|
Color |
ρ |
Color |
ρ |
Color |
ρ |
Color |
ρ |
|
Green light |
light gray |
Blue light | |||||
|
yellow light |
Green Medium |
Gray Medium |
Blue dark | ||||
|
yellow medium |
Green dark |
Gray dark |
Brown dark | ||||
The values of the reflection coefficients of some specific surfaces are given in Table. 5.
Due to the fact that objects with different brightness can fall into the field of view, it is introduced concept of adaptive brightness (B A ), which is understood as the brightness to which the visual analyzer is adapted (tuned) at a given time. Approximately, we can assume that for images with direct contrast, the adaptive brightness is equal to the brightness of the background, and for images with reverse contrast, it is equal to the brightness of the object. The sensitivity range of the visual analyzer is very wide: from 10 -6 to 10 6 cd/m 2 . The best working conditions correspond to the levels of adaptive brightness ranging from several tens to several hundreds cd/m 2 .
Table 5
The values of the reflection coefficients of some surfaces
|
Surface |
ρ |
Surface |
ρ |
|
Polished steel |
Paper white thin | ||
|
Iron white |
Whatman paper | ||
|
Molybdenum |
White lead | ||
|
polished aluminum |
White zinc | ||
|
Brushed aluminum |
Faience plate white | ||
|
Aluminized mirror |
White tile | ||
|
Brass matte |
Marble white | ||
|
polished brass |
Brick white | ||
|
Brick yellow | |||
|
brick red | |||
|
Milk glass (2 - 3 mm) |
Window glass | ||
|
White porcelain enamel | |||
|
Velvet black |
white glue paint |
It should be borne in mind that providing the required contrast value is only a necessary, but still insufficient condition for the normal visibility of objects. You also need to know how this contrast is perceived in given conditions. For its assessment of the visual perception of objects, the concept is introduced threshold contrast :
Where B since - threshold brightness difference, i.e. the minimum difference between the brightness of the object and the background, which is still detected by the eye. Thus, the value TO since determined by the differential discrimination threshold. To obtain an optimal operational discrimination threshold, it is necessary that the actual value of the difference between the brightness of the object and the background be 10–15 times greater than the threshold value. This means that for normal visibility, the contrast value calculated by formulas (1) must be greater than the value TO since 10 - 15 times. Thus, the ratio of the contrast value of the object of observation to its value (characteristic of the ability of the eye to perceive the object) is called visibility :
. (4)
The value of the threshold contrast depends on the brightness of the background and on the angular dimensions α about observation of objects. It should be noted that larger objects are visible at lower contrasts, and that the required threshold contrast decreases with increasing brightness.
For an approximate estimate of the magnitude of the direct threshold contrast, the paper proposes an empirical formula:
,
(5)
Where: α about is the angular size (measured in arc minutes) of the observed object (see Fig. 4 below). Functional coefficients φ 1 (α about ) And φ 2 (α about ) depend on the angular size of the observed object and the brightness of the background:
;
(5 1)
For 0,01 ≤ B f ≤ 10 – k φ1 = 75;
;
(5 2)
For B f > 10 – k φ1 = 122;
;
(5 3)
k φ2 = 0,333; ξ = 3,333; p 0 = –0,096, p 1 = –0,111, p 2 = 3,55∙10 – 3 , p 3 = –4,83∙10 – 5 , p 4 = 1,634∙10 – 7 ; q 0 = 2,345∙10 – 5 , q 1 = –0,034, q 2 = 1,32∙10 – 3 , q 3 = –2,053∙10 – 5 , q 4 = 7,334∙10 – 4 .
Formulas (5 1) - (5 3) are obtained as a result of approximation of the tabular values of the functional coefficients φ 1 (α about ) And φ 2 (α about ) , given in .
To estimate the value of the inverse threshold contrast for 1′ ≤ α about ≤ 16′ an approximation of another empirical formula is proposed:
,
(6)
Where: r 0 = –0,51, r 1 = -0,151, r 2 = 3,818∙10 –3 , r 3 = –3,94∙10 –5 , r 4 = –1,606∙10 –7 , r 5 = 2,095∙10 –10 .
When the angular sizes of the observed objects exceed 16 arc minutes ( α about > 16′), you can use the formula:
, (6′)
Where K por(16′) is the threshold contrast value calculated by formula (6) for α about = 16′ .
