Applications and features of visible light and radiation. Visible radiation: application in medicine and in life, sources, properties, by whom and when discovered Visible wavelength range

Corresponds to some monochromatic radiation. Shades such as pink, beige or purple are formed only as a result of mixing several monochromatic radiations of different wavelengths.

Visible radiation also falls into 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 much more strongly than light with longer wavelengths (towards the red side of the spectrum), so the midday sky appears blue.

Many animal species are capable of seeing radiation that is not visible to the human eye, that is, not 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 more favorable position from the point of view of procreation if they are bright in the ultraviolet spectrum. Birds are also able to see ultraviolet radiation (300-400 nm), and some species even have markings on their plumage to attract a mate, visible only in ultraviolet light.

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✪ Infrared light: beyond the visible

✪ Visible radiation

✪ Birefringence (visible light)

✪ About the visible and the invisible

✪ Luminescence and phosphorescence

Subtitles

Humanity has always been drawn to the night sky. We drew pictures of the stars, followed the planets, We saw signs and predictions in celestial objects. When we look at the night sky, we see stars and planets, galaxies and nebulae only in visible light. How the Universe went from the first sparkling stars to the clusters of billions of stars that we see now.

Story

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

Newton was the first to use the word spectrum (Latin spectrum - vision, appearance) in print in 1671, describing his optical experiments. He discovered 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 multi-colored stripes. The scientist suggested that light consists of a stream of particles (corpuscles) of different colors, and that particles of different colors move in a transparent medium at different speeds. According to his assumption, red light moved faster than violet, and therefore the red beam was not deflected by the prism as much as the violet one. Because of this, a visible spectrum of colors arose.

Newton divided light into seven colors: red, orange, yellow, green, blue, indigo and violet. He chose the number seven from the belief (derived from the ancient Greek sophists) that there was a connection between colors, musical notes, objects in the solar system and days of the week. The human eye is relatively sensitive to indigo frequencies, so some people cannot distinguish it from blue or violet. Therefore, after Newton, it was often proposed that indigo should not be considered 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 the color blue.

Color	Wavelength range, nm	Frequency range, THz	Photon energy range, eV
Violet	≤450	≥667	≥2,75
Blue	450-480	625-667	2,58-2,75
Blue-green	480-510	588-625	2,43-2,58
Green	510-550	545-588	2,25-2,43
Yellow-green	550-570	526-545	2,17-2,25
Yellow	570-590	508-526	2,10-2,17
Orange	590-630	476-508	1,97-2,10
Red	≥630	≤476	≤1,97

The range boundaries indicated in the table are conditional; in reality, the colors smoothly transition into each other, and the location of the boundaries between them visible to the observer largely depends on the observation conditions.

Visible radiation is 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 these wavelengths is also called visible light, or simply light (in the narrow sense of the word). The human eye has the greatest sensitivity to light in the region of 555 nm (540 THz), in the green part of the spectrum.

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

Many animal species are capable of seeing radiation that is not visible to the human eye, that is, not 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 more favorable position from the point of view of procreation if they are bright in the ultraviolet spectrum. Birds are also able to see ultraviolet radiation (300-400 nm), and some species even have markings on their plumage to attract a mate, visible only in ultraviolet light.

The first explanations of the spectrum of visible radiation were given by Isaac Newton in his book “Optics” and Johann Goethe in his work “The 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 was the first to use the word spectrum (Latin spectrum - vision, appearance) in print in 1671, describing his optical experiments. He made the observation that when a ray 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 multi-colored stripes. 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 moved faster than violet, and therefore the red beam was not deflected by the prism as much as the violet one. Because of this, a visible spectrum of colors arose.

Newton divided light into seven colors: red, orange, yellow, green, blue, indigo and violet. He chose the number seven out of the belief (derived from the ancient Greek sophists) that there was a connection between colors, musical notes, objects in the solar system and days of the week. The human eye is relatively sensitive to indigo frequencies, so some people cannot distinguish it from blue or violet. Therefore, after Newton, it was often proposed that indigo should not be considered 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 the color blue.

