength of light, then the rays incident in a parallel stream will be reflected specularly and will also go in parallel streams.

If the dimensions of the irregularities exceed the wavelength, then the narrow beam will be scattered, and the reflected rays will go in different directions. This reflection is called diffuse, or scattered. But, despite the random scattering, the law of reflection is also fulfilled in this case. For any ray, the angle of incidence and the angle of reflection will be equal.

Law of refraction of light

Dip the pencil in a cup of water. Visually, it seems to us that he seemed to have broken in two on the surface of the water. In fact, nothing happened to the pencil. The reason is that a beam of light falls on the surface of the water at one angle, and goes deeper into the water at another. Because of this, the size and location of physical bodies are distorted.

Changing the direction of a light beam at the interface between two media transparent to light waves called refraction Sveta.

The law that describes the refraction of light waves is called Snell's law(Snell or Snell) named after its author, the Dutch mathematician Willebrord Snell, who discovered it in 1621.

According to this law, the angle of incidence of light on the interface and the angle of refraction are related by the relation:

n 1 sinƟ 1 = n 2 sinƟ 2 ,

or sin Ɵ 1 / sin Ɵ 2 = n 2 / n 1 ,

where n 1 is the refractive index of the medium from which light is incident on the interface;

Ɵ 1 is the angle between the light beam incident on the interface and the normal to this surface;

n 2 - the refractive index of the medium into which light enters after the interface;

Ɵ 2 is the angle between the beam passing through the interface and the normal to this surface.

Refractive index of medium is the ratio of the speed of light in vacuum to its speed in a given medium:

n = c/v

The more it differs from unity, the greater will be the angle of deflection of the light beam during the transition from vacuum to medium.

Attitude n 2 / n 1 called relative refractive index .

A light beam entering a denser medium forms a smaller angle with the normal to this surface, that is, it is refracted downward. But in reality it seems that this angle, on the contrary, is larger than the angle of incidence. As a result of this, we observe a distortion in the size, shape and location of objects. Objects in the water seem to us larger than they really are, and located higher. So, bathers are often mistaken when estimating the depth of the reservoir. They see the bottom elevated, and the depth seems less to them.

Due to the refraction of sunlight in the atmosphere, we observe the sunrise a little earlier and the sunset a little later than these phenomena would occur if there were no atmosphere.

Based on the phenomenon of refraction, the lenses of photo and movie cameras, microscopes, telescopes, binoculars and other optical instruments, which include optical lenses or prisms, are built.

When light passes from a denser medium to a less dense one (for example, from water to air), one can observe total internal reflection of a light beam . It occurs when the angle of incidence is equal to a certain value called limiting angle total internal reflection . In this case, the incident rays are completely reflected from the interface. The refracted rays disappear completely.

This phenomenon is used in fiber LEDs, which are made from an optically transparent material. They are very thin threads. The light entering them is completely reflected from the inner side surfaces and spreads over long distances.

Geometric optics considers the properties of light without taking into account its wave theory and quantum phenomena. Of course, it cannot accurately describe optical phenomena. But since its laws are much simpler than generalizing wave laws, it is widely used in the calculation of optical systems.

Visible radiation- electromagnetic waves perceived by the human eye, which occupy a portion of the spectrum with a wavelength of approximately 380 (violet) to 740 nm (red). Such waves occupy the frequency range from 400 to 790 terahertz. Electromagnetic radiation with these wavelengths is also called visible light , or simply light(in the narrow sense of the word). The human eye is most sensitive to light at 555 nm (540 THz), in the green part of the spectrum.

Visible radiation also enters the "optical window", a region of the spectrum of electromagnetic radiation that is practically not absorbed by the earth's atmosphere. Clean air scatters blue light a little more than longer wavelengths (toward the red end of the spectrum), so the midday sky looks blue.

Many species of animals are able to see radiation that is not visible to the human eye, that is, not included in the visible range. For example, bees and many other insects see light in the ultraviolet range, which helps them find nectar on flowers. Plants pollinated by insects are in a better position in terms of procreation if they are bright in the ultraviolet spectrum. Birds are also able to see ultraviolet light (300-400 nm), and some species even have markings on their plumage to attract a partner, visible only in ultraviolet light.