The relationship between the angular and linear dimensions of the observed objects for the general case is illustrated in Fig. . 4, where: l about –linear size of the observed object; l x And l y are the distances from the observation point (location of the human eye) to the center of the observed object, taken horizontally and vertically, respectively; β about is the angle of deviation of the plane of the observed object from the horizontal. Quantities l about ,l x ,l y And β about determined by the characteristics and organization of a particular workplace. The rest, indicated in Fig. 4 quantities are auxiliary: l embankment is the direct distance from the observation point to the center of the observed object; h embankment is the normal distance from the observation point to the plane of the observed object; β embankment is the angle of view relative to the plane of the observed object; α 1 And α 2 - auxiliary corners.
Rice. 4. Connection of angular ( α ) and linear ( l O) sizes of observed objects
The geometry of the drawing in fig. 4 defines the following expressions for auxiliary quantities:
;
;
(7)
;
(8)
and, therefore, the angular size of the observed object can be determined as:
α about = α 2 – α 1 . (9)
The magnitude of external illumination has a great influence on the conditions of visibility of objects. However, this effect will be different when working with images that have direct or reverse contrast. An increase in illumination with direct contrast leads to an improvement in visibility conditions (value TO etc increases) and, conversely, with reverse contrast - to a deterioration in visibility (the value TO about decreases).
With an increase in illumination, the value TO etc increases because the brightness of the background increases more than the brightness of the object (the reflectance of the background is greater than the reflectance of the object). Value TO about at the same time, it decreases, since the brightness of the object practically does not change (the object glows), and the brightness of the background increases.
In many cases, light signals of varying intensity may be in the operator's field of vision. At the same time, excessive bright objects can cause an undesirable state of the organs of vision - blindness. Especially strong Negative influence the work of the organs of vision is affected by elements with high brightness, which can be excessively bright parts of lamps (for example, the filament of incandescent lamps) or other light sources - direct action, as well as their mirror reflections - reflected action. Blinding brightness is determined by the size and brightness of the luminous surface, as well as the level of brightness of adaptation of the organs of vision. The minimum brightness levels that begin to cause a blinding effect can be approximately determined by the empirical formula:
, (10)
Where Ω cn is the solid angle of observation of the luminous surface by the operator (in steradians), the value of which can be approximately determined as the ratio of the area of the luminous surface to the square of the distance from this surface to the organs of vision.
It should be borne in mind that the actual brightness levels of the observed objects should be estimated using formulas (2) and (3), and with the help of formula (10), only a check of the actual brightness levels for the appearance of a blinding effect can be carried out. For normal perception of the brightness of the observed objects, it is necessary that the following inequality is fulfilled:
B cn < B cn min , (11)
Where B cn is the brightness of the blinding surface, determined by formulas (2) - (3).
Thus, in order to create optimal conditions for visual perception, it is necessary not only to ensure the required level of brightness and contrast of perceived light signals, but also to eliminate excessive uneven distribution of brightness in the field of view. In cases where it is impossible to use formula (9), you can use the data in Table. 6 or consider the uneven distribution of brightness levels in the field of view as acceptable if their difference does not exceed 1 to 30 .
Table 6
Reflection coefficient is a dimensionless physical quantity that characterizes the ability of a body to reflect radiation incident on it. Greek is used as a letter or latin .
Definitions
Quantitative reflection coefficient is equal to the ratio radiation flux reflected by the body to the flux incident on the body:
The sum of the reflection coefficient and the coefficients of absorption, transmission and scattering is equal to one. This statement follows from the law of conservation of energy.
In those cases where the spectrum of the incident radiation is so narrow that it can be considered monochromatic, one speaks of monochromatic reflection coefficient. If the spectrum of radiation incident on the body is wide, then the corresponding reflection coefficient is sometimes called integral.
In the general case, the value of the reflection coefficient of a body depends both on the properties of the body itself and on the angle of incidence, spectral composition, and polarization of the radiation. Due to the dependence of the reflection coefficient of the surface of the body on the wavelength of the light incident on it, the body is visually perceived as painted in one color or another.
