Visible light is the energy of that part of the spectrum of electromagnetic radiation that we are able to perceive with our eyes, that is, to see. It's that simple.

Visible light wavelength

And now it's harder. The wavelengths of light in the visible region of the spectrum lie in the range from 380 to 780 nm. What does it mean? This means that these waves are very short and high-frequency, and "nm" is a nanometer. One such nanometer is equal to 10 -9 meters. And if human language, then it is one billionth of a meter. That is, a meter is ten decimeters, one hundred centimeters, a thousand millimeters, or ... Attention! One billion nanometers.

How do we see colors in the visible light spectrum?

Not only can our eyes perceive these tiny waves, but they can also distinguish their wavelengths within the spectrum. This is how we see color as part of the visible spectrum of light. Red light, one of the three primary colors of light, has a wavelength of approximately 650 nm. Green (second primary) - approximately 510 nm. And finally, the third - blue - 475 nm (or so). Visible light from the Sun is a kind of cocktail in which these three colors are mixed.

Why is the sky blue and the grass green?

In fact, these are two questions, not one. And so we will give two different, but related answers. We see clear skies blue at noon because short wavelengths of light scatter more efficiently when they collide with gas molecules in the atmosphere than long wavelengths do. So the blueness that we see in the sky is blue light scattered and repeatedly reflected by the molecules of the atmosphere.

But at sunrise and sunset, the sky can take on a reddish color. Yes, it happens, trust me. This is because when the Sun is close to the horizon, light has to travel a longer distance through a much denser (and rather dusty) atmosphere to reach us than when the Sun is at its zenith. All short waves are absorbed, and we have to be content with long ones, which are responsible for the red part of the spectrum.

But with grass, things are a little different. It looks green because it absorbs all wavelengths except green. She doesn't like green, you see, so she reflects them back into our eyes. For the same reason, any object has its own color - we see that part of the light spectrum that it could not absorb. Black objects look black because they absorb all wavelengths, while reflecting almost nothing, while white objects, on the contrary, reflect the entire visible spectrum of light. This also explains why black heats up much more in the sun than white.

The sky is blue, the grass is green, the dog is man's best friend

And what is there - beyond the visible region of the spectrum?

As the waves get shorter, the color changes from red to blue to purple and finally visible light disappears. But the light itself did not disappear - but moved into the region of the spectrum, which is called ultraviolet. Although we no longer perceive this part of the light spectrum, it is it that makes fluorescent lamps, some types of LEDs, as well as all sorts of cool things that glow in the dark, glow in the dark. Next comes X-ray and gamma radiation, with which it is better not to deal with at all.

At the other end of the visible light spectrum, where red ends, infrared radiation begins, which is more heat than light. It might well fry you. Then comes microwave radiation (very dangerous for eggs), and even further - what we used to call radio waves. Their lengths are already measured in centimeters, meters and even kilometers.

And what does all this have to do with lighting?

Very pertinent! Since we have learned a lot about the visible light spectrum and how we perceive it, lighting equipment manufacturers have been constantly working to improve quality to meet our ever-growing needs. This is how “full spectrum” lamps appeared, the light of which is almost indistinguishable from natural. Light steel color to have real numbers for comparison and marketing gimmicks. Special lamps for various needs began to be produced: for example, lamps for growing indoor plants, giving more ultraviolet and light from the red region of the spectrum for better growth and flowering, or "heat lamps" various kinds, which settled in household heaters, toasters, and a grill in Ashot's Shawarma.

Every movement, every action surrounding us space is a manifestation of energy. In its eternal change, energy takes on various forms, which we call mechanical, thermal, chemical, electrical energy. One form of energy is known as radiant energy. Radiant energy is emitted by any incandescent body, including the sun. Any body that emits light, that is, glows, is called a source of light. The most common cause of glow is high temperature.

