Dark adaptation time of a normal eye. Vision adaptation

When moving from bright light to total darkness(so-called dark adaptation) and during the transition from darkness to light (light adaptation). If the eye, which was previously in bright light, is placed in darkness, then its sensitivity increases rapidly at first, and then more slowly.

The process of dark adaptation takes several hours, and by the end of the first hour the sensitivity of the eye increases several times, so that the visual analyzer is able to distinguish changes in the brightness of a very weak light source caused by statistical fluctuations in the number of emitted photons.

Light adaptation is much faster and takes 1-3 minutes at medium brightness. Such large changes in sensitivity are observed only in the eyes of humans and those animals whose retina, like that of humans, contains rods. Dark adaptation is also characteristic of cones: it ends faster and the sensitivity of cones increases only 10-100 times.

Dark and light adaptation of the eyes of animals have been studied by studying the electrical potentials that arise in the retina (electroretinogram) and in the optic nerve under the action of light. The results obtained are generally consistent with the data obtained for humans by the adaptometry method, based on the study of the appearance of a subjective sensation of light in time after a sharp transition from bright light to complete darkness.

Links

Lavrus V. S. Chapter 1. Light. Light, vision and color // Light and heat. - International public organization"Science and Technology", October 1997. - S. 8.

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See what "Eye adaptation" is in other dictionaries:

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DARK ADAPT, slow sensitivity change human eye at the moment when a person from a brightly lit space enters an unlit one. The change occurs due to the fact that in the RETINA of the eye, with a decrease in the total ... ...

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Books

The Painted Veil: Intermediate A Book to Read, Maugham William Somerset. Written in 1925 by British classicist William Somerset Maugham, the title of the novel The Patterned Veil reflects the lines of Percy Bysshe Shelley's sonnet Lift not thepainted veil which...

It is known that the human eye is able to work in a very wide range brightness. However, the eye cannot perceive the entire range at the same time. In the process of vision, the eye adapts to the level of brightness prevailing in the field of view. This phenomenon is explained by the dependence of the light sensitivity of the eye on the level of excitation of its photosensitive elements. The maximum light sensitivity of the eye has after a long stay in the dark. In the light, the sensitivity of the eye decreases. Adjustment process visual organ a person to different levels of brightness is commonly called brightness adaptation.

It has been experimentally shown that the range of perceived brightnesses at a given level of adaptation is very limited. All surfaces that have a brightness less than the minimum for this range appear black to us. Maximum brightness creates a sense of white. If a surface appears in the field of view, the brightness of which exceeds the maximum for this range, then the adaptation of vision will change, and the entire range of vision will correspondingly shift towards higher brightnesses. At the same time, those surfaces that, at a lower level of adaptation, seemed gray to us, will be perceived as black.

Brightness adaptation occurs as a result of a change in the brightness of the field of view, and, consequently, the illumination of the retina in the image area. Particular cases of brightness adaptation are dark And light adaptation. Dark adaptation occurs when the brightness of the field of view instantly decreases from a certain value to zero adaptation brightness. Light - with an increase in brightness from its zero value to a certain finite value. The duration of the processes of light and dark adaptation is different. While a decrease in the sensitivity of vision (light adaptation) occurs in a fraction of a second to several seconds, the process of dark adaptation lasts 60–80 minutes.

If for 10 ... 15 seconds a sheet of white paper is observed, half of which is covered with something black, and then the black is removed, then the previously closed part of the sheet will appear lighter than the rest of it. In this case, it is customary to talk about local brightness adaptation. The phenomenon of local brightness adaptation can be explained by the fact that when details of different brightness are observed simultaneously, i.e., when the illumination of different parts of the retina at the same time turns out to be different, the level of excitation of some parts affects the light sensitivity of others.

Color adaptation arises as a result of a change in the color of the field of view with its brightness unchanged. While luminance adaptation is characterized by a mismatch between lightness and brightness, color adaptation is characterized by a mismatch between the chromaticity of the radiation and the sensation of that chromaticity.