Goethe, unlike Newton, believed that the spectrum arises from the superposition of different components of light. Observing wide beams of light, he discovered 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 a spectrum appears if these edges are brought close enough to each other.

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

In the early 19th century, Thomas Young and Hermann von Helmholtz also explored the relationship between the visible light spectrum and color vision. Their theory of color vision correctly suggested that it uses three different types of receptors to determine eye color.

Characteristics of visible radiation boundaries

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

Color	Wavelength range, nm	Frequency range, THz	Photon energy range, eV
Violet
Orange

The electromagnetic spectrum represents the range of all frequencies or wavelengths of electromagnetic radiation from very low energy frequencies such as radio waves to very high frequencies such as gamma rays. Light is the part of electromagnetic radiation that is visible to the human eye and is called visible light.

The sun's rays are much wider than the visible spectrum of light and are described as a full spectrum, including the range of wavelengths necessary to support life on earth: infrared, visible and ultraviolet (UV).

The human eye only responds to visible light, which lies between infrared and ultraviolet radiation and has tiny wavelengths. The wavelength of visible light is only 400 to 700 nm (nanometer-billionth of a meter).

The visible spectrum of light includes seven bands of color when the sun's rays are refracted through a prism: red, orange, yellow, green, cyan, indigo and violet.

The first person to discover that white is made up of the colors of the rainbow was Isaac Newton, who in 1666 directed a ray of sunlight through a narrow slit and then through a prism onto a wall - producing all visible colors.

Visible light application

Over the years, the lighting industry has rapidly developed electrical and artificial sources that mimic the properties of solar radiation.

In the 1960s, scientists coined the term "full spectrum lighting" to describe sources that emit a semblance of full natural light, which included the ultraviolet and visible spectrum needed for the health of humans, animals and plants.

Artificial lighting for a home or office involves natural lighting in a continuous spectral power distribution that represents the power of the source as a function of wavelength with a uniform level of radiant energy associated with and halogen lamps.

Visible light is part of electromagnetic radiation (EM), like radio waves, infrared radiation, ultraviolet radiation, X-rays and microwaves. Generally, visible light is defined as being visually detectable to most human eyes

EM radiation transmits waves or particles at different wavelengths and frequencies. So wide the range of wavelengths is called the electromagnetic spectrum.

The spectrum is generally divided into seven bands in order of decreasing wavelength and increasing energy and frequency. The general designation represents radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), x-rays, and gamma rays.

The wavelength of visible light lies in the range of the electromagnetic spectrum between infrared (IR) and ultraviolet (UV).

It has a frequency of 4 × 10 14 to 8 × 10 14 cycles per second, or hertz (Hz), and an oscillation length of 740 nanometers (nm) or 7.4 × 10 -5 cm to 380 nm or 3.8 × 10 - 5 cm.

What is color

Perhaps the most important characteristic of visible light is explanation of what color is. Color is an integral property and artifact of the human eye. Oddly enough, objects “do not have” color - it exists only in the head of the beholder. Our eyes contain specialized cells that form the retina, which acts as receivers tuned to wavelengths in this narrow frequency band.

Star Betelgeuse

Star Rigel

Astronomers can also tell which objects are made of what because each element absorbs light at specific wavelengths, called an absorption spectrum. Knowing the absorption spectra of elements, astronomers can use spectroscopes to determine the chemical composition of stars, gas and dust clouds and other distant objects.

Visible radiation is 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 these wavelengths is also called visible light, or simply light (in the narrow sense of the word). The human eye has the greatest sensitivity to light in the region of 555 nm (540 THz), in the green part of the spectrum.

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

Many animal species are capable of seeing radiation that is not visible to the human eye, that is, not 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 more favorable position from the point of view of procreation if they are bright in the ultraviolet spectrum. Birds are also able to see ultraviolet radiation (300-400 nm), and some species even have markings on their plumage to attract a mate, visible only in ultraviolet light.

The first explanations of the spectrum of visible radiation were given by Isaac Newton in his book “Optics” and Johann Goethe in his work “The 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 was the first to use the word spectrum (Latin spectrum - vision, appearance) in print in 1671, describing his optical experiments. He made the observation that when a ray 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 multi-colored stripes. 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 moved faster than violet, and therefore the red beam was not deflected by the prism as much as the violet one. Because of this, a visible spectrum of colors arose.