The higher the temperature, the brighter light emitted by the body. When a piece of iron is heated to 500°C, it remains a dark, nonluminous body. With its further heating above 600-700 °, a piece of iron becomes dark red, emitting light. At 800-1000° iron already glows with light red light, at a temperature of 1000-1200° yellow, and at a temperature of about 1500° a piece of iron begins to radiate yellowish light. White light. Refractory bodies, heated to 2000-2500 °, already emit dazzling white light - a stream of various light rays, which are electromagnetic oscillations of various wavelengths (oscillation frequencies).

permanent source of radiant energy is the sun. Theoretical calculations force us to assume that at the center of the sun the temperature is 20,000,000° under enormous pressure. All space around the sun is filled with a stream of light energy. This flow of solar energy at a speed of 300,000 km / s spreads in all directions from the center.

From a continuous stream only one two-billionth of the solar energy reaches our planet. Some of this energy is reflected from the atmosphere the globe and is scattered by the atmosphere in all directions, part goes to heat the air and up to earth's surface reaches less than half.

With light treatment and hardening various sources are used: natural - the sun (heliotherapy) and all kinds of artificial - mercury-quartz lamps, lighting devices, etc. (phototherapy).

light spectrum

light beam, passed through a prism, decomposes into a series of colored bands. Newton called the color bands obtained on the screen after decomposition of the beam a spectrum. Colored stripes gradually turn into one another. Visible part The spectrum covers rays with a wavelength from 760 mu (red) to 400 tu (violet).

Wavelength from the red beam to the violet gradually decreases, and the frequency of oscillations, on the contrary, increases. This entire group of rays is called light, or visible.

Infrared and ultraviolet rays located on both sides of the visible rays: behind the red - infrared, behind the violet - ultraviolet. They are called invisible because they are not perceived by the retina.

infrared rays- the longest - from 760 tu to 0.3 mm. To the left of the infrared part of the spectrum (from 0.3 mm to 3 mm long) lie radio beams having a longer wavelength. Ultraviolet rays are shorter - from 400 to 180 mu. Beyond the ultraviolet part of the spectrum are X-rays, gamma rays, and even further cosmic rays.

When studying rays with different wavelengths, it was experimentally established that the rays of the left part of the spectrum, i.e. infrared, red and orange, have a large thermal effect; the rays of the middle part of the spectrum, i.e., yellow and green, act mainly optically, while blue, violet and ultraviolet (on the right side of the spectrum) have a predominantly chemical effect.

Usually everything types of radiant energy they have the ability and TC to thermal and chemical action, the same in quality, but different in quantity, therefore it is wrong to call red and infrared rays thermal, and blue, violet and ultraviolet - chemical, and dividing the spectrum into thermal, light and chemical rays would be wrong.

In most cases, rays falling on various bodies are absorbed by them and converted into heat. The amount of heat thus obtained will be directly proportional to the energy of the absorbed rays.

Corresponds to some kind of monochromatic radiation. Hues such as pink, beige or purple are only produced by mixing several monochromatic radiations with different wavelengths.

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

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

Encyclopedic YouTube

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✪ Infrared light: beyond the visible

✪ Visible radiation

✪ double refraction(visible light)