The phenomenon of color adaptation is explained by a change in the sensitivity of the eye as a result of a change in the ratio of the excitation levels of its three receivers when the eye is exposed to radiation of a certain color. Color, on

which adapts the eye, as if fading. This occurs as a result of a decrease in the sensitivity to a given color of that part of the retina that is adapted to this color. So, if after observing a green figure for 15 ... 20 seconds, look at an achromatic background, then a consistent image (a trace from the previous irritation) of a reddish color appears on the background. If you look through yellow glasses for a while, then after the glasses are removed, all surrounding objects will appear bluish. A change in color as a result of preliminary action on the eye of other colors is called consistent color contrast. It has been experimentally shown that changes in the perception of color in the process of color adaptation can be quite large, and the nature of the change in color does not depend on the brightness of the observed color.

Depending on the presence of details of different colors in the field of view, changes in visual contrasts can occur both due to a change in lightness and due to a change in color. Details considered on dark background, brighten, and on light - darken. So, two pieces of the same paper, placed in one case on black velvet, and in the other on white cloth, seem to be unequal in lightness. The lightness of the detail under the influence of the background color changes regardless of whether the background and the detail considered on it are achromatic or colored.

By placing pieces of the same gray paper on backgrounds of different colors, we note that these pieces will appear to us as different in color tone. On a red background, the gray field will acquire a greenish tint, on a blue one - yellowish, and on a green - reddish. Similar phenomenon is also observed if pieces of paper of colors different from the background color are placed on colored backgrounds: yellow on red will seem slightly greenish, yellow on green - orange, etc. This phenomenon, in contrast to sequential contrast, is called simultaneous color contrast.

It is known that the same sheet of white paper is perceived as "white" in any lighting conditions: by candlelight, by incandescent lamps and by daylight. Although the differences in the spectral composition of "white" light sometimes exceed the differences in the spectral reflectance curves of most objects, the eye almost always accurately determines the colors of objects. So, for example, although surfaces that are blue in daylight conditions turn out to be greenish when illuminated by incandescent lamps, a person continues to consider them blue. This is explained by the fact that in any lighting conditions, white details are most easily recognized, since they are always the lightest. All other colors are evaluated by the eye in relation to them. In other words, when observing a certain scene containing a number of colored objects, under certain lighting conditions, the relative sensitivities of the three eye receivers change in such a way that the ratio of their excitation levels in that part of the retina where the image of the brightest object of the scene turned out becomes equal to the ratio of excitation levels, sensational white. This phenomenon is called the phenomenon color constancy, or corrections for lighting. This phenomenon explains, for example, the fact that the viewer, when watching movies (in a darkened room), does not notice

Light perception is the ability visual analyzer to perceive light and to distinguish the degrees of its brightness. In the study of light perception, the ability to distinguish between minimal light irritation - the threshold of irritation - and to capture the smallest difference in the intensity of illumination - the threshold of discrimination.

The process of adapting the eye to different conditions lighting is called adaptation. There are two types of adaptation: adaptation to darkness when the light level decreases and adaptation to light when the light level increases.

Everyone knows how helpless you feel when you get from a brightly lit room into a dark one. Distinguishing poorly lit objects begins only after 8-10 minutes, and in order to orientate freely enough, it takes at least another 20 minutes until visual sensitivity in the dark reaches the degree necessary for this. With dark adaptation, sensitivity to light increases, the maximum adaptation is observed after an hour.

The reverse process of adaptation to high level illumination proceeds much faster than dark adaptation. When adapting to light, the sensitivity of the eye to a light stimulus decreases, it lasts about 1 minute. Upon leaving a dark room, visual discomfort disappears after 3-5 minutes. In the first case, scotopic vision is manifested in the process of dark adaptation, in the second case, photopic vision is manifested during light adaptation.

The visual system responds adequately to both fast and slow changes in radiant energy. Moreover, it is characterized by an almost instantaneous reaction to a rapidly changing environment. The light sensitivity of the visual analyzer is as variable as the characteristics of the light stimuli of the world around us. The need to adequately perceive the energy of both very weak and very strong light sources, without being subjected to structural damage, is ensured by the ability to rearrange the mode of operation of the receptors. In the bright light light sensitivity of the eye is reduced, but at the same time, the reaction to the spatial and temporal differentiation of objects is aggravated. In the dark, the whole process is reversed. This complex of changes in both light sensitivity and resolving power of the eye depending on the external (background) illumination is called visual adaptation.

