Scattering of light is a change in any characteristics of a falling beam of light when it interacts with matter. In this case, the spatial distribution, frequency, and polarization of the optical radiation change, although often only the transformation of the angular distribution of the light flux is understood as scattering. The term "scattering" in lighting equipment usually refers to the reflected part of the light flux incident on the material and that part of the light stream that passes through the material.
Absorption of light is a decrease in the intensity of light passing through a medium filled with matter.
The light flux Fsv, falling on any body, is in general partially reflected from its surface, partially refracted (passes through the body), partially absorbed by it. By the law of conservation of energy
Ф = Фотр + Фпогл + Фпроп
where Fotr is the reflected part of the light flux;
Fpogl - absorbed part of the light flux;
FPP is the light flux passed through the body.
The ratio of each of the components of the light flux to the light flux incident on the surface is called the reflection coefficient R, the absorption A and the transmission T:
R = Phot / F
A = Phorn / F
T = Фпроп / Ф
There are three types of reflection and light transmission by bodies:
- Directional;
- diffuse (diffuse);
Directional scattered.
Reflection of light is a phenomenon consisting in the fact that when light falls from the first medium to the interface with the second medium, the interaction of light with matter leads to the appearance of a light wave propagating from the interface back to the first medium. The reflection of light can be specular (the reflected beam lies in the plane passing through the incident ray and the normal to the reflecting surface, the angle of reflection is equal to the angle of incidence), diffuse (the scattering of light by the uneven surface of the second medium in all possible directions) and mixed. The bodies with a smooth shiny surface have a directional or mirror image - a mirror, a polished surface. The bodies that reflect light, scattering it so that their brightness becomes the same in all directions of space, have a diffuse reflection - chalk, gypsum, lime.
Refraction of light is a change in the direction of propagation of the incident light beam as it passes through the interface between two media.
Light transmittance (light transmission coefficient) is the ratio of the light flux that has passed through the material to the light flux incident on the surface of the material, or in another way, this is the percentage of the incident light that passes through the thickness of the material.
There are materials:
· With directional transmission (the material does not dissipate the light stream passing through it, the transparent material)
· With diffuse transmission (the material dissipates the entire light flux penetrating into it)
· With mixed transmission (with partial scattering).
Transparency of the material is a quantity that indicates how much of the light flux incident on the surface entering the medium in the form of a parallel beam in order to exclude the effect of the interfaces, passes through the material layer without changing the direction. Transparency is different from transmittance in general, so the transparency differs from transmittance in general: a strongly scattering medium (for example, a sheet of paper) is opaque, although the ratio of the transmitted light flux to the incident flux is large. Transparency depends on the wavelength of the radiation, either monochromatic transparency is spoken, or about transparency in this range, it is usually meant transparency for light radiation in the visible range. Transparent bodies have directional transmission - glass.
The turbidity of the material is a quantity that indicates how much of the light flux incident on the surface passes through the material layer with a change in direction (is dissipated), the deviation from the original direction is taken by more than 2.5 °. The bodies that transmit light scatter it so that their brightness becomes the same in all directions of space, have a diffuse transmission - frosted glass.