✪ About visible and invisible

✪ Luminescence and phosphorescence

Subtitles

Mankind has always been drawn to the night sky We drew pictures from the stars, followed the planets, We saw signs and predictions in celestial objects. But there is still so much unknown in the universe. Huge distances separate us from the objects that would help us find answers to the most important questions: How did galaxies form? How did the stars and planets appear? Are there conditions on other planets suitable for life? In order to develop and test our theories, we need to know what is going on in space. Therefore, we create devices that help us see more. They are getting bigger and bigger. Everything is more powerful. Everything is more perfect. Over time, astronomers stopped relying only on light visible to the naked eye. When you look at the world around you, you see the so-called "visible light". But visible light is only one form of radiation. There are many different types of radiation in the universe. It is everywhere. Our body has learned to perceive visible light through the eyes. But it has also learned to sense another kind of radiation called infrared light. Our body feels it as heat. This infrared radiation was discovered by the astronomer Frederick William Herschel. Herschel knew that a prism could be used to separate white light into different colors. He wanted to know if different colors have different temperatures. And it turned out that they have! But then Herschel measured the temperature of the empty space next to the red. No light was visible, but the temperature rose. So Herschel discovered invisible infrared radiation. Now mankind knows that there are types of radiation invisible to the eye. They can be anywhere. All around us. How many are there? Why do they exist? What are they hiding? Of course we had to find out. The energy that travels through the universe in the form of waves is called electromagnetic radiation. The whole range of studies: from gamma rays to high energy to low energy radio waves is called the electromagnetic spectrum. Our eyes only see visible light, but we can build devices like infrared cameras to see other types of light as well. These man-made "eyes" see the invisible light for us and turn it into a picture that is understandable to our eyes. Objects can emit different types of radiation. By observing the full spectrum of an item, we can see the true picture of the item. When we point such devices into the sky, they reveal the cosmos to us in all its glory. When we look at the night sky, we see stars and planets, galaxies and nebulae only in visible light. But if infrared light could be discerned, the sky would look completely different. First, long wavelengths of infrared light can pass through clouds of gas and dust. The shorter wavelengths of visible light are blocked, or scattered, as they pass through such particle clusters. It turns out that by observing infrared light, we can see objects that emit heat even through clouds of gas and dust. Like this newly formed star. Objects that don't emit visible light on their own, like planets, can be hot enough to emit infrared light, allowing us to see them. And by watching the infrared light of a star pass through the atmosphere, we can study the chemical composition of the planet. The dust tail left by distant planets during their formation also emits infrared light, helping us understand how new planets are born. So, infrared light helps us to see objects that are nearby. But besides this, he can tell us about how the very first objects in the Universe appeared immediately after big bang. Imagine that you are sending a letter to Earth from a galaxy billions of light-years away. It will take an incredibly long time! And when it finally arrives, whoever reads it will find out news that is billions of years old. The light of the very first stars formed in the young Universe behaves in exactly the same way. He leaves the stars many years ago and travels through space, overcoming gigantic distances between galaxies. If we could see him, we would see galaxies like this as they were in the early universe. It turns out we could see the past! But, unfortunately, we cannot see it. Why? Because the universe is expanding. As light travels through space, it is stretched out by this expansion. The first stars shone mainly in the visible and ultraviolet spectra, but stretching changed the wavelength of the light, turning it into infrared. This effect is called "redshift". The only way to see the light from distant stars reaching us is to look for very dim infrared light. By collecting it, we can recreate images of the very first galaxies that appeared in the universe. Watching the birth of the first stars and galaxies, we deepen our knowledge of how our universe was formed. How the Universe went from the first sparkling stars to the billions of stars we see today. What do we learn about how galaxies grew and evolved? How did the chaos of the early universe acquire order and structure? NASA is currently building the new James Webb Space Telescope. With a huge infrared-collecting mirror and an orbit far behind the moon, Webb will allow us to see the cosmos like we've never seen it before. Webb will look for signs of water on planets orbiting other stars. Will take photographs of the infancy of our universe. He will see stars and planetary systems hidden in cocoons of dust. Will be able to find answers to the most important questions of the Universe, and perhaps even to those that we have not yet had time to ask. The answers that hide from us in the form of infrared light. All we have to do is look. [Infrared Light: Beyond the Visible] [How the James Webb Telescope Works] Translation and subtitles: astronomyday.ru

Story

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

Newton was the first to use the word spectrum (lat. 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 bands of different colors. The scientist suggested that light consists of a stream of particles (corpuscles) of different colors, and that particles of different colors move in a transparent medium at different speeds. According to his assumption, red light traveled faster than violet, and therefore the red beam was not deflected on the prism as much as violet. Because of this, a visible spectrum of colors arose.

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

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 boundaries of the ranges indicated in the table are conditional, but in reality the colors smoothly transition into each other, and the location of the boundaries between them visible to the observer depends to a large extent on the conditions of observation.

The electromagnetic spectrum is conditionally divided into ranges. As a result of their consideration, you need to know the following.

• The name of the ranges of electromagnetic waves.
• The order in which they follow.
• Range boundaries in wavelengths or frequencies.
• What causes the absorption or emission of waves of one or another range.
• The use of each type of electromagnetic waves.
• Sources of radiation of various electromagnetic waves (natural and artificial).
• Danger of every kind of waves.
• Examples of objects that have dimensions comparable to the wavelength of the corresponding range.
• The concept of black body radiation.
• Solar radiation and atmospheric transparency windows.

