The chemical composition of the substance- the most important characteristic of the materials used by mankind. Without his exact knowledge, it is impossible to plan technological processes in industrial production with any satisfactory accuracy. Recently, the requirements for determining the chemical composition of a substance have become even more stringent: many areas of industrial and scientific activity require materials of a certain "purity" - these are the requirements for an exact, fixed composition, as well as a strict restriction on the presence of impurities of foreign substances. In connection with these trends, more and more progressive methods for determining the chemical composition of substances are being developed. These include the method of spectral analysis, which provides an accurate and fast study of the chemistry of materials.

fantasy of light

The nature of spectral analysis

(spectroscopy) studies the chemical composition of substances based on their ability to emit and absorb light. It is known that each chemical element emits and absorbs a light spectrum characteristic only for it, provided that it can be reduced to a gaseous state.

In accordance with this, it is possible to determine the presence of these substances in a particular material by their inherent spectrum. Modern methods of spectral analysis make it possible to establish the presence of a substance weighing up to billionths of a gram in a sample - the indicator of radiation intensity is responsible for this. The uniqueness of the spectrum emitted by an atom characterizes its deep relationship with the physical structure.

Visible light is radiation from 3,8 *10 -7 before 7,6*10 -7 m responsible for different colors. Substances can emit light only in an excited state (this state is characterized by an increased level of internal ) in the presence of a constant source of energy.

Receiving excess energy, the atoms of matter emit it in the form of light and return to their normal energy state. It is this light emitted by the atoms that is used for spectral analysis. The most common types of radiation include: thermal radiation, electroluminescence, cathodoluminescence, chemiluminescence.

Spectral analysis. Flame coloring with metal ions

Types of spectral analysis

Distinguish between emission and absorption spectroscopy. The method of emission spectroscopy is based on the properties of elements to emit light. To excite the atoms of a substance, high-temperature heating is used, equal to several hundred or even thousands of degrees - for this, a sample of the substance is placed in a flame or in the field of powerful electric discharges. Under the influence of the highest temperature, the molecules of a substance are divided into atoms.

Atoms, receiving excess energy, radiate it in the form of light quanta of various wavelengths, which are recorded by spectral devices - devices that visually depict the resulting light spectrum. Spectral devices also serve as a separating element of the spectroscopy system, because the light flux is summed from all substances present in the sample, and its task is to divide the total light array into spectra of individual elements and determine their intensity, which will allow in the future to draw conclusions about the value of the element present in the total mass of substances.

• Depending on the methods of observing and recording spectra, spectral instruments are distinguished: spectrographs and spectroscopes. The former register the spectrum on photographic film, while the latter make it possible to view the spectrum for direct observation by a person through special telescopes. To determine the dimensions, specialized microscopes are used, which allow to determine the wavelength with high accuracy.
• After registration of the light spectrum, it is subjected to a thorough analysis. Waves of a certain length and their position in the spectrum are identified. Further, the ratio of their position with belonging to the desired substances is performed. This is done by comparing the data of the position of the waves with the information located in the methodical tables, indicating the typical wavelengths and spectra of chemical elements.
• Absorption spectroscopy is carried out similarly to emission spectroscopy. In this case, the substance is placed between the light source and the spectral apparatus. Passing through the analyzed material, the emitted light reaches the spectral apparatus with "dips" (absorption lines) at certain wavelengths - they constitute the absorbed spectrum of the material under study. The further sequence of the study is similar to the above process of emission spectroscopy.

Discovery of spectral analysis

Significance of spectroscopy for science

Spectral analysis allowed humanity to discover several elements that could not be determined by traditional methods of registering chemicals. These are elements such as rubidium, cesium, helium (it was discovered using the spectroscopy of the Sun - long before its discovery on Earth), indium, gallium and others. The lines of these elements were found in the emission spectra of gases, and at the time of their study were unidentifiable.

It became clear that these are new, hitherto unknown elements. Spectroscopy has had a serious impact on the formation of the current type of metallurgical and machine-building industries, the nuclear industry, and agriculture, where it has become one of the main tools for systematic analysis.

Spectroscopy has become of great importance in astrophysics.

Provoking a colossal leap in understanding the structure of the universe and asserting the fact that everything that exists consists of the same elements, which, among other things, abound on the Earth. Today, the method of spectral analysis allows scientists to determine the chemical composition of stars, nebulae, planets and galaxies located billions of kilometers from the Earth - these objects, of course, are not accessible to direct analysis methods due to their great distance.

Using the method of absorption spectroscopy, it is possible to study distant space objects that do not have their own radiation. This knowledge makes it possible to establish the most important characteristics of space objects: pressure, temperature, features of the structure of the structure, and much more.

2.1. Modern model of the nature of light

A physical body whose temperature is above absolute zero radiates radiation energy into the surrounding space, and the body itself is called an emitter. Energy is emitted both by natural emitters (the Sun, stars, bioorganisms) due to various physical processes taking place in them, and artificial emitters due to thermal, electrical, mechanical and other types of energy applied to them, causing heating of the physical body.

Energy is radiated into the surrounding space in the form of elementary particles - photons, each of which has a quantum of energy. Consider in Figure 1.2.1 a simplified scheme of energy radiation.

Rice. 1.2.1 - Simplified scheme of radiation of radiant energy.

It is known that an atom of a substance consists of a nucleus and electrons interconnected by electromagnetic forces. Electrons are at certain energy levels. The level closest to the nucleus, at which electrons are located when the atom is at rest, is called the ground level ( O) corresponding to the minimum fraction of energy. The rest of the levels farthest from the nucleus are excited ( AT). For the transition of electrons from the ground level to excited ones, it is necessary to impart additional energy to the electrons and to the whole atom as a whole ( W). Absorbing the applied energy, the atom comes into an excited state and the electrons move away from the nucleus of the atom to higher energy levels (excited levels). The greater the applied energy, the higher the electrons are removed. But this state is unstable, and due to electromagnetic attraction, the electrons tend to return to the ground level. During the transition of electrons from one energy level to another, a minimum portion of radiant energy is released W f \u003d Q – quantum carried by a photon.

