The optical region of the spectrum of electromagnetic radiation is divided into ultraviolet, visible and infrared.
Visible radiation (light, a beam of light, a stream of light) is radiation that, upon reaching the reticular shell of the eye, can cause a visual sensation.
Ultraviolet radiation: wavelengths from 1 to 380 nm.
Visible radiation: wavelengths from 380 to 760 nm.
Infrared radiation: wavelengths from 760 nm to 1 mm.
The visible part of the spectrum consists of the following color bands:
- Red - 760 ... 630 nm;
- orange - 630 ... 600 nm:
- yellow - 600 ... 570 nm;
- green - 570 ... 490 nm;
- blue - 490 ... 450 nm;
- blue - 450 ... 430 nm;
- purple - 430 ... 380 nm.
In practice, it is often necessary to deal with bodies emitting light of a complex spectral composition consisting of waves of different lengths. The energy of visible radiation affects the photosensitive elements of the eye and produces a light sensation, the intensity of which depends on the radiation power and the wavelength. This is due to the different sensitivity of the eye to radiation with different wavelengths. At the same radiation power of each of the wavelengths, the greatest light sensation occurs when the green light is emitted at a wavelength of 555 nm. Blue radiation of the same power is perceived at about 20, and red radiation is 50 times weaker.
The radiation flux (Φ, W) is the ratio of the energy transferred by electromagnetic radiation through a surface to the time of transfer, which is much longer than the period of electromagnetic oscillations. The radiation flux is measured in W.
Light values are the reduced photometric values formed from energy photometric values by means of the spectral light efficiency of monochromatic radiation for daytime vision. From energy, light values differ in that they characterize light in view of its ability to evoke visual sensations in a person. Form a system of light photometric quantities. As units of measurement of light quantities, special light units are used, based on the unit of light intensity "candela".
Candela (cd) is a unit of light intensity equal to the intensity of light in a given direction of the source emitting monochromatic radiation at a frequency of 540.1012 Hz (which corresponds to a wavelength of 555 nm) whose light intensity in this direction is 1/683 W /
The luminous flux (FS, lm) is the reduced radiation flux used to characterize the effect of radiation in the optical frequency range on the human eye and is measured in lumens (lm). The luminous flux is a quantity proportional to the radiation flux estimated in accordance with the spectral sensitivity of the average human eye, for which the concept of the spectral luminous efficacy of monochromatic radiation is used. There is also a concept - the mechanical equivalent of light: the ratio of the radiation flux to the light flux contained in it. 1 watt of radiation with a wavelength of 555 nm corresponds to a light flux equal to 683 lm.
1 lumens (lm) is equal to the light flux emitted by a point source having a light intensity equal to 1 candle, into an angle equal to 1 steradian (1 lm = 1 cd × cp). The magnitude of the total light flux, which creates a source that has the strength of light in 1 candle, is 4p lumens.
The mechanical equivalent of light is the ratio of the total radiation flux (radiation power) to the light flux contained in it (depends on the wavelength of light). For a light length of 555 nm, the mechanical equivalent of light has the smallest value of 0.00146 W / lm.
The spectral luminous efficiency of monochromatic radiation is a physical quantity that characterizes the sensitivity of the human eye to the influence of monochromatic light on it (depends on the wavelength of light) and has the dimension lm / W.
The solid angle (Ω, φ) is a part of the space bounded by a conical surface. The value of the solid angle is defined as the ratio of the area of the spherical surface S on which it rests to the square of the radius of the sphere r. The unit of the solid angle is steradian (cp). The value of the solid angle in 1cp is the solid angle, which cuts on the surface of the sphere an area equal to the square of the radius of the given sphere. The full sphere forms a solid angle equal to 4π.
The intensity of light (I, cd) is one of the main light values that characterizes the glow of a source of visible radiation in a certain direction. The intensity of light is equal to the ratio of the light flux propagating from the source inside the elementary solid angle containing this direction, to this solid angle: I = dFсв / dΩ. The strength of light is measured in candela (cd). If the light flux is uniformly distributed in space, then I = Фсв / Ω.
Illuminance (E, lk) is the light quantity determined by the ratio of the light flux incident on a small portion of the surface to the area of this section: E = dFcv / dS. The unit of measurement of illumination is lux (lux). If the light flux is distributed uniformly in space, then E = Фсв / S.
Brightness (L, cd / m2) is the surface-spatial density of light