Ranges of electromagnetic waves

microwave range

Microwave radiation is used to heat food in microwave ovens, mobile communications, radars (radar), up to 300 GHz easily passes through the atmosphere, therefore it is suitable for satellite communications. Radiometers for remote sensing and determining the temperature of different layers of the atmosphere, as well as radio telescopes, operate in this range. This range is one of the key ones for EPR spectroscopy and rotational spectra of molecules. Prolonged exposure to the eyes causes cataracts. Cell phones negatively affect the brain.

A characteristic feature of microwave waves is that their wavelength is comparable to the size of the equipment. Therefore, in this range, devices are designed on the basis of distributed elements. Waveguides and strip lines are used for energy transmission, and cavity resonators or resonant lines are used as resonant elements. Man-made sources of MW waves are klystrons, magnetrons, traveling wave tubes (TWTs), Gunn diodes, and avalanche transit diodes (ATDs). In addition, there are masers, analogues of lasers in the long wavelength ranges.

Microwave waves are emitted by stars.

In the microwave range is the so-called cosmic background microwave radiation (cosmic background radiation), which, by its spectral characteristics fully corresponds to the radiation of a completely black body with a temperature of 2.72K. The maximum of its intensity falls at a frequency of 160 GHz (1.9 mm) (see figure below). The presence of this radiation and its parameters are one of the arguments in favor of the Big Bang theory, which is currently the basis of modern cosmology. The last one, according to these measurements and observations in particular, occurred 13.6 billion years ago.

Above 300 GHz (shorter than 1 mm), electromagnetic waves are very strongly absorbed by the Earth's atmosphere. The atmosphere begins to be transparent in the IR and visible ranges.

Color	Wavelength range, nm	Frequency range, THz	Photon energy range, eV
Violet	380-440	680-790	2,82-3,26
Blue	440-485	620-680	2,56-2,82
Blue	485-500	600-620	2,48-2,56
Green	500-565	530-600	2,19-2,48
Yellow	565-590	510-530	2,10-2,19
Orange	590-625	480-510	1,98-2,10
Red	625-740	400-480	1,68-1,98

Among the lasers and sources with their application, emitting in the visible range, the following can be mentioned: the first launched laser, - ruby, with a wavelength of 694.3 nm, diode lasers, for example, based on GaInP and AlGaInP for the red range, and based on GaN for the blue range, titanium-sapphire laser, He-Ne laser, argon and krypton ion lasers, copper vapor laser, dye lasers, lasers with frequency doubling or frequency summation in nonlinear media, Raman lasers. (https://www.rp-photonics.com/visible_lasers.html?s=ak).

For a long time there was a problem in creating compact lasers in the blue-green part of the spectrum. There were gas lasers, such as the argon ion laser (since 1964), which has two main generation lines in the blue and green parts of the spectrum (488 and 514 nm), or the helium-cadmium laser. However, they were not suitable for many applications due to their bulkiness and the limited number of generation lines. It was not possible to create semiconductor lasers with a wide bandgap due to enormous technological difficulties. However, eventually developed effective methods doubling and tripling the frequency of solid-state lasers in the IR and optical range in nonlinear crystals, semiconductor lasers based on double GaN compounds and lasers with an increase in the pump frequency (upconversion lasers).

Light sources in the blue-green area allow you to increase the recording density on CD-ROM, the quality of reprographics, are necessary for creating full-color projectors, for communicating with submarines, for taking relief seabed, for laser cooling of individual atoms and ions, for monitoring vapor deposition, in flow cytometry. (taken from “Compact blue-green lasers” by W. P. Risk et al).

Literature:

UV range

It is believed that the ultraviolet range occupies the region from 10 to 380 nm. Although its boundaries are not clearly defined, especially in the shortwave region. It is divided into sub-ranges and this division is also not unambiguous, since in different sources it is tied to various physical and biological processes.