A photon has a finite mass and speed and exists only in motion. Absorbing energy, the atom absorbs photons, which cease to exist, and their energy is transferred to the atom. When energy is emitted, an atom creates a photon and its energy is formed by the atom. Photons are emitted into space and absorbed by bodies in separate portions, i.e. discretely, and this discreteness determines the frequency of radiation. The movement of photons in space occurs in the form of waves of harmonic sinusoidal electromagnetic oscillations, which are characterized by a number of values ​​(Fig. 1.2.2):

The wavelength that determines the distance between two points that are in the same phase of a wave oscillation. The wavelength is denoted λ and is measured in meters m). For light emissions, wavelengths are usually given in nanometers (nm). The nanometer is a convenient international unit and is equivalent to a millimicron. Table 1.2.1 shows the relationship between different units of length and they can easily be converted to each other.

Table 1.2.1.

Frequency, which determines the number of wave oscillations per unit time. The frequency is denoted ν and measured in hertz (Hz).

The period of oscillation, which determines the time during which a complete wave oscillation occurs. The period is denoted T and is measured in seconds ( with).

The period is the reciprocal of the frequency:

T=1/v , with (1.2.1)

The frequency of oscillations and the wavelength of electromagnetic radiation are interconnected by the following relationships:

ν \u003d C o /λ, Hz or λ= C o / ν, m, (1.2.2)

where C o- the speed of propagation of electromagnetic waves of any length in vacuum, is a constant value and is equal to the speed of propagation of light 2.9979 10 8 ≈ 3 10 8 m/s.

Fig.1.2.2. Scheme of sinusoidal oscillations with different wavelengths, where λ2 >λ1 defining T 1 - period, time of photon movement from point 1 to point 3 and T 2 - period, time of photon movement from point 1 to point 4; along the Y~W y-axis.

The energy of a photon - a quantum, according to Planck's formula, depends on the frequency of electromagnetic oscillations:

W f \u003d h· ν , J,(1.2.3)

where h= 6.626 10 -34 J s- a constant coefficient derived by the physicist M. Planck and called Planck's constant.

The physical nature of all types of electromagnetic radiation is the same, that is, in all cases, the energy propagates in the form of electromagnetic waves of different lengths, which correspond to electromagnetic oscillations of different frequencies. A simple electromagnetic wave contains electric and magnetic waves that are perpendicular to each other, but oscillate in the same phase (Fig.1.2.3).

Fig.1.2.3 - Modular image of a simple electromagnetic wave ( a) and the type of wave packet (along the axis z) coinciding in phase ( b).

They oscillate in a direction perpendicular to the axis z, which is called the wave propagation vector. The speed of light refers to the speed at which light travels in the direction of propagation (direction z). Electric and magnetic waves are also often described by vectors. The electric field vector of the wave interacts with the electric fields in atoms, and therefore it is very important for the subsequent presentation of the material.

Following the wave model, the intensity of the light flux can be determined by the square of the amplitude a electric vector (Fig. 1.2.3), i.e.

I = ka 2, (1.2.4)

where k- constant. Therefore, the larger the wave amplitude, the more intense the radiation. However, in the corpuscular theory of light, the amplitude does not matter, since the model is based on the concept of photons. Therefore, another way of describing the intensity of light is needed. In the corpuscular model, the intensity of light is proportional to the number of photons per unit volume of the light flux, or, in other words, is proportional to the "photon density". It can be shown that both concepts of intensity - density and amplitude - are consistent with each other and equation (1.2.4) is valid regardless of the light model used. The intensity of light can be spoken of as a flux of photons or the amplitude of a wave. Both concepts are used depending on their application.

The magnetic vector of electromagnetic radiation is not of such interest here as the electric vector, since only the electric vector can interact with electrons and electric fields in an atom or molecule. This electrical vector interaction causes wave reflection, refraction, and transmission, as well as color, chemical reactions, and heating in most substances. All these phenomena will be considered in other sections of the book.

Expression hv often used in the description of chemical reactions to indicate that a photon of electromagnetic radiation is necessary for their occurrence. For example, a reaction important to human vision involves light-induced isomerization of the vitamin BUT, contained in the retina of the eye. Value hv characterizes the energy of light and does not violate the mass balance of a chemical reaction.

2.2. Radiant energy and radiant flux.

The energy emitted in the region of the optical spectrum of radiation is called radiant energy or radiation energy and denote W e(you can also meet the designation of energy with the letter Q). If the energy is transferred by the entire set of wavelengths that make up the radiation, then it is called integral and is measured in the same units as other types of energy ( joule, electron volt).

The total power carried by electromagnetic radiation, regardless of its spectral composition, is called in lighting engineering radiation flux or radiant stream, denoted Fe and is measured in watts Tue):

F e = W e /t, Tue. (1.2.5)

2.3. Spectral composition of optical radiations.

The general spectrum of electromagnetic radiation can be divided into a number of main areas:

1. Region of cosmic radiations.

2. Region of gamma radiation.

3. The region of X-rays.

4. The region of the optical spectrum of radiation.

5. Radio wave region.

6. Ultrasonic and sonic area.

7. Force area.

The region of optical radiation corresponds to electromagnetic waves with a wavelength of 1 nm up to 1 mm and it can be divided into three regions: ultraviolet (UV), visible and infrared (IR).

The ultraviolet region of optical radiation lies within 1 ... 380 nm. The International Commission on Illumination (CIE) has proposed the following division of UV radiation with wavelengths from 100 nm up to 400 nm: UV-A - 315…400 nm; UV-B - 280…315 nm; UV-C –100…280 nm.

Visible radiation (light), falling on the retina of the eye, as a result of the conscious transformation of the energy of an external stimulus, causes a visual sensation. The wavelength range of the monochromatic components of this radiation corresponds to 380 ... 780 nm.

The wavelengths of the monochromatic components of infrared radiation are greater than the wavelengths of visible radiation (but not more than 1 mm). The CCO proposed the following division of the IR radiation area: IR-A - 780 ... 1400 nm; IR-V – 1400…3000 nm; IR-S - 3000 nm (3 Mkm)…10 6 nm (1mm).

It is these three areas of optical radiation that are of greatest interest to lighting engineering. But practically all electromagnetic radiations, to one degree or another, affect the atoms and molecules of various substances. Table 1.2.2 summarizes the phenomena that occur in molecules when exposed to electromagnetic radiation of various wavelengths.

Table 1.2.2.