Visible spectrum

When a white beam is decomposed in a prism, a spectrum is formed in which radiation of different wavelengths is refracted at different angles. The colors included in the spectrum, that is, those colors that can be obtained by light waves of one wavelength (or a very narrow range), are called spectral colors. The main spectral colors (having their own name), as well as the emission characteristics of these colors, are presented in the table:

Visible radiation - electromagnetic waves perceived by the human eye, which occupy a region of the spectrum with wavelengths from approximately 380 (violet) to 780 nm (red). Such waves occupy the frequency range from 400 to 790 terahertz. Electromagnetic radiation with such wavelengths is also called visible light, or simply light (in the narrow sense of the word). The human eye is most sensitive to light at 555 nm (540 THz), in the green part of the spectrum.

Visible radiation also enters the "optical window", a region of the spectrum of electromagnetic radiation that is practically not absorbed by the earth's atmosphere. Clean air scatters blue light a little more than longer wavelengths (toward the red end of the spectrum), so the midday sky looks blue.

Many species of animals are able to see radiation that is not visible to the human eye, that is, not included in the visible range. For example, bees and many other insects see light in the ultraviolet range, which helps them find nectar on flowers. Plants pollinated by insects are in a better position in terms of procreation if they are bright in the ultraviolet spectrum. Birds are also able to see ultraviolet light (300-400 nm), and some species even have markings on their plumage to attract a partner, visible only in ultraviolet light.

The first explanations of the spectrum of visible radiation were given by Isaac Newton in the book "Optics" and Johann Goethe in the work "Theory of Colors", but even before them, Roger Bacon observed the optical spectrum in a glass of water. Only four centuries after this, Newton discovered the dispersion of light in prisms.

Newton first used the word spectrum (lat. spectrum - vision, appearance) in print in 1671, describing his optical experiments. He made the observation that when a beam of light hits the surface of a glass prism at an angle to the surface, some of the light is reflected and some passes through the glass, forming bands of different colors. The scientist suggested that light consists of a stream of particles (corpuscles) of different colors, and that particles of different colors move at different speeds in a transparent medium. According to his assumption, red light traveled faster than violet, and therefore the red beam was not deflected on the prism as much as violet. Because of this, a visible spectrum of colors arose.

Newton divided light into seven colors: red, orange, yellow, green, blue, indigo, and violet. The number seven he chose from the belief (derived from the ancient Greek sophists) that there is a connection between colors, musical notes, objects solar system and days of the week. The human eye is relatively weakly sensitive to indigo frequencies, so some people cannot distinguish it from blue or violet. Therefore, after Newton, it was often proposed to consider indigo not an independent color, but only a shade of violet or blue (however, it is still included in the spectrum in the Western tradition). In the Russian tradition, indigo corresponds to blue.

Goethe, unlike Newton, believed that the spectrum arises when different components of light are superimposed. Observing wide beams of light, he found that when passing through a prism, red-yellow and blue edges appear at the edges of the beam, between which the light remains white, and the spectrum appears if these edges are brought close enough to each other.

In the 19th century, after the discovery of ultraviolet and infrared radiation, the understanding of the visible spectrum became more accurate.

In the early 19th century, Thomas Jung and Hermann von Helmholtz also explored the relationship between the visible spectrum and color vision. Their theory of color vision correctly assumed that it uses three different kinds of receptors to detect eye color.

Characteristics of the boundaries of visible radiation

When a white beam is decomposed in a prism, a spectrum is formed in which radiation of different wavelengths is refracted at different angles. The colors included in the spectrum, that is, those colors that can be obtained by light waves of one wavelength (or a very narrow range), are called spectral colors. The main spectral colors (having their own name), as well as the emission characteristics of these colors, are presented in the table:

Visible radiation is a spectrum of electromagnetic oscillations of a long wave from 400 to 750 nm, consisting of seven colors (orange, red, yellow, blue, blue, violet, green). This type irradiation is able to cause physico-chemical reactions in the body that are close in energy parameters to , and is used together with it. The use of visible radiation for therapeutic and prophylactic purposes is called chromotherapy.