So on the website of the "Health Physics Society" the ultraviolet range is defined within the limits of 40 - 400 nm and is divided into five subranges: vacuum UV (40-190 nm), far UV (190-220 nm), UVC (220-290 nm), UVB (290-320 nm), and UVA (320-400 nm) (black light). In the English version of the Wikipedia article on ultraviolet "Ultraviolet", the range of 40 - 400 nm is allocated to ultraviolet radiation, however, in the table in the text it is divided into a bunch of overlapping subranges, starting from 10 nm. In the Russian-language version of Wikipedia "Ultraviolet radiation" from the very beginning, the limits of the UV range are set within 10 - 400 nm. In addition, Wikipedia for the UVC, UVB and UVA ranges indicates the areas 100 - 280, 280 - 315, 315 - 400 nm.

Ultraviolet radiation, despite its beneficial effect in small quantities on biological objects, is at the same time the most dangerous of all other natural widespread radiations of other ranges.

The main natural source of UV radiation is the Sun. However, not all radiation reaches the Earth, as it is absorbed ozone layer stratosphere and in the region shorter than 200 nm is very strongly atmospheric oxygen.

UVC is almost completely absorbed by the atmosphere and does not reach the earth's surface. This range is used by germicidal lamps. Overexposure results in corneal damage and snow blindness, as well as severe facial burns.

UVB is the most damaging part of UV radiation as it has enough energy to damage DNA. It is not completely absorbed by the atmosphere (about 2% passes). This radiation is necessary for the production (synthesis) of vitamin D, but the harmful effects can cause burns, cataracts and skin cancer. This part of the radiation is absorbed by atmospheric ozone, the decline of which is a cause for concern.

UVA almost completely reaches the Earth (99%). It is responsible for sunburn, but excess leads to burns. Like UVB, it is necessary for the synthesis of vitamin D. Excessive exposure leads to suppression immune system, skin stiffness and cataract formation. Radiation in this range is also called black light. Insects and birds are able to see this light.

The figure below shows, for example, the dependence of ozone concentration on height at northern latitudes (yellow curve) and the level of blocking of solar ultraviolet by ozone. UVC is completely absorbed up to altitudes of 35 km. At the same time, UVA almost completely reaches the Earth's surface, but this radiation poses practically no danger. Ozone traps most of the UVB, but some reaches the Earth. In the event of depletion of the ozone layer, most of it will irradiate the surface and lead to genetic damage to living beings.

Brief list of uses of electromagnetic waves in the UV range.

• High quality photolithography for the manufacture of electronic devices such as microprocessors and memory chips.
• In the manufacture of fiber optic elements, in particular Bragg gratings.
• Disinfection from microbes of products, water, air, objects (UVC).
• Black light (UVA) in forensics, in the examination of works of art, in the establishment of the authenticity of banknotes (fluorescence phenomenon).
• Artificial tan.
• Laser engraving.
• Dermatology.
• Dentistry (photopolymerization of fillings).

Man-made sources of ultraviolet radiation are:

Non-monochromatic: Mercury discharge lamps of various pressures and designs.

Monochromatic:

1. Laser diodes, mainly based on GaN, (low power), generating in the near ultraviolet range;
2. Excimer lasers are very powerful sources of ultraviolet radiation. They emit nanosecond (picosecond and microsecond) pulses with an average power ranging from a few watts to hundreds of watts. Typical wavelengths lie between 157 nm (F2) to 351 nm (XeF);
3. Some solid-state lasers doped with cerium, such as Ce3+:LiCAF or Ce3+:LiLuF4, which are pulsed with nanosecond pulses;
4. Some fiber lasers, such as those doped with neodymium;
5. Some dye lasers are capable of emitting ultraviolet light;
6. Ion argon laser, which, despite the fact that the main lines lie in the optical range, can generate continuous radiation with wavelengths of 334 and 351 nm, but with lower power;
7. Nitrogen laser emitting at a wavelength of 337 nm. A very simple and cheap laser, operates in a pulsed mode with a nanosecond pulse duration and with a peak power of several megawatts;
8. Triple frequencies of Nd:YAG laser in nonlinear crystals;

Literature:

1. Wikipedia "Ultraviolet".

We often talk about such a concept as light, light sources, the color of images and objects, but we don’t quite understand what light is and what color is. It is time to deal with these issues and move from representation to understanding.