All the energies of electromagnetic radiation, which simultaneously irradiate the Earth, reproduce only celestial phenomena. However, in terrestrial conditions, if it is necessary to reproduce radiation in a wide range of energies, it is necessary to have several sources of energy; for example, a phenomenon in which X-rays are produced does not simultaneously excite radio waves, and vice versa. It should be noted that the phenomena listed in Table. 1.2.2 as an example of the reactions of molecules when exposed to different energy bands on a substance, it is often convenient to use in order to reproduce this energy. So, visible light will call low-energy electronic excitations in the valence shell of an atom, however, it can be reproduced by electronic removal of excitation in the valence shell of an atom during its transition from higher levels down to the ground state.

The lowest energy type of electromagnetic wave is found in generators used to generate electrical current. In Ukraine, the frequency of industrial electrical alternating current is standardized and equal to 50 Hz. This frequency reproduces the wavelength 6 10 6 m. The so-called sonic and ultrasonic range of electromagnetic radiation is used in audio and ultrasonic technology.

Radio waves are the lowest energy electromagnetic waves that can have a direct effect on individual atoms. However, the energy of these waves is so small that it can only move entire molecules a short distance in space (translation) and reorient some of the nuclei in relation to other nuclei in the molecules. The latter effect underlies the spectroscopic method of nuclear magnetic resonance. The energies corresponding to the microwave region cause the gas molecules to rotate around their centers of mass and also change the mutual orientation of the electrons. The first effect is the basis of microwave spectroscopy used to study molecular rotations, the second is the basis of electron spin resonance spectroscopy used to study the state of unpaired electrons in chemical systems.

The energies corresponding to the infrared region enter into resonance with the vibrations of atoms in chemical bonds. This effect is used in infrared spectroscopy. The energies of the visible and ultraviolet regions can cause the excitation of electrons in atoms and molecules with their transfer from lower energy states to upper ones. As the energy of the beams increases, the excited electrons move to a new state from more stable energy levels. Visible absorption spectroscopy deals with the excitation of electrons from the outermost shells of atoms and molecules, while ultraviolet absorption spectroscopy deals with excitations of higher energy electrons from both outer and inner shells. X-ray radiation causes excitations of electrons in the inner electron shells, since it has a wavelength that is close to the size of the atoms themselves. Atoms can cause X-ray diffraction. Excitation is at the heart of X-ray spectral fluorescence analysis and X-ray photoelectron spectroscopy (ESCA), while diffraction is used to identify the crystal lattice and determine the crystal structure. Gamma rays are suitable for the application of electromagnetic radiation with the highest energy. They cause the excitation of nuclei with their transfer from lower energy states to higher ones and underlie Mössbauer spectroscopy.

Much of the energy range of electromagnetic radiation has important applications in physics, chemistry and biology.

However, with regard to works of art and lighting materials, the most important are medium energies (ultraviolet, visible and infrared) due to the fact that they affect them. If we sequentially arrange ultraviolet, visible and infrared radiation, we will get a more detailed classification (Fig.1.2.4).

Fig.1.2.4 - Expanded region of the spectrum of electromagnetic radiation.

Powerful ultraviolet and infrared radiation have a harmful effect on humans: ultraviolet causes burns to the skin and eyes, and infrared makes work difficult due to the large amount of heat generated.

2.4. Ultraviolet radiation.

In the electromagnetic spectrum of radiation, the ultraviolet region occupies an intermediate position between visible light and X-rays.

Ultraviolet radiation was discovered by I. V. Ritter in 1801, who in his experiments used sunlight, a glass prism and a plate coated with silver chloride. Silver halogens are sensitive to UV radiation. Ritter found that the plate darkened first outside the violet end of the spectrum, then in the violet region, and finally in the blue region, which served as evidence for the existence of radiation with wavelengths shorter than those of the violet rays. This range of wavelengths, invisible to the eye, was called ultraviolet. Currently, the ultraviolet range is defined approximately as the region of wavelengths 1–400 nm. For convenience, this area is sometimes subdivided into smaller sections.

Range 1–180 nm called vacuum ultraviolet due to the fact that such radiation is transmitted only by vacuum. This short-wavelength part of ultraviolet radiation, especially with wavelengths shorter than 120 nm, almost completely absorbed by all known materials and media, including air.
Range 180–280 nm called shortwave or far ultraviolet (far region of the ultraviolet spectrum). In this range of radiation, quartz and photographic gelatin pass through. Emissions in the far region have the property of ozonizing the air and
kill bacteria. The same region of ultraviolet radiation is used in gas-luminous luminescent light sources to obtain bright fluorescence of luminous compounds that cover the tubes (on the inside) of fluorescent lamps.

Wavelength range 280–300 nm known as medium ultraviolet. These radiations are characterized by the ability to cause redness and sunburn of human skin, as well as a beneficial effect (in certain doses) on the growth and development of animals and plants.

Range 300–400 nm called long-wave or near ultraviolet (near ultraviolet spectrum) and it is these radiations that ordinary glass transmits. With the exception of the sun and mercury discharge tubes, ultraviolet radiation cannot be produced by sources commonly used to produce visible light. The region of ultraviolet radiation closest to the visible spectrum (320–400 nm) contains rays that are widely used for luminescent analysis, as well as for excitation of luminous substances in luminescent photography and filming.

An important feature of ultraviolet rays that distinguish them
from X-rays and other, shorter-wavelength radiations, is that they are refracted at the interface between media with different densities and reflected from mirror surfaces. This makes it possible to focus them with a lens made of materials that transmit ultraviolet rays (fluorite, quartz glass, to some extent optical glass) and obtain a real ultraviolet invisible image that can be fixed on photographic film and thus made visible.

The most powerful natural source of ultraviolet radiation is the sun. However, only ultraviolet rays with a wavelength of at least 290 reach the earth's surface. nm. Shorter wavelength ultraviolet rays are completely absorbed by ozone, which is contained in a relatively large amount in the stratosphere. The spectral distribution of ultraviolet radiation depends on the height of the sun above the horizon. The closer the sun to the horizon, the less ultraviolet rays in the sunlight. At a sun height of 1° above the horizon, solar radiation reaching the earth's surface does not contain radiation with wavelengths shorter than 420 nm, that is, ultraviolet rays in the radiation spectrum of the rising and setting sun are completely absent.

The main artificial sources of ultraviolet radiation in all parts of the ultraviolet region of the spectrum are high-pressure mercury lamps and ultra-high-pressure mercury lamps.