The scotopically adapted retina is maximally sensitive to the light energy of the low level, but at the same time its spatial resolution sharply decreases and color perception disappears. The photopic-adapted retina, being low-sensitive to distinguish between weak light sources, at the same time has a high spatial and temporal resolution, as well as color perception. For these reasons, even on a cloudless day, the moon fades and the stars go out, and at night, without highlighting, we lose the ability to read text even in large print.

The range of illumination within which visual adaptation is carried out is enormous; in quantitative terms, it is measured from a billion to several units.

Retinal receptors are very high sensitivity- they can be irritated by one quantum of visible light. This is due to the action of the biological law of amplification, when, after the activation of one molecule of rhodopsin, hundreds of its molecules are activated. In addition, retinal rods are organized into large functional units in low light. Impulse from a large number rods converges into bipolar and then into ganglion cells, causing an amplifying effect.

As the illumination of the retina increases, vision, determined mainly by the rod apparatus, is replaced by cone vision, and the maximum sensitivity shifts in the direction from the short-wavelength to the long-wavelength part of the spectrum. This phenomenon, described by Purkinje as early as the 19th century, is well illustrated by everyday observations. In a bouquet of wild flowers on a sunny day, yellow and red poppies stand out, at dusk - blue cornflowers (shift of the maximum sensitivity from 555 to 519 nm).

To distinguish colors crucial has their brightness. The adaptation of the eye to different levels of brightness is called adaptation. There are light and dark adaptations.

Light adaptation means a decrease in the sensitivity of the eye to light in conditions of high illumination. With light adaptation, the cone apparatus of the retina functions. Practically, light adaptation occurs in 1–4 min. The total time of light adaptation is 20-30 minutes.

Dark adaptation- this is an increase in the sensitivity of the eye to light in low light conditions. With dark adaptation, the rod apparatus of the retina functions.

At brightnesses from 10-3 to 1 cd / m 2, teamwork rods and cones. This so-called twilight vision.

Color adaptation involves a change in color characteristics under the influence of chromatic adaptation. This term refers to the decrease in the sensitivity of the eye to color with more or less prolonged observation of it.

4.3. Patterns of color induction

color induction- this is a change in the characteristics of a color under the influence of the observation of another color, or, more simply, the mutual influence of colors. Color induction is the eye's desire for unity and wholeness, for the closing of the color circle, which in turn serves as a sure sign of a person's desire to merge with the world in all its integrity.

At negative induction characteristics of two mutually inducing colors change in the opposite direction.

At positive Induction, the characteristics of the colors converge, they are "trimmed", leveled.

Simultaneous induction is observed in any color composition when comparing different color spots.

Consistent induction can be observed by simple experience. If you put a colored square (20x20 mm) on White background and fix your eyes on it for half a minute, then on a white background we will see a color that contrasts with the color of the paint (square).

Chromatic induction is a change in the color of any spot on a chromatic background in comparison with the color of the same spot on a white background.

Luminosity induction. With a large contrast in brightness, the phenomenon of chromatic induction is significantly weakened. The smaller the difference in brightness between two colors, the stronger the perception of these colors is affected by their color tone.

Basic patterns of negative color induction.

The measure of induction staining is affected by the following factors.

Distance between spots. The smaller the distance between the spots, the greater the contrast. This explains the phenomenon of edge contrast - an apparent change in color towards the edge of the spot.

Contour clarity. A clear contour increases luminance contrast and reduces chromatic contrast.

The ratio of the brightness of color spots. The closer the brightness values of the spots, the stronger the chromatic induction. Conversely, an increase in brightness contrast leads to a decrease in chromaticity.

Spot area ratio. The larger the area of one spot relative to the area of another, the stronger its induction effect.

Spot saturation. The saturation of the spot is proportional to its inductive action.

observation time. With prolonged fixation of spots, the contrast decreases and may even disappear altogether. Induction is best perceived with a quick glance.

The area of the retina that fixes color spots. Peripheral areas of the retina are more sensitive to induction than the central one. Therefore, the ratios of colors are more accurately estimated if you look somewhat away from the place of their contact.