We are surrounded

Whether we realize it or not, we are in constant interaction with the outside world and take on the impact various factors of this world. We see the space around us, we constantly hear sounds from various sources, we feel heat and cold, we do not notice that we are under the influence of natural background radiation, and we are constantly in the radiation zone that comes from a huge number of sources of telemetry, radio and telecommunication signals. Almost everything around us emits electromagnetic radiation. Electromagnetic radiation is electromagnetic waves created by various radiating objects - charged particles, atoms, molecules. Waves are characterized by repetition frequency, length, intensity, and a number of other characteristics. Here is just an introductory example. The heat emanating from a burning fire is an electromagnetic wave, or rather infrared radiation, and of very high intensity, we do not see it, but we can feel it. The doctors took an x-ray - irradiated with electromagnetic waves with a high penetrating power, but we did not feel and did not see these waves. What electricity and all devices that operate under its influence are sources of electromagnetic radiation, of course, you all know. But in this article I will not tell you the theory of electromagnetic radiation and its physical nature I will try more than me plain language explain what visible light is and how the color of objects that we see is formed. I started talking about electromagnetic waves to tell you the most important thing: Light is an electromagnetic wave that is emitted by a heated or excited state of matter. The role of such a substance can be played by the sun, an incandescent lamp, an LED flashlight, a fire flame, various kinds of chemical reactions. There can be quite a lot of examples, you yourself can bring them to much more than I wrote. It should be clarified that by the term light we mean visible light. All of the above can be represented in the form of such a picture (Figure 1).

Figure 1 - The place of visible radiation among other types of electromagnetic radiation.

Figure 1 visible radiation presented in the form of a scale, which consists of a "mixture" of different colors. As you may have guessed, this range. A wavy line (sinusoidal curve) passes through the entire spectrum (from left to right) - this is an electromagnetic wave that reflects the essence of light as electromagnetic radiation. Roughly speaking, any radiation is a wave. X-ray, ionizing, radio emission (radio receivers, television communications) - it does not matter, they are all electromagnetic waves, only each type of radiation has a different wavelength of these waves. A sinusoidal curve is just a graphical representation of radiated energy that changes over time. This is a mathematical description of the radiated energy. In figure 1, you can also notice that the depicted wave seems to be slightly compressed in the left corner and expanded in the right. This suggests that it has a different length in different areas. The wavelength is the distance between its two adjacent peaks. Visible radiation (visible light) has a wavelength that varies from 380 to 780nm (nanometers). Visible light is just a link of one very long electromagnetic wave.

From light to color and back

You know from school that if you put a glass prism in the path of a ray of sunlight, then most of the light will pass through the glass, and you can see the multi-colored stripes on the other side of the prism. That is, initially there was sunlight - a beam of white color, and after passing through a prism it was divided into 7 new colors. This suggests that white light is made up of these seven colors. Remember, I just said that visible light (visible radiation) is an electromagnetic wave, and so, those multi-colored stripes that turned out after passing sunbeam through a prism - there are separate electromagnetic waves. That is, 7 new electromagnetic waves are obtained. Look at figure 2.

Figure 2 - The passage of a beam of sunlight through a prism.

Each wave has its own length. You see, the peaks of neighboring waves do not coincide with each other: because the red color (red wave) has a length of about 625-740nm, the orange color (orange wave) has a length of about 590-625nm, the blue color (blue wave) has a length of 435-500nm., I will not give figures for the remaining 4 waves, I think you understand the essence. Each wave is an emitted light energy, i.e. a red wave emits red light, an orange wave emits orange, a green wave emits green, and so on. When all seven waves are emitted at the same time, we see a spectrum of colors. If we mathematically add the graphs of these waves together, then we get the original graph of the electromagnetic wave of visible light - we get white light. Thus, it can be said that range visible light electromagnetic wave sum waves of different lengths, which, when superimposed on each other, give the original electromagnetic wave. The spectrum "shows what the wave consists of." Well, to put it quite simply, the spectrum of visible light is a mixture of colors that make up white light (color). I must say that other types of electromagnetic radiation (ionizing, X-ray, infrared, ultraviolet, etc.) also have their own spectra.

Any radiation can be represented as a spectrum, though there will be no such colored lines in its composition, because a person is not able to see other types of radiation. Visible radiation is the only type of radiation that a person can see, which is why this radiation is called visible. However, the energy of a certain wavelength does not have any color by itself. Human perception of electromagnetic radiation in the visible range of the spectrum occurs due to the fact that in the human retina there are receptors that can respond to this radiation.