Radiation in the wavelength range 200–400 nm is predominant, it causes photochemical reactions and bond breaking in many organic compounds. However, these photochemical reactions also have a positive side. Artists know that by exposing a freshly painted object to daylight, they speed up the drying and oxidation of oils, and that this must be done before varnishing it. Ultraviolet radiation can be used in the study of films of paints and varnishes to prove the corrections made. Under the action of ultraviolet radiation, organic compounds often affect each other's fluorescence. For example, mastic resin and dammar resin in old varnish give a yellow-green fluorescence, the intensity of which can change over time. Fresh artificial varnish does not fluoresce. Wax fluoresces bright white and shellac fluoresces orange. With increasing service life, the fluorescence intensity of automotive paints often tends to increase. Under ultraviolet light, recent corrections in paintings appear purple or black. However, over the years they become grayer, while the unvarnished areas of dark paint are a deep purplish brown. Under ultraviolet light, the damage on the paper covered with brown (“fox”) spots becomes obvious, as well as changes and erasures on old paper. Materials such as minerals, bones, and teeth fluoresce when exposed to ultraviolet light. Faux jewelry that looks exactly like the real thing in daylight may look completely different under ultraviolet light. However, ultraviolet radiation is very harmful to many works of fine art.

Powerful ultraviolet radiation has a harmful effect on humans and causes burns to the skin and eyes.

It should be noted that the division of the ultraviolet spectrum into the listed regions is conditional, since the properties of ultraviolet rays characteristic of one region of the spectrum are partially inherent in neighboring regions, although to a lesser extent.

2.5. visible radiation.

Almost all representatives of the animal world have the ability to “see” something. The human eye only responds to a tiny fraction of the electromagnetic spectrum. This area is called visible. It is accepted that for the human eye the range of visible wavelengths occupies the interval from 380 to 780 nm. However, this area is not visible to all animals and insects. For example, bees can see in the near ultraviolet region. This gives them the ability to perceive differences in colors that are inaccessible to human vision. The reaction of the human eye and brain to different wavelengths and light intensity varies in the range of 380 - 780 nm and this gives sensations called color, texture, transparency, and so on. a mixture of individual colors (Fig. 1.2.5). As for the human eye, such a combination of individual monochromatic radiations is possible, when only the impression of white light is created, although it may not be so in terms of spectral composition.

Rice. 1.2.5 - Decomposition of "white" visible light into spectral components with different wavelengths from red (K) to violet (F).

Color and its origins have occupied the imagination of many great naturalists. However, only I. Newton managed to develop the foundations of color theory. In 1672, Newton experimentally showed that a beam of white light passing through a glass prism decomposes into a spectrum consisting of a large number of colors (from red to violet), which gradually change one to another at the transition points. These colors are constituents, not modifications, of white light. Rice. Figure 1.2.5 illustrates this well-known property of transparent materials and light. The explanation for Newton's experimental observations with a prism lies in the fact that light of all wavelengths travels at the same speed only in a void - vacuum. However, in any other medium, light of different wavelengths travels at different speeds. As a result, wave separation may occur. The decomposition of white light by a medium into different colors, or, equivalently, into different wavelengths, is called dispersion. It is thus convenient to subdivide the visible range according to the different color response elicited in the human eye into seven intervals ranging from the longest to the shortest wavelength. These intervals correspond to red, orange, yellow, green, blue, indigo and violet.

Since when the visible (white) light is decomposed by a prism into a continuous spectrum in the latter, the colors smoothly pass one into another, it is difficult to accurately determine the boundaries of each color and associate them with a specific wavelength. But roughly they look like this:

purple - 380 ... 440 nm;

blue - 440…480 nm;

blue – 480…510 nm;

green – 510…550 nm;

yellow-green - 550 ... 575 nm;

yellow - 575 ... 585 nm;

orange - 585…620 nm;

red - 620…780 nm.

Electromagnetic radiation with a wavelength of more than 700 nm and less than 400 nm practically no longer perceived by the eye and therefore quite often in the popular literature it is in this range that the limits of visible radiation are set, which does not correspond to the actual situation.

Happening normal dispersion shown in fig. 1.2.5. It is observed for a colorless transparent medium. This kind of dispersion is called normal because red light (the longest wavelength) has the highest speed and the least dispersion, while violet light (the shortest wavelength) has the slowest speed and the most dispersion. Between red and purple, other colors are sequentially placed. More precisely, the dispersion of visible light changes with wavelength approximately according to the law 1/λ 3 . For this reason, the shortest wavelengths have the greatest dispersion (1/λ 3 increases) and a large degree of its change with small variations (the function 1/λ 3 is non-linear in λ) compared to long waves. It should be mentioned that another type of separation of light by wavelength, called anomalous dispersion, observed in a colored medium. In the region of the spectrum in which light is absorbed, with anomalous dispersion, the longest waves have a greater dispersion than the short ones. Therefore, the sequence of colors in accordance with Fig. 1.2.5 is not observed. Visible light can also cause many chemical reactions.

The mechanism of perception of visible radiations is described in detail in §4.

2.6. Infrared radiation.

Infrared rays are invisible, they are not perceived by the human eye. It is possible to detect their presence and action only in various indirect ways. The existence of radiation beyond the red region of the visible spectrum was discovered as early as 1800 by William Herschel. He noticed that a blackened thermometer placed in the spectrum of sunlight detects a significant increase in temperature. This experiment revealed that there are invisible waves in nature, with a wavelength longer than red, and this radiation became known as infrared. Of course, the effects of infrared radiation have been known since ancient times. After all, infrared radiation caused by the flame of a fire was one of the phenomena that had the greatest impact on the development of mankind. Near infrared rays adjacent to the long wavelength end of the visible part of the spectrum can be recorded photographically. Infrared photography has been used since 1925, when sensitizers were obtained that sensitive photographic emulsion to the infrared region of the spectrum. The energy range of infrared radiation occupies a wide area, starting from the low-energy side of the visible spectrum, i.e. the real infrared region lies outside the red part of the visible spectrum, starting from λ= 760 nm(dark red potassium line) and propagates further towards longer wavelengths. Area from λ=760 nm up to λ=3500 nm is an area of ​​practical applications of infrared radiation.

There are various methods for obtaining an image in infrared rays: with the help of electron-optical converters, methods based on the properties of infrared rays to quench phosphorescence, act on the photographic layer and have a thermal effect.

