Applications and features of visible light and radiation. What is meant by the term 'wavelength of light' Visible light table

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, see. It's that simple.

Wavelength of visible light

And now it's more difficult. The wavelengths of light in the visible region of the spectrum 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. What if human language, then this 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 we see colors within the visible light spectrum

Our eyes can not only perceive these tiny waves, but also distinguish between their lengths 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 main) - approximately 510 nm. And finally, the third one is 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?

Actually, these are two questions, not one. And so we will give two different but related answers. We see a clear sky blue at midday because short wavelengths of light are scattered more efficiently when they collide with gas molecules in the atmosphere than long wavelengths. So the blueness we see in the sky is blue light scattered and reflected many times by atmospheric molecules.

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

But with grass everything is slightly different. It appears 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 appear black because they absorb all wavelengths without reflecting anything, 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, a dog is man's 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 violet and finally visible light disappears. But the light itself did not disappear - it moved into the region of the spectrum called ultraviolet. Although we no longer perceive this part of the light spectrum, it is what makes fluorescent lamps, some types of LEDs, and all sorts of cool glow-in-the-dark things glow. Next comes X-ray and gamma radiation, with which it is better not to deal at all.

At the other end of the visible light spectrum, where red ends, infrared radiation begins, which is more heat than light. It could very 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 how does all this relate to lighting?

Very relevant! Since we have learned a lot about the spectrum of visible light and how we perceive it, lighting equipment manufacturers are 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. The color of the light has become available to have real numbers for comparison and marketing gimmicks. Special lamps began to be produced for various needs: for example, lamps for growing indoor plants, which provide more ultraviolet and light from the red region of the spectrum for better growth and flowering, or “heat lamps” various types, which settled in household heaters, toasters, and grills in “Shaurma from Ashot”.

Hz), and as long-wave - 760-780 nm (395-385 THz). Electromagnetic radiation with these wavelengths is also called visible light , or just light(V in the narrow sense this word).

Story

The first explanations of the causes of the appearance of the spectrum of visible radiation 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, 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 out of a belief (derived from the ancient Greek sophists) that there was a connection between colors, musical notes, solar system objects 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 boundaries of the ranges 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 is in to a large extent depends on the observation conditions.

See also

Notes

1. Gagarin A.P. Light// Physical encyclopedia: [in 5 volumes] / Ch. ed. A. M. Prokhorov. - M.: Great Russian Encyclopedia, 1994. - T. 4: Poynting - Robertson - Streamers. - P. 460. - 704 p. - 40,000 copies. - ISBN 5-85270-087-8.
2. GOST 8.332-78. State system for ensuring the uniformity of measurements. Light measurements. Values ​​of relative spectral luminous efficiency of monochromatic radiation for daytime vision

The electromagnetic spectrum is conventionally 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 appear.
• Range boundaries in wavelengths or frequencies.
• What causes the absorption or emission of waves of a particular range.
• Use of each type of electromagnetic waves.
• Sources of radiation of various electromagnetic waves (natural and artificial).
• The danger of each type of wave.
• Examples of objects having dimensions comparable to the wavelength of the corresponding range.
• The concept of black body radiation.
• Solar radiation and atmospheric transparency windows.

Electromagnetic wave bands

Microwave range

Microwave radiation is used to heat food in microwave ovens, mobile communications, radars (radars), up to 300 GHz easily passes through the atmosphere, therefore it is suitable for satellite communications. Radiometers operate in this range for remote sensing and determining the temperature of different layers of the atmosphere, as well as radio telescopes. This range is one of the key ones for EPR spectroscopy and rotational spectra of molecules. Long-term exposure to the eyes causes cataracts. Mobile 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 based on distributed elements. Waveguides and strip lines are used to transmit energy, and volumetric resonators or resonant lines are used as resonant elements. Man-made sources of microwave waves are klystrons, magnetrons, traveling wave tubes (TWTs), Gunn diodes, and avalanche transit diodes (ATDs). In addition, there are masers, analogues of lasers in long-wavelength ranges.

Microwaves are emitted by stars.