Action on the body

Visible radiation quanta have a high frequency and high energy. This gives them the opportunity to transfer atoms to an excited state and increase their ability to biochemical interactions. The biological effect of radiation depends on the depth of its penetration into the tissues. It penetrates the skin to a depth of one centimeter and is absorbed by the surface of the skin. In this case, heat is released, which changes local metabolic processes and causes segmental reactions. As a result, microcirculation and tissue nutrition are improved, immunogenesis and the release of biologically active substances into the blood are activated. Important influence the method affects a person through the retina of the eye, as it is perceived through the organ of vision, having a reflex and indirect effect on the central nervous system, and as a result, on the mental processes in the body.

color treatment

The color effect on a person is multifaceted. It is believed that orange, yellow and red are active colors, while blue and violet are passive. It has been established that active colors are tiring, while green and blue are invigorating. At the same time, orange and red have an exciting effect on the body, blue - inhibitory, and green and yellow balance these processes. There is an opinion that Orange color stimulates the kidneys, yellow color normalizes arterial pressure and the functioning of the digestive system. Green color normalizes the work of the heart, and purple and blue - the functioning of the brain. Blue spectrum radiation promotes the breakdown of hematoporphyrins and is used to treat neonatal jaundice. Significant effect on the human body White color. It is with its lack in winter that depressive disorders can develop due to a reduction in daylight hours.

Therapeutic effects of visible radiation

1. Improvement of blood supply and tissue trophism.
2. Stabilization of functioning of irradiated organs.
3. metabolic effect.
4. Photodestruction.
5. Normalization of functioning nervous system and psycho-emotional state of the patient.

Indications for use

1. Diseases of the peripheral nervous system (neuritis, radicular syndrome).
2. and muscles.
3. Consequences of traumatic damage to the joints, ligamentous apparatus.
4. Pathological processes of internal organs of an inflammatory nature.
5. Contractures, infiltrates.
6. Long-term healing wounds.
7. Frostbite.

Chromotherapy using red and blue is used in dermatology for the treatment of acne.

Contraindications

1. Photophthalmia (acute eye damage due to radiation).
2. Acute purulent inflammatory processes.
3. Bleeding.
4. Blood diseases.
5. Circulatory failure.
6. Active .
7. Malignant neoplasms.

Methodology

The impact is carried out on naked parts of the human body. The light source can be solar lamps, medical reflectors, LED emitters. The distance from the reflector to the surface of the irradiation area is determined by the type and power of these sources. If the impact is carried out on the skin, then the patient's eyes should be protected with special glasses. Dosing of the procedure is carried out according to the subjective sensations of the patient and according to the energy flux density. Methods of psychophysiological assessment of color perception can be used. The duration of the procedures and their number is selected individually. The treatment session lasts about 20 minutes and is accompanied by a feeling of light warmth. The course of treatment accounts for 10 to 20 procedures that are performed every day. If necessary, repeated courses of phototherapy are prescribed after 4-5-6 weeks.

Conclusion

The therapeutic effect of visible radiation has found wide application in medicine. Chromotherapy is a safe and affordable method of treating various diseases, which has practically no side effects and complications. This method of physiotherapy can be successfully combined with other medical procedures. As a result of taking a course of phototherapy, patients feel better, their psycho-emotional state improves.

Cosmetologist Yulia Orishchenko talks about chromotherapy:

TV channel "Russia-1", the program "Morning of Russia", a story about chromotherapy:

- Listen, why are there seven colors in the rainbow?
Because there are seven notes.
Why is an orange orange?
- It should be so, it's blue ...

(From conversations at the Faculty of Physics)

Last year, I received a letter from a Moscow teacher, in which she was interested in why there are 7 colors in the rainbow. This question is not as simple as it might seem, and at one time was difficult even for Newton. As you know, he initially singled out 5 primary colors of the spectrum (red, yellow, green, blue and violet), to which he later added orange and indigo.