Based on the theory of photochemical reactions, it can be assumed that infrared photography, based on the sensitization of photographic materials, is hardly feasible in rays with a wavelength of more than 2000 nm.

Infrared radiation causes thermal effects that can mechanically or chemically change materials, while photochemical mechanisms rarely lead to such changes. When exposed to infrared radiation, wood, glass and ceramics undergo mechanical changes such as shrinkage, cracking and drying. Not to mention the enormous damage that infrared radiation can cause on wax objects. If chemical changes occur, they are usually an indirect result of infrared radiation. If a chemical reaction is already taking place, then whether it is slow or fast, the heat from exposure to infrared radiation will always speed up the reaction. Yellowing of natural lacquer films can be a direct result of exposure to infrared radiation. However, artificial lacquer films are usually not sensitive to infrared radiation.

Infrared radiation is used in infrared photography, which is an important method for conducting research on works of art in museums, art galleries. In some cases, infrared rays can penetrate visually opaque varnishes and thin paint films and, using image intensifier tubes, thermal imaging equipment, and infrared photography, reveal tinting, drawings or corrected areas. Those. infrared radiation can be used to view images through opaque films because it has longer wavelengths than visible radiation. At the same time, infrared radiation is scattered in the lacquer film by small particles much less than visible light. Therefore, infrared rays can penetrate the upper layers and overcome their opacity. It becomes possible to observe the details of the drawing in a layer of paint that has darkened from old varnish and dirt. Sometimes fakes can be detected in this way, since the bottom layer of paint is different from what is on the surface.

The photographic method of fixing an image formed by infrared rays is based on some properties of infrared radiation:

1. Infrared rays are less susceptible to scattering in the atmosphere, as well as in turbid environments in general. They pass through air haze and light fog better than visible light rays. This makes it possible to shoot objects that are at a great distance, overcoming the air haze.

2. Absorption and reflection of infrared rays is different than the rays of the visible region of the spectrum. Therefore, many objects that appear the same in color and brightness in visible light, in a photograph taken in infrared rays, have a completely different distribution of tones. This allows you to detect many interesting and important features of the captured object. For example, chlorophyll, found in living green foliage and grass, strongly absorbs short-wavelength visible rays and reflects most of the infrared rays. In addition, by absorbing ultraviolet
summer rays, chlorophyll fluoresces in the infrared region. As a result, in photographs taken on infrachromatic film using a red filter, greens come out unnaturally white and blue skies look dark. Many colors that appear very bright to the eye, due to their almost complete absorption of infrared rays, turn out to be almost black on infrachromatic film.

3. Infrared rays are capable of penetrating media that are opaque to visible light. Human skin, thin layers of wood, ebonite, dark shells of insects and plants, etc. are transparent to infrared rays.
Blood vessels are clearly visible through the skin, which is transparent to infrared rays.

4. Because infrared rays are invisible, shooting under infrared light is essentially shooting in the dark. Such photography or filming is necessary in cases requiring dark adaptation of the eyes, as well as in all kinds of psychological research.

At present, filming in infrared rays is used both in scientific cinematography and in the production of films to solve some visual problems, to shoot "day to night", to create combined frames against the background of an infrared screen - the "wandering mask" method, etc.

The powerful infrared radiation of some lighting fixtures makes it difficult for the crew to work due to the large amount of heat generated.

2.7 Types of spectra

The spectra of light sources are obtained by decomposing their radiation in terms of wavelengths ( l) spectral devices and are characterized by the distribution function of the energy of the emitted light depending on the wavelength. The radiation of a radiant flux along the spectrum of radiation can occur with one wavelength, with several wavelengths, and also continuously in separate sections or throughout the entire region of the optical spectrum of radiation.

Monochromatic(from Greek. monos- one, one and chốma- color) radiation is radiation with one frequency or wavelength. Radiation in the wavelength range up to 10 nm called homogeneous. The totality of monochromatic or homogeneous radiation forms range.

There are continuous (continuous), striped, line and mixed spectra. solid(continuous) spectra are those in which the monochromatic components fill without breaks the wavelength interval within which radiation occurs. Such a spectrum is typical for incandescent lamps (Fig. 1.2.6) and other heat emitters.

Rice. 1.2.6 - Continuous spectrum of incandescent lamps

Rice. 1.2.7 - Line spectrum from monochromatic radiations

Rice. 1.2.8 - KinoFlo KF55 mixed spectrum fluorescent lamp

Rice. 1.2.9 - The complex spectrum of the KinoFlo Green fluorescent lamp

Ruled spectra consist of separate monochromatic radiations not adjacent to each other (Fig. 1.2.7), and mixed contain a combination of spectra (Fig.1.2.8). AT striped spectra, monochromatic components form discrete groups (bands) in the form of many closely spaced lines. This type of radiation is also called difficult(Fig.1.2.9). Striped, line, and mixed spectra are characteristic of arc and gas-discharge light sources.

Of the entire spectrum of radiation from light sources, only visible light, acting on the light-sensitive elements of the eye, causes a visual sensation. Homogeneous, monochromatic visible radiation, entering the eye, causes the sensation of light of a certain color.

System of light values

A fuzzy idea of ​​certain light quantities is often the cause of serious errors that specialists make when designing and operating lighting systems.

Knowledge of light values ​​is necessary for students and professionals working in television, video or film studios, and even amateurs who shoot home video. This will help you to navigate correctly in the abundance of light sources, light filters, lighting fixtures, to understand the functions of video cameras related to light sensitivity, contrast and color reproduction.

Since the light quantities, which are a numerical characteristic of light radiation, come from energy photometric quantities, it is advisable to consider them together, based on the primacy of the latter. Photometric quantities and units are those that characterize optical radiation. The term "photometry" is formed from two Greek words: "phos" - light and " metreo " - I measure, and means light measurements. There are energy photometric and reduced photometric systems of quantities.

Energy quantities– characterize the radiation irrespective of its effect on any radiation receiver. Energy quantities such as radiant energy ( We ) and radiant flux ( Fe ) were discussed in the previous section. They are expressed in units derived from the unit of energy ( Joule), and their designations use the additional index “ e» ( W e , F e , I e , E e , L e ).

Reduced or effective photometric quantities characterize the radiation incident on a given selective radiation detector. If the human eye serves as such a receiver, then the values ​​obtained are called " light", and their totality is " system of light values". In the letter designations of light quantities, you can find the index "v".