But is it only by adding the seven primary colors that we can get white? Not at all. As a result scientific research and practical experiments, it has been found that all the colors that the human eye can perceive can be obtained by mixing just three primary colors. Three primary colors: red, green, blue. If by mixing these three colors you can get almost any color, then you can get white! Look at the spectrum that was shown in Figure 2, three colors are clearly visible on the spectrum: red, green and blue. It is these colors that underlie the RGB (Red Green Blue) color model.

Let's check how it works in practice. Let's take 3 light sources (spotlights) - red, green and blue. Each of these spotlights emits only one electromagnetic wave of a certain length. Red - corresponds to the radiation of an electromagnetic wave with a length of approximately 625-740nm (the beam spectrum consists only of red), blue emits a wave of 435-500nm (the beam spectrum consists of only blue), green - 500-565nm (in the beam spectrum only green color). Three different waves and nothing else, there is no multi-colored spectrum and additional colors. Now let's direct the spotlights so that their beams partially overlap each other, as shown in Figure 3.

Figure 3 - The result of overlaying red, green and blue colors.

Look, at the places where the light rays intersect with each other, new light rays have formed - new colors. Green and red formed yellow, green and blue - cyan, blue and red - magenta. Thus, by changing the brightness of the light rays and combining colors, you can get a wide variety of color tones and shades of color. Pay attention to the center of the intersection of green, red and blue: in the center you will see white. The one we talked about recently. White color is the sum of all colors. It is the "strongest color" of all the colors we see. The opposite of white is black. Black color is the complete absence of light at all. That is, where there is no light - there is darkness, everything becomes black there. An example of this is Figure 4.

Figure 4 - Lack of light emission

I somehow imperceptibly move from the concept of light to the concept of color and I don’t tell you anything. It's time to be clear. We have found out that light- this is the radiation that is emitted by a heated body or a substance in an excited state. The main parameters of the light source are the wavelength and light intensity. Color- This quality characteristic this radiation, which is determined on the basis of the resulting visual sensation. Of course, the perception of color depends on the person, his physical and psychological condition. But let's assume that you are feeling well enough, reading this article and you can distinguish the 7 colors of the rainbow from each other. I note that at the moment, we are talking about the color of light radiation, and not about the color of objects. Figure 5 shows color and light parameters that are dependent on each other.

Figures 5 and 6 - Dependence of color parameters on the source of radiation

There are basic color characteristics: hue, brightness (Brightness), lightness (Lightness), saturation (Saturation).

Color tone (hue)

- This is the main characteristic of a color that determines its position in the spectrum. Remember our 7 colors of the rainbow - in other words, 7 color tones. Red color tone, orange color tone, green color tone, blue, etc. There can be quite a lot of color tones, I gave 7 colors of the rainbow just as an example. It should be noted that such colors as gray, white, black, as well as shades of these colors do not belong to the concept of color tone, as they are the result of mixing different color tones.

Brightness

- A feature that shows how strong light energy of one or another color tone (red, yellow, violet, etc.) is emitted. What if it doesn't radiate at all? If it does not radiate, it means that it is not there, but there is no energy - there is no light, and where there is no light, there is black color. Any color at the maximum decrease in brightness becomes black. For example, a chain of reducing the brightness of red: red - scarlet - burgundy - brown - black. The maximum increase in brightness, for example, the same red color will give "maximum red color".

Lightness

– The degree of proximity of a color (hue) to white. Any color at the maximum increase in lightness becomes white. For example: red - crimson - pink - pale pink - white.

Saturation

– The degree of closeness of a color to gray. Gray is an intermediate color between white and black. The gray color is formed by mixing in equal amounts of red, green, blue with a decrease in the brightness of radiation sources by 50%. Saturation changes disproportionately, i.e. lowering the saturation to a minimum does not mean that the brightness of the source will be reduced to 50%. If the color is already darker than gray, it will become even darker as the saturation is lowered, and as the saturation decreases further, it will turn completely black.

Such color characteristics as hue (hue), brightness (Brightness), and saturation (Saturation) underlie the color model HSB (otherwise called HCV).