Newton divided light into seven colors: red, orange, yellow, green, blue, indigo and violet. He chose the number seven out of the belief (derived from the ancient Greek sophists) that there was a connection between colors, musical notes, objects in the solar system and days of the week. The human eye is relatively sensitive to indigo frequencies, so some people cannot distinguish it from blue or violet. Therefore, after Newton, it was often proposed that indigo should not be considered 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 the color blue.

Goethe, unlike Newton, believed that the spectrum arises from the superposition of different components of light. Observing wide beams of light, he discovered 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 a spectrum appears if these edges are brought close enough to each other.

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

In the early 19th century, Thomas Young and Hermann von Helmholtz also explored the relationship between the visible light spectrum and color vision. Their theory of color vision correctly suggested that it uses three different types of receptors to determine eye color.

Characteristics of visible radiation boundaries

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

Color	Wavelength range, nm	Frequency range, THz	Photon energy range, eV
Violet
Orange

The range of visible light is the narrowest in the entire spectrum. The wavelength in it changes less than twice. Visible light accounts for the maximum radiation in the solar spectrum. During evolution, our eyes have adapted to its light and are able to perceive radiation only in this narrow part of the spectrum. Almost all astronomical observations until the middle of the 20th century were carried out in visible light. The main source of visible light in space is stars, the surface of which is heated to several thousand degrees and therefore emits light. Non-thermal light sources are also used on Earth, such as fluorescent lamps and semiconductor LEDs.

Mirrors and lenses are used to collect light from faint cosmic sources. Receivers of visible light are the retina of the eye, photographic film, semiconductor crystals (CCD matrices) used in digital cameras, photocells and photomultipliers. The operating principle of the receivers is based on the fact that the energy of a visible light quantum is sufficient to provoke a chemical reaction in a specially selected substance or knock out a free electron from the substance. Then, based on the concentration of the reaction products or the amount of charge released, the amount of light received is determined.

Sources

One of the brightest comets of the late 20th century. It was discovered in 1995, when it was still beyond the orbit of Jupiter. This is a record distance for discovering a new comet. It passed perihelion on April 1, 1997, and at the end of May it reached its maximum brightness - about zero magnitude. In total, the comet remained visible to the naked eye for 18.5 months - double the previous record set by the great comet of 1811. The image shows two tails of the comet - dust and gas. The pressure of solar radiation directs them away from the Sun.

The second largest planet in the solar system. Belongs to the class of gas giants. The image was taken by the Cassini interplanetary station, which has been conducting research in the Saturn system since 2004. At the end of the 20th century, ring systems were discovered on all the giant planets - from Jupiter to Neptune, but only on Saturn they are easily observable even with a small amateur telescope.

Regions of low temperature on the visible surface of the Sun. Their temperature is 4300–4800 TO- about one and a half thousand degrees lower than on the rest of the surface of the Sun. Because of this, their brightness is 2–4 times lower, which by contrast creates the impression of black spots. Spots occur when a magnetic field slows down convection and thus the removal of heat in the upper layers of the Sun. They live from several hours to several months. The number of sunspots serves as an indicator of solar activity. Observing the sunspots over several days, it is easy to notice the rotation of the Sun. The picture was taken with an amateur telescope.

Attention! Under no circumstances should you look at the Sun through a telescope or other optical device without special protective filters. When using filters, they should be securely mounted in front of the lens, not at the instrument's eyepiece, where the filter could be damaged by overheating. In any case, it is safer to observe the projection of the image of the Sun onto a sheet of paper behind the telescope eyepiece.

Contains about 3 thousand stars, of which seven are visible to the naked eye. The cluster is 13 light-years across and located 400 light-years from Earth. Open clusters are formed when cosmic gas and dust clouds are compressed under the influence of self-gravity (the attraction of some parts of the cloud to others). During compression, the cloud is fragmented into parts, from which individual stars are formed. These stars are weakly bound together by gravity, and over time such clusters dissipate.