The scheme of the formation of a system of light quantities based on energy ones is shown in fig. 1.3.1.

Rice. 1.3.1 - Scheme for the formation of a system of light quantities

Each of the light quantities of quantities has its own energy fundamental principle, from which they are derived:

· Light flow F (F v,F v ) - the fundamental principle of the radiant flux (radiation flux) Fe (F e)

· The power of light I (I v ) - energy radiation force (radiation strength) I e

Illumination E (E v ) - energy illumination (irradiance) E e

Brightness L (L v ) – energy brightness Le

These and other basic energy and light quantities are summarized in the table at the end of the section. Below, the main light quantities used in the practice of a cameraman will be considered in detail.

Similar information.

Photography takes place both in natural daylight and with artificial light sources: incandescent lamps, gas-discharge flash lamps, flash lamps, etc. All these sources differ greatly from each other in terms of the spectral composition of light. The choice of a light source is influenced not only by specific conditions shooting, but also the lighting characteristics of the sources. If, when shooting on black and white film, attention is primarily paid to the intensity of the luminous flux of the light source and, to a lesser extent, to its spectral composition, then when shooting on color film, the spectral composition of the light is of decisive importance. The transmission of tonal colors when shooting on black-and-white film and natural colors when shooting color, the choice of color-sensitive material and light filters depends on the spectral composition.

When the color of the light source changes, the tone scale that conveys the colors of the object also changes. The spectral composition of light, its color temperature must be balanced with the color sensitivity of the negative material. Only in this case the correct color rendition is possible.

Daylight belongs to the group of temperature light sources.

The earth's surface and everything on it is illuminated either by mixed, total light (total radiation) of direct solar and diffuse radiation coming from the sky and clouds, or in cloudy weather, when the sun is covered by clouds, by diffused sky light. Places where direct sunlight does not penetrate are illuminated only by the diffused light of the sky (Fig. 6).

And from the table. Figure 3 shows how the spectral composition of solar radiation changes depending on the height of the sun.

The sun rises especially fast in the morning and goes down in the evening. Approximate changes in color temperatures throughout the day and depending on the state of the sky are given in Table. 4.

But the pattern of fluctuations in the spectral composition and intensity of daylight radiation is continually violated due to changes in meteorological conditions occurring in the atmosphere (cloudiness, height, degree and density of which are very unstable, humidity and dustiness of the air, haze, fog, etc.). These random variable factors are so closely related and intertwined that it is very difficult to take into account the influence of each of them.

When the sun rises above the horizon or sets, it looks like a red ball with a color temperature of about 1800 K. At this time, on the way to the earth, the sun's rays penetrate the air shell surrounding our planet and travel the longest path in the atmosphere. The length of the path of sunlight in the atmosphere is of great importance, especially for the short-wavelength part of the spectrum. In the stream of the sun's rays, which have passed the longest path in the air, there are no blue-violet rays: they are filtered out by a layer of air, which, by changing the spectral composition of sunlight, acts as a yellow filter of variable density. During partial cloud cover, when the sun shines through clouds or is in a haze, the short-wave part of the radiation also weakens.

Solar radiation as a result of multiple reflections by the molecules of the gases that make up the air undergoes molecular scattering. The visible color of the air layer above the earth, the color of the sky and are explained by the strong molecular scattering of the short-wave part of solar radiation. Molecular scattering is the cause of airborne blue haze.

As a result of the scattering of part of the sunlight by the atmosphere, the sky itself becomes a light source (secondary) with a clearly defined color. In the spectrum of the blue sky, a significant predominance of blue and violet colors is observed; all other colors are also contained, but to a much lesser extent (Fig. 6, curve 3).

Diffused skylight also experiences strong color temperature fluctuations, depending on whether the light comes from a blue, cloudless sky or from a sky covered in haze or clouds.

Mechanical impurities are constantly suspended in various amounts in the air - turbid particles (air in thick layers can be considered as a turbid medium): dust particles raised by ascending air currents and wind, small drops of water, water vapor, which contribute to the appearance of haze. Quantity decreases with height - they do not rise above 1000 m. as a result, the sky acquires a whitish color.The increased humidity of the air also contributes to the whitening of the sky, which causes the formation of haze, white with a blue tint.

When clouds appear, white light reflected from the clouds is added to the light of the sky. Large drops of water that make up clouds scatter the rays of the entire spectrum.

Near large cities, due to the high dustiness of the lowest layers of the air, the appearance of fumes, smoke and dust in them, the sky near the horizon turns gray or white in different shades.

As the sun rises higher and the path of the rays in the atmosphere becomes shorter, the radiation from red, reddish through yellow turns into yellowish. At the same time it changes its color and the sky. Bluish at first, it turns reddish near the sun at sunrise and sunset, and turns into blue as the sun rises. If the air is transparent, the sky becomes blue.

Shortly after sunrise and shortly before sunset, the color temperature rises to 3000-3200K, which makes it possible to shoot on LN-type color film. About an hour after sunrise, at the height of the sun, its color temperature rises to 3500 K. Radiation at this time consists of half red, one quarter yellow rays, and the remaining quarter is green, blue and violet. The shadows, starting from the longest, rapidly decrease, and at a sun height of 15 ° become almost equal to four times the length of the object. In the afternoon, when the sun drops below 13-15q, and as it moves further towards the horizon and the blue-violet rays weaken, the radiation acquires distinct shades from yellow to red. The shadows also become longer. Horizontal surfaces at this time are illuminated mainly by the sky and, under the influence of the increasing effect of the scattered light of the sky, turn blue, and vertical ones are more illuminated by the yellow light of the sun.

The path traversed by its rays in the atmosphere is greatly shortened and most of the short-wave radiation reaches the earth's surface. The total light of the sun and the sky with a cloudless sky stabilizes, becomes white and almost does not change with the height of the sun at this time of day.

This is the best time to shoot, especially on DC color film, balanced for a color temperature of 5600-5800 K. Even if some changes in the color temperature of light occur at this time, they do not matter at all for black and white shooting, but for color are not so significant as to noticeably worsen the color rendition. The change in the color temperature of daylight during the day is shown in Fig. 7.

whom she fell

And knowing the height of the sun above the horizon allows you to determine the color temperature of daylight.