Representatives different peoples in their languages, they distinguish a different number of colors of the rainbow, which, moreover, changes over time. For example, in 1703, the people of Kiev pointed to 4 colors of the rainbow: “In the rainbow, the properties are scarlet, and blue, and green, and crimson” ( Kolesov V.V. The history of the Russian language in stories. - M., Prosv., 1982).

In natural languages, absolute and relative colors are distinguished. Absolute colors - black, white, red, etc., relative - carrot, dark red. The number of absolute colors in the languages ​​of different peoples of the world is rarely more than three dozen, but there are languages ​​where their number is very small: in one of the African tribes 2 (dark and light), in the Maidu language of the North American Indians of Northern California - 3 (blue-green, red, yellow-orange-brown), in Japan - 4 (white, black, red, blue-green), in China - 5 (white, black, red, blue-green, yellow). By the way, in Europe 3 "primary" colors were fixed (at first - red, yellow, blue, and later - red, green and blue), and since the time of Newton they often talk about 7 colors. But even in this case, the colors are not necessarily the same. In the Kazakh language, for example, the rainbow has seven colors, but the colors are not the same. The color that is translated into Russian as blue in Kazakh perception is a mixture of blue and green, yellow is a mixture of yellow and green. That is, what is considered a mixture of colors by Russians is considered an independent color by Kazakhs. American orange is by no means our orange, but rather red in our understanding. (By the way, in the case of hair color, on the contrary, red is red.)

Of course, in fact, almost colors are represented in the rainbow (except, for example, white, black and intermediate grays), and you can select as many primary colors as you want. Why did Newton stop at seven? Most likely, because to Newton, seven seemed an unusual number. To make the world seem more harmonious, so that the number of colors corresponds to the number of basic tones in the scale. In general, depending on the importance of certain colors and shades in the everyday life of the people, some of them may be more or less reflected in the language. In cultures for which it is vital to control and evaluate the condition of the grown plants, there are many words for expressing shades of green, for northern peoples for white, for southern peoples for yellow. (For the sake of completeness, let's point out that there are colors that are not in the rainbow at all. For example, purple or brown. These colors are a mixture of waves of different wavelengths, and no part of the rainbow corresponds to them.)

And to be completely honest, then in nature there are no flowers at all - only our imagination creates the illusion of color. The wavelengths of visible light (in the range of 380-740 nanometers) can be called any color - they will never know about it. But first, more about the light.

Light is electromagnetic radiation perceived by the human eye. In a broader sense, this concept also includes ultraviolet and infrared radiation invisible to the human eye. The corresponding wavelengths vary from 10 nanometers to 0.2 millimeters (see figure). Waves of different frequencies propagate differently. For example, human body opaque to the visible part of the spectrum, but does not present an obstacle to x-rays; infrared rays with a length of more than 1 micron cannot pass through a layer of water several centimeters thick, so water is used as a heat-shielding filter.

The words "electromagnetic radiation" mean a lot, but to the uninitiated reader they mean nothing. A brief evolution of understanding the nature of light is as follows: at the end of the 17th century, Isaac Newton proposed a corpuscular, and Christian Huygens - wave theory Sveta. According to the corpuscular theory, light was a stream of particles (corpuscles) emitted by luminous bodies, and the movement of light corpuscles obeyed the laws of mechanics. For example, the reflection of light was understood similarly to the reflection of an elastic ball from a plane, and the refraction of light was explained by a change in the speed of corpuscles when passing from one medium to another. The wave theory considered light as a wave process similar to mechanical waves. The theory was based on the Huygens principle, according to which each point that a wave reaches becomes the center of secondary waves, and the envelope of these waves gives the position of the wave front at the next moment in time.