A spiral galaxy whose disk we see flat on, also known as the Whirlpool. Located at a distance of about 37 million light years. Its diameter is about 100 thousand light years. At the end of one of the spiral arms there is a companion galaxy.

The designation M51 refers to the entire pair as a whole. Individually, the main galaxy and its companion are designated NGC 5194 and 5195. Gravitational interaction with the companion compacts the gas in the spiral sections close to it, which accelerates star formation. Interaction is a typical phenomenon in the world of galaxies. The galaxy can be observed with a small amateur telescope.

Receivers

In professional astronomy, visual observations are no longer used. About 20 years ago they were completely replaced by digital photography, photometry, spectrometry and computer data processing.

However, the romance of visual observations still inspires astronomy enthusiasts. The Sun, Moon, five planets, about 6 thousand stars and four galaxies are visible to the naked eye - the Milky Way, the Andromeda Nebula, the Large and Small Magellanic clouds. Comets and asteroids visible to the eye occasionally appear.

Almost every night you can observe cosmic grains of sand - meteors - burning in the atmosphere, as well as artificial Earth satellites slowly crawling across the sky. At high latitudes, auroras are observed; at low latitudes, under favorable conditions, a ghostly zodiacal light is visible - cosmic dust illuminated by the Sun. And all this diversity is observed in an extremely narrow spectral range, which is almost a thousand times narrower than the infrared range.

Through binoculars, tens of times more stars and many nebulous objects are visible. An amateur telescope can see thousands of times more stars, details on the surfaces of planets, their satellites, as well as hundreds of nebulae and galaxies. But at the same time, the telescope’s field of view is much smaller, and for successful observations it must be securely fixed, or even better, slowly rotated following the rotation of the sky.

In the modern world, amateur astronomy has become a fascinating and prestigious hobby. A number of companies, such as Meade and Celestron, make telescopes specifically for hobbyists. The simplest instruments with a lens diameter of 50–70 mm cost 200–500 dollars, the largest with a diameter of 350–400 mm comparable in cost to a prestigious car and require permanent installation on a concrete foundation under a dome. In capable hands, such instruments may well contribute to greater science.

The most popular amateur telescopes in the world have a diameter of about 200 mm and are built according to an optical design invented by the Soviet optician Maksutov. They have a short tube, which is usually mounted on a fork mount and equipped with a computer to automatically point to various objects according to their celestial coordinates. This is exactly the tool shown on the poster.

In 1975, the 6-meter BTA telescope was built in the USSR. To prevent the telescope's main mirror from deforming, it was made about a meter thick. It seemed that it was impossible to further increase the size of the mirrors. However, a solution was found. Mirrors began to be made relatively thin (15–25 cm) and unload onto many supports, the position of which is controlled by a computer. The ability to bend mirrors, flexibly adjusting their shape, made it possible to build telescopes with a diameter of up to 8 meters.

But astronomers didn’t stop there. On the largest instruments, mirrors are divided into segments, aligning the positions of the parts with an accuracy of hundredths of a micron. This is how the world's largest 10-meter Keck telescopes are designed. The next step will be the American Magellan telescope, which will have 7 mirrors, each with a diameter of 8 meters. Together they will operate as a 24-meter telescope. And in the European Union, work has begun on an even more ambitious project - a telescope with a diameter of 42 meters.

The main obstacle to realizing the capabilities of such instruments is the earth's atmosphere, the turbulence of which distorts the image. To compensate for interference, special equipment constantly monitors the state of the atmosphere and bends the telescope mirror as it goes so as to compensate for distortions. This technology is called adaptive optics.

A telescope performs two tasks: to collect as much light as possible from a weak source and to discern as small details as possible. The light-gathering ability of a telescope is determined by the area of ​​the main mirror, and the resolution by its diameter. That is why astronomers strive to build telescopes as large as possible.

For small telescopes, a collecting lens (refractor telescope) can be used as a lens, but a concave parabolic mirror (reflector telescope) is more often used. The main function of the lens is to construct an image of the observed sources in the focal plane of the telescope, where the camera or other equipment is located. In amateur telescopes, for visual observations, an eyepiece is placed behind the focal plane, which is essentially a strong magnifying glass through which the image created by the lens is viewed.