In order to understand these color characteristics, consider the color palette of the Adobe Photoshop graphics editor in Figure 7.

Figure 7 - Adobe Photoshop Color Picker

If you look closely at the picture, you will find a small circle, which is located in the upper right corner of the palette. This circle shows which color is selected on the color palette, in our case it is red. Let's start to understand. First, let's look at the numbers and letters that are located on the right half of the picture. These are the parameters of the HSB color model. The topmost letter is H (hue, color tone). It determines the position of a color in the spectrum. A value of 0 degrees means that it is the highest (or lowest) point on the color wheel - that is, it is red. The circle is divided into 360 degrees, i.e. It turns out that it has 360 color tones. The next letter is S (saturation, saturation). We have a value of 100% - this means that the color will be "pressed" to the right edge of the color palette and have the maximum possible saturation. Then comes the letter B (brightness, brightness) - it shows how high the point is on the color palette and characterizes the intensity of the color. A value of 100% indicates that the color intensity is maximum and the dot is "pressed" to the top edge of the palette. The letters R(red), G(green), B(blue) are the three color channels (red, green, blue) of the RGB model. In each, each of them indicates a number that indicates the amount of color in the channel. Recall the spotlight example in Figure 3, when we figured out that any color can be made by mixing three light beams. By writing numerical data to each of the channels, we uniquely determine the color. In our case, the 8-bit channel and the numbers range from 0 to 255. The numbers in the R, G, B channels indicate the light intensity (color brightness). We have a value of 255 in the R channel, which means that this is a pure red color and it has the maximum brightness. Channels G and B are zeros, which means the complete absence of green and blue colors. In the very bottom column you can see the code combination #ff0000 - this is the color code. Each color in the palette has its own hexadecimal code that defines the color. There is a wonderful article Color theory in numbers, in which the author tells how to determine the color by the hexadecimal code.
In the figure, you can also notice the crossed-out fields of numerical values ​​​​with the letters "lab" and "CMYK". These are 2 color spaces, according to which colors can also be characterized, they are generally a separate conversation and on this stage there is no need to delve into them until you understand RGB.
You can open the Adobe Photoshop Color Palette and play around with the color values ​​in the RGB and HSB fields. You will notice that changing the numeric values ​​in the R, G, and B channels will change the numeric values ​​in the H, S, B channels.

Object color

It's time to talk about how it happens that the objects around us take on their color, and why it changes with different lighting of these objects.

An object can only be seen if it reflects or transmits light. If the object is almost completely absorbs incident light, then the object takes black color. And when the object reflects almost all the incident light, it receives White color. Thus, we can immediately conclude that the color of the object will be determined by the number absorbed and reflected light with which this object is illuminated. The ability to reflect and absorb light is determined by the molecular structure of the substance, in other words, by the physical properties of the object. The color of the object "is not inherent in it by nature"! By nature, it contains physical properties: reflect and absorb.

The color of the object and the color of the radiation source are inextricably linked, and this relationship is described by three conditions.

- First condition: An object can take on color only when there is a light source. If there is no light, there will be no color! Red paint in a can will look black. In a dark room, we cannot see or distinguish colors because there are none. There will be a black color of the entire surrounding space and objects in it.

- Second condition: The color of an object depends on the color of the light source. If the light source is a red LED, then all objects illuminated by this light will have only red, black and gray colors.

- And finally, the third condition: The color of an object depends on the molecular structure of the substance that makes up the object.

Green grass looks green to us because, when illuminated with white light, it absorbs the red and blue wavelengths of the spectrum and reflects the green wavelength (Figure 8).

Figure 8 - Reflection of the green wave of the spectrum

The bananas in Figure 9 look yellow because they reflect the waves that lie in the yellow region of the spectrum (yellow spectrum wave) and absorb all other wavelengths of the spectrum.

Figure 9 - Reflection of the yellow wave of the spectrum

The dog, the one shown in Figure 10, is white. White color is the result of reflection of all waves of the spectrum.

Figure 10 - Reflection of all waves of the spectrum

The color of the object is the color of the reflected wave of the spectrum. This is how objects acquire the color we see.

In the next article, we will talk about a new color characteristic -