As it turned out later, both approaches satisfactorily explained some phenomena, but were completely unsuitable for others. In the 60s of the 19th century, Maxwell established general laws electromagnetic field, which led him to the conclusion that light is not mechanical, but electromagnetic waves. electromagnetic theory light allowed to explain many phenomena, such as interference, diffraction, polarization, pressure of light. But to understand the phenomena of black body radiation, the photoelectric effect, the Compton effect, it was necessary to introduce quantum concepts, and in 1905 Albert Einstein, applying the quantum hypothesis of Max Planck to explain the phenomenon of the photoelectric effect, suggested that an electromagnetic wave consists of separate portions - light quanta, later called photons.

Thus, light is conceived by us as a form of matter (quantum field), which is neither waves nor a stream of particles, but exhibits their properties under certain conditions. This duality is called the wave-particle duality of light. To describe such objects, quantum mechanics arose, in which the state of a particle is described by a wave function.

Spreading, the light falls, in particular, on the retina - the inner shell of the eye, containing light-sensitive receptors. Perceiving electromagnetic radiation, photoreceptors convert it into electrical impulses and transmit it as a signal to the brain. The human retina contains 110-125 million rods, which are very sensitive to light and provide night vision, and 6-7 million cones responsible for color perception.

According to sensitivity to different wavelengths of light, there are three types of cones. S-type cones (short - short) are most sensitive in the violet-blue, short-wavelength part of the spectrum, M-type (medium - medium) - in green-yellow and L-type (long - long) - in the yellow-red, long-wavelength part spectrum. The presence of these three types of cones and rods, sensitive in the emerald green part of the spectrum, gives a person color vision. This is the “three-component theory of color vision” or “trichromatic theory of color perception” formulated in the 19th century (Thomas Jung, Hermann Helmholtz, James Clerk Maxwell).

The zones of sensitivity of medium-wavelength and long-wavelength cones overlap significantly, so cones of a certain type react not only to their color; they just react to it more intensely than others.

At night, when the flow of photons is insufficient for the normal operation of the cones, only the rods provide vision, so at night a person cannot distinguish colors. The sensitivity of a rod is sufficient to register the hit of a single photon, the sensitivity of cones is 100 times less: from several tens to several hundreds of photons must be hit. The sticks perceive light mainly in the emerald green part of the spectrum, so at dusk the emerald color seems brighter than all the others.

Rods react to light more slowly than cones - the rod reacts to a stimulus within about a hundred milliseconds. This allows you to be more sensitive to smaller amounts of light, but reduces your ability to perceive fast changes, such as fast image changes. When the brightness necessary for the perception of color is reached, the highly sensitive receptors of twilight vision - rods - are automatically turned off. The rods are predominantly located at the edges of the retina and are responsible for peripheral vision.

Cones perceive fast movements much better. The light sensitivity of cones is not high, therefore, sufficient illumination or brightness is necessary for good color perception. The most rich in color receptors are the central parts of the retina.

Now we can return to the concept of color. Color is a qualitative subjective characteristic of electromagnetic radiation in the visible range, determined on the basis of the resulting physiological visual sensation and depending on a number of physical, physiological and psychological factors. Color perception is also determined by its spectral composition, color and brightness contrast with surrounding light sources and non-luminous objects. Understanding this fact is very important for designers: yellow on a red background will appear greenish-yellow, and blue will take on a greenish tint.

AT human mind color has constancy - a fixed idea of ​​the color of an object as an integral feature of a familiar object of observation. In particular, the foliage of trees is unconsciously recognized as green even under reddish lighting at sunset. To introduce such a correction in an unfamiliar situation, surfaces with a white color are used: comparison with them as a "standard", along with the adaptation of the eye, allows you to unconsciously introduce a correction for lighting. For example, we enter a dark room and see a black ball on a gray rag, we realize that the gray rag is actually a white tablecloth, and we conjecture that the black ball is a red apple. In the absence of observational experience, color sensations and judgments of a person about the color of objects become uncertain or erroneous. So, descriptions and attempts to reproduce the color of "cosmic dawns" (sunrises and sunsets on Earth, observed from aboard a spacecraft), made by different astronauts, differ greatly from one another and from the color of these "dawns" recorded in photographs.

