Visible radiation

You probably heard about special electromagnetic waves perceived by the human eye, occupying a certain part of the spectrum and having a wavelength of 380 nm (for violet) to 780 nm (for red). This is the visible radiation. Its properties, indicated usually in terahertz, we can learn by measuring the frequency range of such waves (we will get a gap of 400-790 THz). Visible radiation is also called visible light. To put it more simply, this is the light that we are so used to and that we do not even think about the physical side. The most sensitive to our eye is the 555 nm (this is the green part of the spectrum, 540 THz).

Interesting fact: the spectrum does not contain some colors, perceived by us. For example, it does not have a pink color (and its shades). It is formed when other colors are mixed.

Have you ever wondered why the sky seems blue? It's simple: a part of the spectrum with a short wavelength is scattered by air more strongly than with a length corresponding to the red side of the spectrum. Due to this the sky has a blue color, especially at noon time. Visible radiation enters the so-called "optical window". This terrestrial atmosphere does not absorb this region of the spectrum.

Some animals see radiation that is inaccessible to human sight (it simply does not enter the range we see). Many insects (for example, bees) perceive the ultraviolet range, so they quickly find nectar in flowers. Ultraviolet radiation can see birds. Some species of birds even have marks that are noticeable only in this kind of radiation, in which the male and female unmistakably determine each other.

The visible radiation has also found application in humans. Its most common form is thermal, based on the motion of atoms: the more the body warms up, the faster the movement of atoms, which emit light in a collision. All the sources of light familiar to us - the Sun, the incandescent lamp, the candle (the flame) - are the thermal sources of visible radiation.

The next example is electroluminescence. Here, the energy that causes the emission of light, the atoms are derived from nonthermal sources. When discharges in a gas, an electric field is informed by some kinetic energy, electrons strike atoms (the term "collide" is used), and the energy of excited atoms is already observed in the form of luminescence (electroluminescence).

Electroluminescence is now used in advertising glowing inscriptions. By the way, the northern lights also refer to the manifestation of electroluminescence: charged particles are emitted by the Sun, attracted by the magnetic field of our planet, are excited at its poles and glow. But the cathode-ray tubes in the television set glow due to cathodoluminescence: the glow is caused by bombardment by electrons.

Chemiluminescence is another example of visible radiation. Here, the result of the glow is the energy released during chemical reactions. The temperature of the light source is equal to the temperature of the medium in which it is located. An example could well be a firefly with a small glowing green "flashlight". Other organisms also shine: some fish, bacteria, insects. Sometimes you can see the glow of decaying trees.

Some bodies begin to glow after being in the light: they absorb energy, they themselves become sources of light. This is photoluminescence, the properties of which are actively used in paints, clothing, road signs, etc.

Color components of visible light are used in the practice of psychologists: green color is known to soothe, red - excites, purple, black and blue - on the contrary, inhibit and even depress, and when there is a lack of white, a person is depressed at all. Visible radiation is used in medicine (chromotherapy): for example, yellow light is used in the treatment of certain eye diseases. Some diseases and pathologies of the sexual glands are treated with red light: infantilism, infertility, menstrual cycle disorders in women, insufficiency of semen in men, extinction of sexual desire. Blue light eliminates itching, treats exudative diathesis and various types of hemorrhage.