In practice, the problem often arises weaken or eliminate induction staining. This can be achieved in the following ways:

mixing the background color into the spot color;

circling the spot with a clear dark outline;

generalization of the silhouette of spots, reduction of their perimeter;

mutual removal of spots in space.

Negative induction can be caused by the following reasons:

local adaptation- a decrease in the sensitivity of a part of the retina to a fixed color, as a result of which the color that is observed after the first one, as it were, loses the ability to intensely excite the corresponding center;

autoinduction, i.e., the ability of the organ of vision in response to irritation with any color to produce the opposite color.

Color induction is the cause of many phenomena, united by the general term "contrasts". In scientific terminology, contrast means any difference in general, but at the same time the concept of measure is introduced. Contrast and induction are not the same, because contrast is the measure of induction.

Brightness Contrast characterized by the ratio of the difference in the brightness of the spots to the greater brightness. Brightness contrast can be large, medium and small.

Saturation Contrast characterized by the ratio of the difference in saturation values to the greater saturation . Contrast in color saturation can be large, medium and small.

Color tone contrast characterized by the size of the interval between colors in a 10-step circle. Hue contrast can be high, medium, and low.

Great Contrast:

high contrast in hue with medium and high contrast in saturation and brightness;

Medium contrast in hue with high contrast in saturation or brightness.

Average Contrast:

average contrast in hue with average contrast in saturation or brightness;

low contrast in hue with high contrast in saturation or brightness.

Small Contrast:

low contrast in hue with medium and low contrast in saturation or brightness;

medium contrast in hue with little contrast in saturation or brightness;

high contrast in hue with low contrast in saturation and brightness.

Polar contrast (diametrical) is formed when differences reach their extreme manifestations. Our sense organs function only through comparisons.

The peripheral organ of vision reacts to ongoing changes in lighting and functions regardless of the degree of brightness of the lighting. Adaptation is the ability of the eye to adapt to different levels illumination. The reaction of the pupil to the ongoing changes gives the perception of visual information in a millionth intensity range from lunar to bright lighting, despite the relative dynamic response volume of visual neurons.

Types of adaptation

Scientists have studied the following types:

light - adaptation of vision in daylight or bright light;
dark - in darkness or weak light;
color - conditions for changing the color of highlighting objects that are located around.

How is it happening?

Light adaptation

Occurs when going from dark to strong light. It instantly blinds and initially only white is visible, since the sensitivity of the receptors is set to dim light. It takes one minute for the sharp light hit cones to capture it. With habituation, the light sensitivity of the retina is lost. Full adaptation of the eye to natural light occurs within 20 minutes. There are two ways:

a sharp decrease in the sensitivity of the retina;
mesh neurons undergo rapid adaptation, inhibiting the function of the rod and favoring the cone system.

Dark adaptation

The dark process occurs during the transition from a brightly lit area to a dark one.

Dark adaptation is the reverse process of light adaptation. This happens when moving from a well-lit area to a dark area. Initially, blackness is observed as the cones cease to function in low intensity light. The adaptation mechanism can be divided into four factors:

Light Intensity and Time: By increasing the levels of pre-adapted luminances, the cone's dominance time is extended while the rod's switching is delayed.
Retinal size and location: The location of the test spot affects the dark curve due to the distribution of rods and cones in the retina.
The wavelength of the threshold light directly affects dark adaptation.
Regeneration of rhodopsin: when exposed to light photopigments, both rod and cone photoreceptor cells receive structural changes.

It is worth noting that night vision has much more low quality than vision in normal light, as it is limited to a reduced resolution and allows you to distinguish only shades of white and black. It takes about half an hour for the eye to adjust to the twilight and acquire a sensitivity hundreds of thousands of times greater than in daylight.

It takes much longer for older people to get used to the dark than for younger people.

Color adaptation

For a person, color objects change under different lighting conditions only for a short period of time.

It consists in changing the perception of retinal receptors, in which the maxima of spectral sensitivity are located in different color spectra radiation. For example, when changing natural daylight to the light of lamps in a room, changes will occur in the colors of objects: green color will be reflected in a yellow-green tint, pink - red. Such changes are visible only for a short period of time, over time they disappear and it seems that the color of the object remains the same. The eye gets used to the radiation reflected from the object and is perceived as in daylight.