Light is considered to be any kind of optical radiation. In other words, these are electromagnetic waves whose length is in the range of units of nanometers.
General definitions
From the point of view of optics, light is electromagnetic radiation that is perceived by the human eye. It is customary to take the area in a vacuum of 750 THz as the unit of change. This is the short-wavelength edge of the spectrum. Its length is 400 nm. As for the border of wide waves, a unit of 760 nm, that is, 390 THz, is taken as the unit of measurement.
In physics, light is considered as a collection of directed particles called photons. The speed of wave distribution in a vacuum is constant. Photons have a certain momentum, energy, zero mass. In a broader sense, light is visible ultraviolet radiation. Also, the waves can be infrared.
From the point of view of ontology, light is the beginning of being. This is stated by both philosophers and religious scholars. In geography, this term is used to refer to individual regions of the planet. Light itself is a social concept. Nevertheless, in science it has specific properties, features and laws.
Nature and light sources
Electromagnetic radiation is created during the interaction of charged particles. The optimal condition for this is heat, which has a continuous spectrum. The maximum radiation depends on the temperature of the source. A great example of a process is the sun. Its radiation is close to that of an absolutely black body. The nature of light on the Sun is determined by a heating temperature of up to 6000 K. Moreover, about 40% of the radiation is within sight. The maximum of the power spectrum is located near 550 nm.
Light sources can also be:
- Electronic shells of molecules and atoms during the transition from one level to another. Such processes make it possible to achieve a linear spectrum. An example is LEDs and discharge lamps.
- Cherenkov radiation, which is formed during the movement of charged particles with the phase velocity of light.
- The processes of inhibition of photons. As a result, synchro- or cyclotron radiation is formed.
The nature of light can also be associated with luminescence. This applies to both artificial sources and organic. Example: chemiluminescence, scintillation, phosphorescence, etc.
In turn, light sources are divided into groups relative to temperature indicators: A, B, C, D65. The most complex spectrum is observed in a completely black body.
Light characteristics
The human eye subjectively perceives electromagnetic radiation as a color. So, light can give out white, yellow, red, green tints. This is only a visual sensation that is associated with the frequency of the radiation, whether it is spectral or monochromatic in composition. It is proved that photons can propagate even in a vacuum. In the absence of matter, the flow velocity is 300,000 km / s. This discovery was made in the early 1970s.
At the boundary of the media, the light stream experiences either reflection or refraction. During propagation, it dissipates through the substance. We can say that the optical parameters of the medium are characterized by a refraction value equal to the ratio of the velocities in vacuum and absorption. In isotropic substances, the flow distribution is independent of direction. Here, the refractive index is represented by a scalar quantity determined by coordinates and time. In an anisotropic medium, photons appear as a tensor.
In addition, the light is polarized and not. In the first case, the wave vector will be the main value of the determination. If the flow is not polarized, then it consists of a set of particles directed in random directions.
The most important characteristic of light is its intensity. It is determined by photometric quantities such as power and energy.
The main properties of light
Photons can not only interact with each other, but also have a direction. As a result of contact with an extraneous medium, the flow experiences reflection and refraction. These are two fundamental properties of light. With reflection, everything is more or less clear: it depends on the density of matter and the angle of incidence of the rays. However, the situation is much more complicated with refraction.
To begin with, you can consider a simple example: if you lower the straw into the water, then from the side it will seem curved and shortened. This is the refraction of light that occurs at the boundary of a liquid medium and air. This process is determined by the direction of the distribution of rays during passage through the boundary of matter.
When a stream of light touches the boundary between the media, its wavelength changes significantly. However, the frequency of propagation remains the same. If the beam is not orthogonal with respect to the boundary, then both the wavelength and its direction will undergo a change.
Artificial refraction of light is often used for research purposes (microscopes, lenses, magnifiers). Also, such sources of changes in the characteristics of the wave include glasses.
Light classification
Currently, artificial and natural light are distinguished. Each of these species is determined by a characteristic radiation source.
Natural light is a collection of charged particles with a chaotic and rapidly changing direction. Such an electromagnetic field is caused by an alternating fluctuation in tension. Natural sources include red-hot bodies, the sun, polarized gases.
Artificial light is of the following types:
- Local. It is used at the workplace, in the kitchen area, walls, etc. Such lighting plays an important role in interior design.
- Common. This is a uniform illumination of the entire area. Sources are chandeliers, floor lamps.
- Combined. A mixture of the first and second types to achieve perfect illumination of the room.
- Emergency. It is extremely useful for blackouts. Power is produced most often from batteries.
sunlight
Today it is the main source of energy on Earth. It is no exaggeration to say that sunlight affects all important matters. This is a quantitative constant that determines energy.
In the upper layers of the earth's atmosphere contains about 50% of the infrared radiation and 10% of ultraviolet. Therefore, the quantitative component of visible light is only 40%.
Solar energy is used in synthetic and natural processes. This is photosynthesis, and the conversion of chemical forms, and heating, and much more. Thanks to the sun, mankind can use electricity. In turn, the streams of light can be direct and scattered if they pass through the clouds.
Three main laws
Since ancient times, scientists have been studying geometric optics. The following laws of light are fundamental today:
- The law of distribution. It states that in a homogeneous optical medium, light will be distributed in a straight line.
- The law of refraction. A ray of light incident on the boundary of two media and its projection from the point of intersection lie on the same plane. This also applies to the perpendicular lowered to the point of contact. In this case, the ratio of the sines of the angles of incidence and refraction will be a constant value.
- The law of reflection. A ray of light descending to the boundary of the media and its projection lie on the same plane. The angles of reflection and incidence are equal.
Light perception
The surrounding world is visible to man due to the ability of his eyes to interact with electromagnetic radiation. Light is perceived by retinal receptors, which can capture and respond to the spectral range of charged particles.
A person has 2 types of sensitive eye cells: cones and rods. The first determine the mechanism of vision in the daytime at a high level of lighting. Sticks are more sensitive to radiation. They allow a person to see at night.
Visual shades of light are determined by the wavelength and its directivity.