In the microwave range there is the so-called cosmic background microwave radiation (relict radiation), which in its spectral characteristics completely corresponds to the radiation of a completely black body with a temperature of 2.72 K. Its maximum intensity occurs 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 theory Big Bang, which is currently the basis of modern cosmology. The latter, 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 use, emitting in the visible range, the following can be named: 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 summing 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 lasing 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 limited number of generation lines. It was not possible to create semiconductor lasers with a wide bandgap due to enormous technological difficulties. However, eventually they 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 increasing pump frequency (upconversion lasers).

Light sources in the blue-green region make it possible to increase the recording density on a CD-ROM, the quality of reprography, and are necessary for creating full-color projectors, for communication with submarines, for capturing the relief of the seabed, for laser cooling of individual atoms and ions, for monitoring deposition from gas (vapor deposition), in flow cytometry. (taken from “Compact blue-green lasers” by W. P. Risk et al).

Literature:

Ultraviolet range

The ultraviolet range is considered to occupy the region from 10 to 380 nm. Although its boundaries are not clearly defined, especially in the short-wave region. It is divided into subranges and this division is also not unambiguous, since in different sources it is tied to various physical and biological processes.

So on the Health Physics Society website, the ultraviolet range is defined within the range 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 for ultraviolet radiation, but in the table in the text it is divided into a bunch of overlapping subranges, starting from 10 nm. In the Russian version of Wikipedia “Ultraviolet radiation”, from the very beginning, the boundaries of the UV range are set within 10 - 400 nm. In addition, Wikipedia lists the areas 100 – 280, 280 – 315, 315 – 400 nm for the UVC, UVB and UVA ranges.

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, since it is absorbed by the ozone layer of the stratosphere and in the region shorter than 200 nm very strongly by atmospheric oxygen.

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

UVB is the most destructive part of UV radiation, as it has enough energy to damage DNA. It is not completely absorbed by the atmosphere (about 2% passes through). This radiation is necessary for the production (synthesis) of vitamin D, but the harmful effects can lead to 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 tanning, but excess leads to burns. Like UVB, it is necessary for the synthesis of vitamin D. Excessive exposure leads to suppression of the immune system, skin hardness and the formation of cataracts. Radiation in this range is also called black light. Insects and birds are able to see this light.

As an example, the figure below shows the dependence of ozone concentration on height at northern latitudes (yellow curve) and the level of blocking of solar ultraviolet radiation 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 virtually no danger. Ozone blocks most UVB, but some reaches the Earth. If the ozone layer is depleted, most of it will irradiate the surface and cause genetic damage to living things.

A short 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 of food, water, air, objects from microbes (UVC).
• Black light (UVA) in forensic science, in the examination of works of art, in establishing the authenticity of banknotes (fluorescence phenomenon).
• Fake tan.
• Laser engraving.
• Dermatology.
• Dentistry (photopolymerization of fillings).

Man-made sources of ultraviolet radiation are:

Non-monochromatic: Mercury gas-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 average power ranging from several 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 operate in pulsed mode with nanosecond pulses;
4. Some fiber lasers, for example, are doped with neodymium;
5. Some dye lasers are capable of emitting ultraviolet light;
6. Argon ion 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, operating in a pulsed mode with nanosecond pulse duration and a peak power of several megawatts;
8. Tripling frequencies of Nd:YAG laser in nonlinear crystals;

Literature:

1. Wikipedia "Ultraviolet".

SPECTRAL COMPOSITION OF LIGHT

The optical region of the spectrum of electromagnetic radiation consists of three sections: invisible ultraviolet radiation (wavelength 10-400 nm), visible light radiation (wavelength 400-750 nm), perceived by the eye as light, and invisible infrared radiation (wavelength 740 nm - 1- 2 mm).

Light radiation that affects the eye and causes the sensation of color is divided into simple (monochromatic) and complex. Radiation with a specific wavelength is called monochromatic.

Simple radiations cannot be decomposed into any other colors.

Spectrum is a sequence of monochromatic radiation, each of which corresponds to a certain wavelength of electromagnetic vibration.