Over the years, the color vision of the world changes. This is due to the gradual clouding of the lens over the course of life, which is why the colors become more yellow. They tell the story of Ilya Repin, who at the end of his life was asked to restore his own painting, painted many years earlier. What was the surprise of the restorers when they saw that the artist did not match the color - now he saw differently.

Moreover, there are absolutely no ways to check whether we see the same colors. Indeed, when we were little, we asked adults what this or that color was called. And we learned to name the colors we see as we were told. At the same time, we could see the colors that we pointed at in a completely different way than these adults.

To understand color perception, you need to know about such a property of our vision as metamerism. Not all colors of the rainbow are "independent" of each other. Some of them can be obtained by mixing others. For example, if red and green rays hit the retina at the same time, then we will see one beam, and the yellow color and the eye will not notice the substitution (the experiment can be done using two projectors, crossing on a white screen the rays passed through one or another colored glass) . This phenomenon is called metamerism.

Metamerism is a property of vision in which light of different spectral composition can cause the sensation of the same color. The metamerism of a color increases with a decrease in its saturation, i.e. the less saturated the color, the a large number combinations of mixtures of radiations of different spectral composition, it can be obtained. White flowers are characterized by the greatest metamerism. Physiologically, the metamerism of vision is based on the structure of the peripheral part of the visual analyzer. Human vision is a three-stimulus analyzer. If the compared fluxes of radiation with different spectral composition produce the same effect on the cones, then the colors are perceived as the same.

The mathematical description of color marked the beginning of a new science - colorimetry. In 1853, Hermann Grassmann formulated three laws of color synthesis: the laws of "three-dimensionality", "continuity" and "additivity". "The law of three-dimensionality" - any color is uniquely represented as a combination of three independent colors (independence lies in the fact that none of these three colors can be obtained by adding the other two). "The law of continuity" - with a continuous change in radiation, the color also changes continuously; therefore, to any color you can pick up infinitely close. "The law of additivity" - the color of the mixture of radiations depends only on their colors, but not on the spectral composition; that is, the color of a mixture, for example, of yellow and violet, does not depend on the mixture of which colors, in turn, these yellow and violet colors were obtained.

Color vision is characteristic of many animal species. In vertebrates (monkeys, many species of fish, amphibians), and among insects in bees and bumblebees, color vision is trichromatic, like in humans. In ground squirrels and many species of insects, color vision is dichromatic, that is, it is based on the work of two types of light detectors, in birds and reptiles, vision is four-component. For insects, the visible region of the spectrum is shifted towards short-wave radiation and includes the ultraviolet range. Therefore, the world of insect colors is significantly different from ours.

In the animal world, four- and even five-stimulus color analyzers are known, so that colors perceived by humans as the same may appear different to animals (for example, birds of prey see traces of rodents on paths to burrows solely due to the ultraviolet luminescence of their urine components).

A similar situation develops with image registration systems, both digital and analog. Although for the most part they, like human vision, are three-stimulus (three layers of film emulsion, three types of cells of a digital camera or scanner matrix), their metamerism is different from that of human vision. Therefore, colors perceived by the eye as the same may appear different in a photograph.

Thus, the possibility was substantiated (up to the influence of lighting conditions and the subjectivity of color perception by an individual) to develop methods for quantitatively expressing color in the form of a set of three numbers. In 1860, Maxwell proposed to use red, green, blue as a trio of independent colors. The corresponding additive system by the first letters of the corresponding English words called RGB, and it currently dominates the color reproduction systems for monitors and televisions.

However, our eye perceives not only emitted, but also (mostly) reflected light. The question of the color of reflected light differs from that already considered. Recall the usual watercolor paints on a sheet of paper. A mixture of red and green dye does not produce yellow. The same is true in the limiting case: if you mix all the colors of the palette, you get not white, but dirty. What is the difference?

To understand the color perception of the reflected color, we must note that when radiation hits a certain surface, part of it can be partially or completely absorbed, while the other part is reflected. Joint action electromagnetic radiation in the entire visible part of the spectrum causes a sensation of white light, and the separate action of the totality of radiations remaining after the absorption of some of them - colored.