Specular reflection coefficient
It characterizes the ability of bodies to mirror the radiation incident on them. Quantitatively determined by the ratio of the specularly reflected radiation flux to the falling stream:
Specular (directional) reflection occurs when radiation is incident on a surface whose irregularities are much smaller than the radiation wavelength.
Diffuse reflectance
Characterizes the ability of bodies to diffusely reflect the radiation incident on them. Quantitatively determined by the ratio of the diffusely reflected radiation flux to the falling stream:
If both specular and diffuse reflections occur simultaneously, then the reflection coefficient is the sum of the coefficients of the mirror image and diffuse reflections:
see also
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Notes
An excerpt characterizing the reflectance (optics)
- Oh, Natasha! - she said.- Did you see it? Did you see? What did you see? cried Natasha, holding up the mirror.
Sonya didn’t see anything, she just wanted to blink her eyes and get up when she heard Natasha’s voice saying “by all means” ... She didn’t want to deceive either Dunyasha or Natasha, and it was hard to sit. She herself did not know how and why a cry escaped her when she covered her eyes with her hand.
- Did you see him? Natasha asked, grabbing her hand.
- Yes. Wait ... I ... saw him, ”Sonya said involuntarily, still not knowing who Natasha meant by his word: him - Nikolai or him - Andrei.
“But why shouldn’t I tell you what I saw? Because others see it! And who can convict me of what I saw or did not see? flashed through Sonya's head.
“Yes, I saw him,” she said.
- How? How? Is it worth it or is it lying?
- No, I saw ... That was nothing, suddenly I see that he is lying.
- Andrey lies? He is sick? - Natasha asked with frightened fixed eyes looking at her friend.
- No, on the contrary - on the contrary, a cheerful face, and he turned to me - and at the moment she spoke, it seemed to her that she saw what she was saying.
- Well, then, Sonya? ...
- Here I did not consider something blue and red ...
– Sonya! when will he return? When I see him! My God, how I’m afraid for him and for myself, and I’m scared for everything ... - Natasha spoke, and without answering a word to Sonya’s consolations, she lay down in bed and long after the candle was put out, with her eyes open, lay motionless on bed and looked at the frosty, moonlight through the frozen windows.
Soon after Christmas, Nikolai announced to his mother his love for Sonya and his firm decision to marry her. The countess, who had long noticed what was happening between Sonya and Nikolai, and was expecting this explanation, silently listened to his words and told her son that he could marry whomever he wanted; but that neither she nor his father would give him blessings for such a marriage. For the first time, Nikolai felt that his mother was unhappy with him, that despite all her love for him, she would not give in to him. She, coldly and without looking at her son, sent for her husband; and when he arrived, the countess wanted to briefly and coldly tell him what was the matter in the presence of Nikolai, but she could not stand it: she burst into tears of annoyance and left the room. The old count began to hesitantly admonish Nicholas and ask him to abandon his intention. Nicholas replied that he could not change his word, and his father, sighing and obviously embarrassed, very soon interrupted his speech and went to the countess. In all clashes with his son, the count did not leave the consciousness of his guilt before him for the disorder of affairs, and therefore he could not be angry with his son for refusing to marry a rich bride and for choosing a dowry Sonya - only on this occasion did he more vividly recall that, if things had not been upset, it would be impossible for Nicholas to wish for a better wife than Sonya; and that only he, with his Mitenka and his irresistible habits, is to blame for the disorder of affairs.
Light on collision reflective surface.
It lies in the fact that falling, And reflected Ray placed in a single plane with a perpendicular to the surface, and this perpendicular divides the angle between the indicated rays into identical components.
It is often simplified as follows: corner fall and angle reflections Sveta the same:
α = β.
The law of reflection is based on the features wave optics. It was experimentally substantiated by Euclid in the 3rd century BC. It can be considered a consequence of the use Fermat's principle For mirror surface. Also, this law can be formulated as a consequence of the Huygens principle, according to which any point of the medium, to which the perturbation has reached, acts as a source secondary waves.
Any medium specifically reflects and absorbs light radiation . The parameter describing the reflectivity of the surface of a substance is denoted as reflection coefficient(ρ orR) . Quantitatively, the reflection coefficient is equal to the ratio radiation flux, reflected by the body, to the flow that hit the body:
Light is completely reflected from a thin film of silver or liquid mercury deposited on a sheet of glass.
Allocate diffuse And mirror reflection.