When white light is decomposed by a prism into a continuous spectrum, the colors in it gradually transform into one another. It is generally accepted that within certain wavelengths (nm) radiation has the following colors:

390-440 – purple

440-480 - blue

480-510 – blue

510-550 – green

550-575 - yellow-green

575-585 - yellow

585-620 – orange

630-770 – red

The human eye is most sensitive to yellow-green radiation with a wavelength of about 555 nm.

There are three radiation zones: blue-violet (wavelength 400-500 nm), green (length 500-600 nm) and red (length 600-680 nm). These spectrum zones are also the zones of predominant spectral sensitivity of the eye receivers and three layers of color photographic film. Light emitted by conventional sources, as well as light reflected from non-luminous bodies, always has a complex spectral composition, that is, it consists of the sum of various monochromatic radiations. The spectral composition of light is the most important characteristic of lighting. It directly affects light transmission when shooting on color photographic materials.

Newton took the first step towards measuring color - he systematized color by hue, constructing color wheel

In addition, Newton conducted experiments on the addition of radiation of different colors, introducing the concept main And additional flowers. He experimentally established that any color can be obtained as the sum of radiations of three colors - blue, green and red - which he named primary colors. This statement formed the basis of the color equation, where color is represented by the sum of radiations of three primary colors (K, Z, S), taken in a certain proportion:

C = kK + zZ + sS,

Where s, z, k – coefficients corresponding to the mixed intensities of blue, green and red radiation. IN foreign literature these intensity values ​​are denoted accordingly R, G, B.

Color wheel- a scheme that systematizes color according to hue. In the spectrum, colors smoothly transition into one another, but there are no purple, lilac, or crimson tones in the spectrum. At the same time, in the color violet we clearly feel the presence of red. Therefore, Isaac Newton arranged all the color tones according to their similarity to each other in a circle. Newton arranged the colors so that complementary colors lay opposite each other. Subsequently, the color wheel changed somewhat

(Goethe's Color Wheel, Munsell's Color Wheel, etc.), where the condition of complementarity of opposite tones is not met.

WITH The next stage in the development of half-body colorimetry of the Ostwald color gamut was the CIE (International Commission on Illumination) schedule. The need for its creation was caused by the fact that not all saturated colors can be obtained from the three primary colors. Some colors obtained by adding primary colors have less saturation than pure spectral colors. And in order for truly any color to be obtained in an additive way, the original primary colors must have a saturation of more than 100%, that is, more saturated than spectral colors. In reality, such colors cannot exist, but such colors were introduced as mathematical abstractions. They were called X, Y, Z - red, green and blue, respectively.

In fact, the MKO chart is a modified color wheel on which colors of 100% saturation are placed. Toward the center, the saturation drops to 0. The CIE graph is often used to indicate the color of the radiation from various light sources.

In addition to the MKO schedule, other colorimetric systems are currently used, for example Lab. Magnitude L determines the brightness of color, A– closeness of color to red or green color tone, b– color close to blue or yellow.

It should be noted that none of the existing colorimetric systems fully reflect all the phenomena of color vision. Therefore, colorimetric systems continue to develop and improve.

The human eye distinguishes colors due to the fact that they have different wavelengths (frequencies). Wavelength is measured in nanometers (nm/nm).

The sensitivity of the human eye to radiation (light) depends on the wavelength. , while the maximum sensitivity occurs at 555 nm, in the green part of the spectrum. Since sensitivity gradually decreases to zero as one moves away from the maximum point, it is impossible to indicate the exact boundaries of the spectral range of visible radiation. Typically, the region of 380–400 nm (790–750 THz) is taken as the short-wave boundary, and 760–780 nm (395–385 THz) as the long-wave boundary. Electromagnetic radiation with these wavelengths is also called visible light, or simply light (in the narrow sense of the word).

Often the wavelength in nanometers or nm is indicated along with the color emitted by LEDs. For example, "blue LED, 440 nm". The wavelength allows you to accurately select LED products of the same color (if, of course, it is indicated at all and indicated correctly).

Perceptible to the human eye electromagnetic radiation with a wavelength from 380 to 760 nm. It is called visible light, or simply light (in the narrow sense of the word). The wavelengths of light visible or perceived by humans lie in the range of 380 - 760 nm.

Visible and invisible (ultraviolet and infrared) parts of the spectrum