At the same time, we see the reflected, that is, not absorbed, part of the spectrum that has fallen into our eye. Therefore, the dye, perceived by us as orange, in fact, absorbed all the rays, except for giving the sensation of orange. And this means that the reflected surface is actually greenish-blue. (And if we could make the surface of an orange glow, we would see it for ourselves.) In this sense, the oranges we love are actually the color of eggplants, and eggplants, on the contrary, are painted in cheerful orange tones (see table).

To describe the reflected color in 1951, Andy Muller proposed a subtractive (subtractive) CMYK model (from the English words cyan, magenta, yellow, key). This system has advantages in printing, color photography and printing. For example, a computer supplies emitted colors to a monitor in the RGB system, and to printers in the CMYK system.

Understanding light as an electromagnetic wave is close to understanding sound as a mechanical wave. The main property of all waves, regardless of their nature, is that in the form of a wave, energy is transferred without transfer of matter (the latter can take place only as a side effect). For example, after a wave generated by a stone thrown into water passes over the surface of a liquid, the particles of the liquid will remain approximately in the same position as before the wave passed.

Sound is vibrations of an elastic medium propagating in the form of waves in a gaseous, liquid or solid medium. In a narrow sense, this is a phenomenon subjectively perceived by the ear of humans and animals.

A person hears sound with a frequency of 16 Hz to 20,000 Hz. physical concept about sound covers both audible and inaudible sounds. Sound with a frequency below 16 Hz is called infrasound, above 20,000 Hz - ultrasound. High-frequency elastic waves in the range from 10 9 to 10 12 -10 13 Hz are referred to as hypersound.

The range of infrasonic frequencies from below is practically unlimited - in nature, infrasonic vibrations occur with a frequency of tenths and hundredths of a hertz. The frequency range of hypersonic waves is limited from above by physical factors that characterize the atomic and molecular structure of the medium: the length of the elastic wave must be much greater than the mean free path of molecules in gases and greater than the interatomic distances in liquids and in solids. Therefore, hypersound with a frequency of 109 Hz and higher cannot propagate in the air, and with a frequency of more than 10 12 -10 13 Hz in solids.

The main parameters of any waves, including sound waves, are the frequency and amplitude of oscillations. The frequency of sound is measured in hertz (Hz - the number of vibrations per second). The human ear is capable of perceiving sound from approximately 16 Hz to 20 kHz.

The amplitude of sound vibrations is called sound pressure or sound power. This value characterizes the perceived loudness of the sound. The absolute value of sound pressure is measured in pressure units - Pascals (Pa). The weakest sounds that our ear can perceive, the threshold of hearing, have an amplitude of 20 μPa, the strongest - 10 million times greater - 200 Pa.

Since the range of values ​​is too wide, it is inconvenient to use the absolute values ​​of the sound pressure (try to graph values ​​that differ by a factor of millions with acceptable accuracy). Therefore, in practice, the concept of sound level is used, measured in decibels (dB) and characterizing its relative strength.

The sound level is determined by the formula (where is the pressure of the measured sound, and is the hearing threshold), that is, as the decimal logarithm of the ratio of the absolute value of sound pressure to the value of the hearing threshold; based on some considerations, the logarithm is multiplied by 20. With this definition, the entire range of audible sounds fits into the scale of 0-140 dB; a difference of 1 decibel corresponds to a change in volume of about 10%, and the human ear is not able to catch a smaller difference.

The logarithmic scale, although unusual, is very close to human perception of sound. For example, a slight change in the strength of a soft sound will give the impression of a noticeable increase in volume, while a slight change in the volume of a loud sound will remain almost imperceptible. This fully corresponds to the mathematical description of the relative strength of sound using logarithms.

Some sound levels

The sound wave is well transmitted over the ground, so when we want to know if our train is going somewhere nearby, we put our ear to the rail. Sound can also travel through water - think about the sound channels in the oceans. And finally, he can come to us through the air. What exactly and how does it come to us?

