What is light?

A person receives most of the information about the world through the organs of vision. But the eyes themselves are able to see only one type of energy - electromagnetic, and even then in a very narrow light range. So what is light? What are the known sources of visible radiation a person uses? What is the dual nature of light? And what are its main properties? Now we find out the answers to these questions.

Light as an electromagnetic wave

Light is considered an electromagnetic wave that a human eye can see. For this, the length of this wave should not exceed the limits from 380-400 nm to 760-780 nm. After 780 nm, the infrared range begins, which a person can feel like heat, and ultraviolet radiation is in front of the visible spectrum. Some insects and birds are able to see it, and human skin can react to it with a tan. The visible electromagnetic spectrum itself is divided into segments, each of which is perceived by a person as light of a certain color. For example, violet corresponds to the wavelength of 380-440 nm, green - 500-565 nm, and red - 625-740 nm.A total of 7 primary colors of the visible spectrum are distinguished, they can be observed by looking at the rainbow. But white light - a mixture of all the colors of the spectrum.

Sources of light

The light source is heated to a certain temperature or excited substance. Light enters the Earth from the Sun, other stars, some heated planets, comets and other celestial bodies. On our planet, the source of light can be a fire - a fire, a candle flame, a torch or an oil lamp, as well as a heated substance. The man also invented artificial sources of visible radiation, in particular, an incandescent lamp, where light emits a tungsten coil heated by electric current, a fluorescent lamp, in which a phosphor layer excited by electrical discharge in the gas filling the flask, a halogen lamp, a mercury lamp, and others glow.

Light properties


Visible electromagnetic radiation propagates in vacuum and homogeneous transparent media in a straight line with a speed of light equal to about 300,000 km / s. At the same time, light has many other properties. For example, light is reflected from opaque surfaces, with the angle of incidence equal to the angle of reflection.As a result, the light reflected from objects is perceived by the eye and allows you to see these objects. Also note that the moon and some planets are not sources of light, but we see them because these celestial bodies reflect the radiation of the sun.


In the transition between two media with different optical densities, light is able to refract. Let us say, when a beam passes from air to water, because of the different optical density of these media, the speed and direction of movement of light in them changes. That is why the spoon in a glass of water seems a bit broken, and the pebbles at the bottom of the lake seem closer than they really are.

Interference and diffraction

The wave nature of light is manifested in its properties such as interference and diffraction. The first property is the ability of several waves to fold into a resultant wave, the parameters of which at different points are noticeably strengthened or weakened. The result of the interference of light can be observed in the form of a game of rainbow streaks on soap bubbles, oil stains or insect wings. And diffraction is the ability of a wave of light to bend around an obstacle and fall into the area of ​​its geometric shadow, for example, the scattering of light on water droplets in the form of rainbow clouds.

Light as a stream of particles

At the same time, light has not only wave properties, and in some cases behaves like a stream of particles — photons. In particular, the regularities of the photoelectric effect, when light incident on a substance pulls electrons out of it, can be explained only from the point of view of the corpuscular theory of light, which represents electromagnetic radiation in the form of a photon flux. However, the wave and photon theory of light not only do not contradict each other, but complement each other. In the scientific community they talk about wave-particle duality of light, which explains what light is, reveals its properties as waves and as a stream of particles.

Date: 08.10.2018, 18:16 / Views: 41551

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