However, the focal plane of a reflector is located in front of the mirror, which is not always convenient for observations. Various techniques are used to bring a beam of light outside the telescope tube. Newton's system uses a diagonal mirror for this. In a more complex Cassegrain system (on the poster), a secondary convex mirror in the shape of a hyperboloid of revolution is placed opposite the main mirror. It reflects the beam back, where it exits through a hole in the center of the primary mirror. In the Maksutov system, a thin convex-concave lens is placed at the front end of the telescope tube. It not only protects the telescope mirrors from damage, but also allows you to make the main mirror not parabolic, but spherical, which is much cheaper to manufacture.

The largest orbital optical telescope. The diameter of its main mirror is 2.4 meters. Launched into orbit in 1991. It can conduct observations in the visible, near-infrared and near-ultraviolet ranges. The only space telescope visited by astronauts for repairs and maintenance.

Astronomy owes dozens of discoveries to the Hubble Telescope. Among other things, it made it possible to see what galaxies looked like at the time of their birth about 13 billion years ago. Currently, a new generation space telescope is being created to replace the Hubble telescope - the James Webb Space Telescope (JWST) with a diameter of 6.5 meters, which is planned to be launched into space in 2013. True, it will not work in the visible range, but in the near and mid-infrared.

Sky Reviews

Here again the plane of our Galaxy - the Milky Way - is clearly visible. Its glow is made up of the light of hundreds of billions of stars and nebulae. Also clearly visible are the dark filaments of dust clouds, which obscure some of the light from stars in the galactic plane from us.

The nebulous formations in the lower half of the view are the Large and Small Magellanic Clouds, satellites of our Galaxy. Bright stars, which seem to us to be the main objects in the sky, are practically invisible on such a small-scale map.

Sky in the line of hydrogen H-alpha, 656 nm

The H-alpha spectral line corresponds to the transition of an electron in a hydrogen atom from the third energy level to the second.

This is the first line of the so-called Balmer series, which all consists of transitions from various higher levels to the second. There are similar series of transitions to the first level (Lyman series), to the third level (Paschen series) and to other levels. A distinctive feature of the Balmer series is that it is located almost entirely in the visible range, which greatly facilitates observations. In particular, the H-alpha line falls in the red part of the spectrum.

Radiation in this line arises in rarefied cosmic clouds of atomic hydrogen. The atoms in them are excited by ultraviolet radiation from hot stars, and then give off energy, moving to lower levels. By isolating the H-alpha line using filters, it is possible to specifically observe the distribution of neutral hydrogen.

An H-alpha sky survey shows the distribution of gas in our Galaxy. It shows large gas bubbles around regions of active star formation.

Terrestrial Application

When viewing objects at a distance of clear vision (25 cm) a person can distinguish details with a size of about 0.1 mm(angular resolution of the eye is about one arc minute 1" = 2.3 × 10 -4 rad). To see finer details, you need to look from a shorter distance, but at a distance less than 10 cm It is very difficult for the eye to tune in.

This can be achieved by using a magnifying glass, the optical power of which is added to the optical power of the lens. But even in this case, the magnification limit is approximately 25x, since the size of such a strong magnifying glass becomes very small and it has to be placed close to the sample. In fact, such a magnifying glass becomes a microscope lens. It is very uncomfortable to look into it with your eyes, but you can do otherwise.

By carefully adjusting the distance from the lens to the object, you can get an enlarged image of it at some distance behind the lens. By placing another magnifying glass behind it and viewing the image created by the lens through it, you can achieve a magnification of hundreds or even more than a thousand times.

However, magnifications noticeably more than 1000 times have no practical meaning, since the wave nature of light does not allow us to examine details smaller than the wavelength (400–700 nm). At 2000x magnification, such details are visible as millimeter divisions on a ruler you hold in your hands.

Increasing the magnification further will not reveal new details to you. To see details with greater resolution, X-rays with a shorter wavelength are required, or even streams of electrons, which (according to quantum mechanics) have a shorter wavelength. You can also use a mechanical probe with a very precise aiming system - the so-called scanning microscope.