For each season and day, you can find the length of the shadow using a simple device - a pointer (indicator) of the shadow. A rod or a pin of a certain length is fixed on cardboard, for example, I cm. From the attachment point, as from the center, semicircles are applied (Fig. 8) with radii equal to 0.5-6 times the height of the protruding rod. When the cardboard is horizontal, the shadow from the rod will indicate the height of the sun.

(in Kyiv up to 63°). As the sun approaches the zenith, the light acquires a noticeable bluish tint, the color temperature rises to 6000-7000 K. This time (for Kyiv 11.00-13.00) is not suitable for photography and for artistic reasons.

The sun is an efficient source of infrared radiation. The illumination created by the infrared part of the sun's radiation depends on the position of the sun in the sky and the degree of transparency of the atmosphere. In table. Figure 6 shows in percent the radiation of the ultraviolet and infrared parts of the solar flux during the day for a transparent atmosphere. The radiation of the solar flux in the range from 3 to 70 is taken as 100%.

The table shows that with the rise of the sun, the intensity of infrared radiation noticeably weakens.

Incandescent lamps also belong to the group of temperature light sources. Simplicity and ease of use provided them with the greatest distribution in photography and filming. There are different types of electric incandescent lamps. These are household incandescent lighting lamps of different power, photo lamps, mirror lamps, in which part of the paraboloid-shaped bulb is covered with a mirror layer of aluminum, projector lamps (PZh), film projectors (KPZh), projection lamps. In recent years, halogen (iodine-quartz) lamps have been widely used.

In household lamps, the maximum radiation is in the infrared region of the spectrum, in the visible region, yellow-red rays predominate. As can be seen from the spectral characteristics (see Fig. 6), the radiation of an incandescent lamp in the red region of the spectrum exceeds the radiation in the blue-violet by 5-6 times. Therefore, the color rendering on black-and-white film under the light of incandescent lamps differs sharply from the color rendering in daylight.

At a nominal voltage of software, 127 and 220V, for low-power incandescent lamps (50-200 W), the color temperature of the light emitted by a tungsten filament is 2600-2800 K, for more powerful (500 and 1000 W) - about 3000 K, For even more powerful (over 1000 W) the color temperature exceeds 3000 K. Low-power household lamps with a low color temperature are not suitable for color photography.

SLR incandescent lamps (ZK) have a color temperature of 2800-3000K, for those intended for color shooting - 3200-3300 K. The color temperature of projector lamps (PL) ranges from 3000 K for lamps with a power of 500 W to 3200 K For lamps with a power of 5000-10,000 Tue Designed for color filming, KGShch and PZhK lamps have the same color temperature for all powers. As the temperature of the tungsten filament of the lamp increases, its color temperature increases.

Photo lamps intended for photography differ from ordinary ones in that they burn at increased voltage, with a large overheating. Due to this, not only the light intensity is significantly increased, but also the color temperature is increased. Compared to photo lamps, the light of household lamps is noticeably redder.

The constancy of the color temperature of incandescent lamps depends on the constancy of the voltage supplied to the lamp. Voltage fluctuations change the temperature of the tungsten filament and, consequently, the color temperature of the radiation.

When shooting on black and white film, the constancy of the color temperature of incandescent lamps is not as significant as on color. On a reversible color film, a deviation from the normal color temperature by 50-100K is already noticeable. Fluctuations in color temperature depending on the change in voltage are shown in fig. 9. Rated voltage is taken as 100%. For example, when the voltage is reduced to 90% of the nominal color temperature is reduced to 96% of the original. This reduction in voltage reduces the color temperature of the lamp from 3200 to 3072 K.

During combustion, as a result of spraying the filament, its surface decreases and a film forms on the inside of the flask. In the radiation of such a lamp there are always more red rays than in a new one of the same type.

Light - electromagnetic radiation emitted by a heated or excited substance, perceived by the human eye. Often, light is understood not only as visible light, but also as wide areas of the spectrum adjacent to it. One of the characteristics of light is its color, which for monochromatic radiation is determined by the wavelength, and for complex radiation - by its spectral composition.

Main the source of light is the sun. The light it emits is considered to be white. Light comes from the sun at different wavelengths.

Light has a temperature that depends on the power of light radiation. In turn, the power depends on the wavelength.

The light from an incandescent lamp appears white, but its spectrum is red-shifted.

The light from a fluorescent lamp is shifted towards the violet part of the spectrum, has a bluish color and a high color temperature.

The light of sunlight in the highlands is shifted towards violet waves. This is due to the rarefied atmosphere at high altitude.

In the sandy desert, the spectrum will be shifted towards the red waves, because. the radiation of hot sand is added to the sunlight.

When shooting, it is necessary to take into account these facts, to know the spectrum of the available light radiation in order to get a high-quality picture with the shades available in the original.

That. Photons of different lengths come from different light sources.

Color is the sensation evoked in the human eye and brain by light of varying wavelengths and intensities.

Radiation of different intensity objectively exists and causes the sensation of a certain color. But by itself it has no color. Color occurs in the organs of human vision. It does not exist independently of them. Therefore, it cannot be considered an objective value.

To describe color, subjective qualitative and quantitative assessments of its characteristics are used.

The causes of color sensations are electromagnetic radiation, light, the objective characteristics of which are associated with the subjective characteristics of color, its saturation, tone, brightness.

Color tone is subjective. due to the properties of human visual perception, light, intensity wave definition.

The temperature at which a black body emits light of the same spectral composition as the light under consideration is called the color temperature. It indicates only the spectral distribution of the radiation energy, and not the temperature of the source. Thus, the light of the blue sky corresponds to a color temperature of about 12,500-25,000 K, i.e., much higher than the temperature of the sun. Color temperature is expressed in Kelvin (K).

The concept of color temperature is applicable only to thermal (hot) light sources. The light of an electric discharge in gases and metal vapors (sodium, mercury, neon lamps) cannot be characterized by the value of the color temperature.

Remember: a sunny summer day - and suddenly a cloud appeared in the sky, it began to rain, which seemed to “not notice” that the sun continues to shine. Such rain is popularly called blind. The rain had not yet ended, and a multi-colored rainbow was already shining in the sky (Fig. 13.1). Why did she appear?

Breaking down sunlight into a spectrum.

Even in ancient times, it was noticed that the sunbeam, passing through a glass prism, becomes multi-colored. It was believed that the reason for this phenomenon is the property of a prism to color light. Is this really so, the outstanding English scientist Isaac Newton (1643-1727) found out in 1665 by conducting a series of experiments.

