Light is considered to be any kind of optical radiation. In other words, these are electromagnetic waves, the length of which 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 an area in a vacuum of 750 THz as a unit of change. This is the short-wavelength edge of the spectrum. Its length is 400 nm. As for the boundary of wide waves, then the unit of measurement is taken as a section of 760 nm, that is, 390 THz.
In physics, light is considered as a set of directional particles called photons. The velocity of distribution of waves in vacuum is constant. Photons have a certain momentum, energy, zero mass. In a broader sense, light is visible ultraviolet radiation. Waves can also be infrared.
From the point of view of ontology, light is the beginning of being. This is what philosophers and religious scholars say. In geography, this term is used to refer to certain areas of the planet. Light itself is a social concept. Nevertheless, in science it has specific properties, traits and laws.
Nature and light sources
Electromagnetic radiation is created in the process of interaction of charged particles. The optimal condition for this will be 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 a completely black body. The nature of light on the Sun is determined by the temperature of heating up to 6000 K. At the same time, about 40% of the radiation is within visibility. The maximum 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. Examples are LEDs and gas discharge lamps.
- Cherenkov radiation, which is formed when charged particles move at the phase speed of light.
- Processes of photon deceleration. As a result, synchro- or cyclotron radiation is produced.
The nature of light can also be associated with luminescence. This applies to both artificial sources and organic ones. Example: chemiluminescence, scintillation, phosphorescence, etc.
In turn, light sources are divided into groups according 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, the light can give off white, yellow, red, green tints. It's onlyvisual sensation, which is associated with the frequency of radiation, whether it is spectral or monochromatic in composition. Photons have been proven to propagate even in a vacuum. In the absence of matter, the flow velocity is 300,000 km/s. This discovery was made back in the early 1970s.
At the boundary of media, a stream of light experiences either reflection or refraction. During propagation, it dissipates through matter. It can be said that the optical indices of the medium are characterized by a refraction value equal to the ratio of the velocities in vacuum and absorption. In isotropic substances, the propagation of the flow does not depend on the direction. Here, the refractive index is represented by a scalar value determined by coordinates and time. In an anisotropic medium, photons appear as a tensor.
Besides, light can be polarized and not. In the first case, the main quantity of the definition will be the wave vector. 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 such photometric quantities as power and energy.
Basic properties of light
Photons can not only interact with each other, but also have a direction. As a result of contact with a foreign medium, the flow experiences reflection and refraction. These are the 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, with refraction, the situation is farharder.
To begin with, we can consider a simple example: if you lower a straw into water, then from the side it will seem curved and shortened. This is the refraction of light, which occurs at the boundary of the liquid medium and air. This process is determined by the direction of distribution of rays during the passage through the boundary of matter.
When a stream of light touches the boundary between media, its wavelength changes significantly. However, the propagation frequency remains the same. If the beam is not orthogonal to the boundary, then both the wavelength and its direction will change.
Artificial refraction of light is often used for research purposes (microscopes, lenses, magnifiers). Points also belong to such sources of changes in wave characteristics.
Classification of light
Currently, a distinction is made between artificial and natural light. Each of these species is defined by a characteristic radiation source.
Natural light is a set of charged particles with a chaotic and rapidly changing direction. Such an electromagnetic field is caused by a variable fluctuation of intensities. Natural sources include hot bodies, the sun, polarized gases.
Artificial light is of the following types:
- Local. It is used in the workplace, in the kitchen area, walls, etc. Such lighting plays an important role in interior design.
- General. This is uniform illumination of the entire area. Sources are chandeliers, floor lamps.
- Combined. A mixture of the first and second types to achieve the ideal illumination of the room.
- Emergency. It is extremely useful during power outages. Power is most often supplied from batteries.
Sunshine
Today it is the main source of energy on Earth. It would not be an exaggeration to say that sunlight affects all important matters. This is a quantity constant that defines energy.
The upper layers of the earth's atmosphere contain about 50% infrared and 10% ultraviolet radiation. Therefore, the amount of visible light is only 40%.
Solar energy is used in synthetic and natural processes. This is photosynthesis, and the transformation of chemical forms, and heating, and much more. Thanks to the sun, humanity can use electricity. In turn, streams of light can be direct and diffuse if they pass through clouds.
Three main laws
Since ancient times, scientists have been studying geometric optics. Today, the following laws of light are fundamental:
- 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 the valueconstant.
- The law of reflection. A ray of light descending onto the boundary of the media and its projection lie on the same plane. In this case, the angles of reflection and incidence are equal.
Light perception
The surrounding world is visible to a person due to the ability of his eyes to interact with electromagnetic radiation. Light is perceived by retinal receptors, which can detect and respond to the spectral range of charged particles.
A person has 2 types of sensitive cells in the eye: cones and rods. The first determine the mechanism of vision in the daytime with a high level of illumination. Rods are more sensitive to radiation. They allow a person to see at night.
Visual shades of light are determined by the wavelength and its directionality.
