The radiant energy that causes the light sensation is called optical radiation, and the power of such radiation is called the light flux.
The visible part of solar radiation at the Earth’s surface is 40% and in the spectrum of its electromagnetic radiation occupies a narrow wavelength range (from 760 to 400 nm). The eye is most sensitive to the middle part of the visible spectrum and has the maximum sensitivity at a wavelength of 555 nm (transitional yellow-green part of the spectrum). This sensitivity is accepted.
for a unit. As you approach the red and blue-violet parts of the spectrum, the sensitivity of the eye decreases sharply. The relative sensitivity of the eye to different parts of the spectrum is called relative visibility.
Luminous flux (F) – the power of radiant energy, estimated by the eye according to the light sensation produced by it. The unit of luminous flux – lumen (lm) – luminous flux emitted by a point source at a light intensity of 1 candela (cd) in a solid angle of 1 steradian (cf); steradian is a solid spatial angle with a vertex in the center of the sphere, cutting out on the surface of the sphere an area equal to the area of a square with a side whose length is equal to the radius of the sphere .
Light intensity (J) is the spatial density of the light flux (part of the light flux) from the light source in a given direction within a certain solid angle. The unit of luminous intensity – candela (cd) – luminous intensity emitted in the perpendicular direction from the source (absolutely black body with an area of 1/600000 m 2 at the solidification temperature of platinum).
Illumination (E) is the surface density of the light flux F incident on the surface S , determined by the formula:
E = F / S
The unit of illumination is lux (lx) – the illumination of a surface with an area of 1 m 2 when the luminous flux incident on it is 1 lm.
The luminous flux incident on the illuminated surface is not always completely reflected from it towards the eye. The decisive role in the process of vision belongs to that part of the light flux, which, being reflected from the illuminated surface, falls on the light-reflecting elements of the eye, which causes a visual sensation. Therefore, from the point of view of the physiology of visual perception, it is not the incident light flux that is important, but the brightness reflected from the illuminated surface .
Brightness (L) – the magnitude of the luminous flux reflected by the illuminated or luminous surface towards the eye. The unit of brightness is candela per square meter (cd / m 2 ) – the brightness of a uniformly luminous flat surface with an area of 1 m 2 , emitting in the direction perpendicular to it a luminous intensity equal to one candela.
The brightness is determined by special devices with bright meters and can be calculated for fixtures in cd / m 2 according to the formula:
L = (E • K) / π
where L is the brightness, cd / m 2 ; E – illumination, lux; K is the reflection coefficient (%); π ≈ 3.14 (pi number). The ratio of light values is shown in Fig. 12 B. The brightness of the luminous surface depends on its emitted
light intensity, the angle at which an object or surface is viewed and from its light properties, since the light flux incident on the surface is partially transmitted and absorbed by the body, and partially reflected. With constant illumination, the brightness of the background or object is greater, the greater its reflectivity, i.e. lightness. The dependence of illumination on the values of brightness and lightness is shown .
N ryamuyu (generated light sources burs – lamps, windows), peripheral (schihsya from a luminous surfaces disposed away from the direction of view of) the reflected (from the mirror surfaces) when working with metal, glass, plastic etc.
Reflection coefficient – the ratio of the reflected light flux (F OTR ) to the incident (F pad ), determined by the formula:
b = F neg / F pad
Reflection coefficients depend on the color of the surface and are accepted as follows: white color – 0.7-0.8; light beige, yellow – 0.5; natural wood color – 0.4; greenish-blue – 0.3; blue – 0.25; light brown, blood color 0.15; brown, blue, purple – 0.1.
Light transmittance (T) – the ratio of the light flux passing through the medium (F prop ) to the incident light flux (F pad ):
T = F prop / F pad
This coefficient allows you to evaluate the quality and cleanliness of window panes, lighting fixtures.
Stroboscopic effect – the phenomenon of distortion of the visual perception of a rotating, moving or alternating 32
The reflective ability of the objects around us is not the same. The optimal brightness level when the work is considered zritel- GOVERNMENTAL brightness of 500 cd / m 2 . Excessively high brightness, causing visual discomfort – glare, is called luster . Distinguish brilliance and illuminating objects in flickering light. It arises when the frequency characteristics of the movement of objects coincide and the luminous flux changes in time in lighting installations with gas-discharge light sources fed by alternating current.