A special organ called the ear is responsible for the perception of sound in the human body. Outside is the so-called outer ear, which passes into the ear canal about 0.6 cm in diameter and about 2.5 cm in length, ending tympanic membrane separating the outer and middle ear. Attached to the eardrum is a bone called the malleus. Together with the other two - the anvil and stirrup - they transmit the vibration of the tympanic membrane to the next snail-like membrane - the inner ear. This is a tube with a liquid with a diameter of about 0.2 mm and a length of 3-4 cm. Air vibrations are too weak to directly vibrate the liquid, but the middle ear, together with the tympanic membrane and the membrane of the inner ear, constitute a hydraulic amplifier: the area of ​​the tympanic membrane is many times larger than the inner membrane ear, so the pressure increases tenfold.

Inside the cochlea there is a membranous canal, also filled with liquid, on the lower wall of which is located the receptor apparatus of the auditory analyzer, covered with hair cells. Hair cells pick up fluctuations in the fluid that fills the canal. Each hair cell is tuned to a specific sound frequency, with cells tuned to low frequencies located in the upper part of the cochlea, and high frequencies are picked up by cells in the lower part of the cochlea.

Thus, movements of the stapes cause undulating vibrations in the fluid of the inner ear, which are picked up by hair cells located along the entire length of the cochlea and converted into electrical impulses. These electrical impulses are then transmitted along the auditory nerve to the brain.

The auditory nerve consists of thousands of the finest nerve fibers. Each fiber starts from a specific section of the cochlea and transmits a specific sound frequency. Low-frequency sounds, such as the sound of a car or train, are transmitted along fibers emanating from the top of the cochlea, and high-frequency sounds, such as the chirping of birds, are transmitted along fibers associated with its base. In this way, various sounds cause electrical excitation of various fibers in the composition of the auditory nerve. It is these differences that the brain is able to perceive and interpret.

In addition to the perception of light, color and sound, the issues of their fixation are important for the development of mankind. Unfortunately, we learned to record sound much later than to save images: Thomas Alva Edison invented the phonograph, which was used to record and read on wax cylinders with a metal needle sound information, only in 1877.

The device of modern digital audio recording facilities is based on the most important aspect of the mathematical description of sound - the Kotelnikov-Nyquist-Shannon theorem, otherwise called the sampling theorem. The essence of the theorem is that in order to obtain a high-quality sound recording, a digital device must record sound at least twice as often as the frequency of this sound.

For example, the simplest mobile phones, voice recorders, answering machines are designed to transmit or record a person's voice, the frequency spectrum of which is not more than 3 kHz. Therefore, a person's speech is recorded by an answering machine as an electrical signal 8-11 thousand times per second (in other words, a sampling frequency of 8-11 kHz is used). As another example, the highest human-perceptible sound frequency is 20 kHz, so in order to guarantee the quality of any audio material, the Audio CD standard uses a sampling rate of 44.1 kHz.

Another important characteristic of sound is its spectrum, obtained as a result of the decomposition of sound into simple harmonic vibrations (the so-called frequency analysis of sound). The spectrum is continuous, when the energy of sound vibrations is continuously distributed over a more or less wide frequency range, and linear, when there is a set of discrete (discontinuous) frequency components. Sound from continuous spectrum perceived as noise, such as the rustle of trees in the wind, the sounds of working mechanisms. Musical sounds have a line spectrum with multiple frequencies; the fundamental frequency determines the pitch of the sound perceived by the ear, and the set of harmonic components determines the timbre of the sound.

The possibility of sound recording allows a person to store, process and transmit the sounds of our world to descendants.

Understanding exactly how we see and hear, realizing that our multi-colored and many-voiced worlds are individual, and therefore unique, knowing that the world around us is only ours and no one else's - after all, other worlds are colored differently and sound differently; hearing rain and seeing a rainbow in front of us, remember that all this is just waves. And only we endow them with meaning, beauty and sound.

Have you ever tried holding a shell to your ear? Remember? .. This is how we sound.