Rice. 13.1. A rainbow can be observed, for example, in the spray of a fountain or waterfall.

To get a narrow beam of sunlight, Newton made a small round hole in the shutter. When he installed a glass prism in front of the hole, a multi-colored strip appeared on the opposite wall, which the scientist called the spectrum. On the strip (as in the rainbow), Newton singled out seven colors: red, orange, yellow, green, blue, indigo, violet (Fig. 13.2, a).

Then, using a screen with a hole, the scientist singled out narrow single-color (monochromatic) beams of light from a wide multi-colored beam of rays and directed them again to the prism. Such beams were deflected by the prism, but were no longer decomposed into a spectrum (Fig. 13.2, b). In this case, the violet light beam was deflected more than others, and the red light beam was deflected less than others.

The results of the experiments allowed Newton to draw the following conclusions:

1) a beam of white (sunlight) light consists of light of different colors;

2) the prism does not “color” white light, but separates it (spreads it into a spectrum) due to the different refraction of light beams of different colors.

rice. 13.2. Scheme of I. Newton's experiments to determine the spectral composition of light

Compare fig. 13.1 and 13.2: the colors of the rainbow are the colors of the spectrum. And this is not surprising, because in fact the rainbow is a huge spectrum of sunlight. One of the reasons for the appearance of a rainbow is that many small water droplets refract the white sunlight.

Learn about the dispersion of light

Newton's experiments demonstrated, in particular, that when refracted in a glass prism, violet light beams always deviate more than red light beams. This means that for light beams of different colors, the refractive index of glass is different. That is why a beam of white light is decomposed into a spectrum.

The phenomenon of decomposition of light into a spectrum, due to the dependence of the refractive index of the medium on the color of the light beam, is called light dispersion.

For most transparent media, violet light has the highest refractive index, and red light has the lowest.

What color beam of light - violet or red - propagates in glass with greater speed? Hint: Remember how the refractive index of a medium depends on the speed of light in that medium.

We characterize colors

In the spectrum of sunlight, seven colors are traditionally distinguished, and more can be distinguished. But you will never be able to highlight, for example, brown or lilac. These colors are composite - they are formed as a result of superposition (mixing) of spectral (pure) colors in different proportions. Some spectral colors, when superimposed on each other, form white. Such pairs of spectral colors are called complementary (Fig. 13.3).

For human vision, the three main spectral colors - red, green and blue - are of particular importance: when superimposed, these colors give a wide variety of colors and shades.

The color image on the screens of a computer, TV, telephone is based on the superposition of the three primary spectral colors in different proportions (Fig. 13.4).

Rice. 13.5. Different bodies reflect, refract and absorb sunlight in different ways, and thanks to this we see the world around us in different colors.

Find out why the world is colorful

Knowing that white light is composite, it is possible to explain why the world around us, illuminated by only one source of white light - the Sun, we see as multi-colored (Fig. 13.5).

So, the surface of a sheet of office paper equally well reflects the rays of all colors, so a sheet illuminated with white light seems white to us. A blue backpack, illuminated by the same white light, predominantly reflects the blue rays, while absorbing the rest.

What color do you think most sunflower petals reflect? plant leaves?

Blue light directed at red rose petals will be almost completely absorbed by them, since the petals reflect predominantly red rays, while the rest absorb. Therefore, a rose illuminated with blue light will appear almost black to us. If white snow is illuminated with blue light, it will appear blue to us, because white snow reflects the rays of all colors (including blue). But the black fur of a cat absorbs all the rays well, so the cat will appear black when illuminated by any light (Fig. 13.6).

Note! Since the color of the body depends on the characteristics of the incident light, in the dark the concept of color is meaningless.

Rice. 13.6. The color of a body depends both on the optical properties of its surface and on the characteristics of the incident light.

Summing up

A beam of white light consists of light of different colors. There are seven spectral colors: red, orange, yellow, green, blue, indigo, violet.

The refractive index of light, and hence the speed of propagation of light in a medium, depends on the color of the light beam. if The dependence of the refractive index of the medium on the color of the light beam is called the dispersion of light. We see the world around us in different colors due to the fact that different bodies reflect, refract and absorb light in different ways.

test questions

1. Describe the experiments of I. Newton to determine the spectral composition of light.

2. Name seven spectral colors. 3. What color light beam is refracted in matter more than others? less than others? if 4. Define the dispersion of light. What natural phenomenon is associated with dispersion? 5. What colors are called complementary? 6. Name the three primary colors of the spectrum. Why are they called that? 7. Why do we see the world around us in different colors?

Exercise number 13

1. What will black letters on white paper look like when viewed through green glass? What will the color of the paper look like?

2. What colors of light pass through blue glass? absorbed by it?

3. Through what color glass can you not see text written in purple ink on white paper?

4. Light beams of red, orange and blue colors propagate in the water. Which beam propagates the fastest?

5. Use additional sources of information and find out why the sky is blue; Why is the sun often red at sunset?

Experimental task

"Rainbow Creators" Fill a shallow vessel with water and place it against a light wall. Place a flat mirror at an angle on the bottom of the vessel (see figure). Direct a beam of light at the mirror - a "sunbeam" will appear on the wall. Examine it and explain the observed phenomenon.

Physics and technology in Ukraine

Kyiv National University. Taras Shevchenko (KNU) was founded in November 1833 as the Imperial University of St. Vladimir. The first rector of the university is an outstanding scientist-encyclopedist Mikhail Aleksandrovich Maksimovich.

The names of well-known scientists — mathematicians, physicists, cybernetics, astronomers — are associated with KNU: D. A. Grave, M. F. Kravchuk, G. V. Pfeiffer, N. N. Bogolyubov, V. M. Glushkov, A. V. Skorokhod , I. I. Gikhman, B. V. Gnedenko, V. S. Mikhalevich, M. P. Avenarius, N. N. Schiller, I. I. Kosonogov, A. G. Sitenko, V. E. Lashkarev, R F. Vogel, M. F. Khandrikov, S. K. Vsekhsvyatsky.

Scientific schools of KNU are known in the world - algebraic, probability theory and mathematical statistics, mechanics, semiconductor physics, physical electronics and surface physics, metallogenic, optics of new materials, etc. Gubersky.

This is textbook material.