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Scotopic
In the study of human visual perception, scotopic vision (or scotopia) is the vision of the eye under low-light conditions. The term comes from Greek ''skotos'', meaning "darkness", and ''-opia'', meaning "a condition of sight". In the human eye, cone cells are nonfunctional in low visible light. Scotopic vision is produced exclusively through rod cells, which are most sensitive to wavelengths of around 498 nm (blue-green) and are insensitive to wavelengths longer than about 640 nm (red-orange). This condition is called the Purkinje effect. Retinal circuitry Of the two types of photoreceptor cells in the retina, rods dominate scotopic vision. This is caused by increased sensitivity of the photopigment molecule expressed in rods, as opposed to that in cones. Rods signal light increments to rod bipolar cells, which, unlike most bipolar cell types, do not form direct connections with retinal ganglion cells - the output neuron of the retina. Instead, two types of amacr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesopic Vision
Mesopic vision, sometimes also called twilight vision, is a combination of photopic and scotopic vision under low-light (but not necessarily dark) conditions. Mesopic levels range approximately from 0.01 to 3.0 cd/m2 in luminance. Most nighttime outdoor and street lighting conditions are in the mesopic range. Human eyes respond to certain light levels differently. This is because under high light levels typical during daytime (photopic vision), the eye uses cones to process light. Under very low light levels, corresponding to moonless nights without artificial lighting (scotopic vision), the eye uses rods to process light. At many nighttime levels, a combination of both cones and rods supports vision. Photopic vision facilitates excellent color perception, whereas colors are barely perceptible under scotopic vision. Mesopic vision falls between these two extremes. In most nighttime environments, enough ambient light prevents true scotopic vision. In the words of Duco ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Purkinje Effect
The Purkinje effect (; sometimes called the Purkinje shift, often incorrectly pronounced ) is the tendency for the peak luminance sensitivity of the eye to shift toward the blue end of the color spectrum at low illumination levels as part of dark adaptation. In consequence, reds will appear darker relative to other colors as light levels decrease. The effect is named after the Czech anatomist Jan Evangelista Purkyně. While the effect is often described from the perspective of the human eye, it is well established in a number of animals under the same name to describe the general shifting of spectral sensitivity due to pooling of rod and cone output signals as a part of dark/light adaptation. This effect introduces a difference in color contrast under different levels of illumination. For instance, in bright sunlight, geranium flowers appear bright red against the dull green of their leaves, or adjacent blue flowers, but in the same scene viewed at dusk, the contrast is re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photopic Vision
Photopic vision is the vision of the eye under well-lit conditions ( luminance levels from 10 to 108 cd/m2). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher visual acuity and temporal resolution than available with scotopic vision. The human eye uses three types of cones to sense light in three bands of color. The biological pigments of the cones have maximum absorption values at wavelengths of about 420 nm (blue), 534 nm (bluish-green), and 564 nm (yellowish-green). Their sensitivity ranges overlap to provide vision throughout the visible spectrum. The maximum efficacy is 683 lm/W at a wavelength of 555 nm (green). By definition, light at a frequency of hertz has a luminous efficacy of 683 lm/W. The wavelengths for when a person is in photopic vary with the intensity of light. For the blue-green region (500 nm), 50% of the light reaches the image point of the ret ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Candela
The candela ( or ; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous to radiant intensity, but instead of simply adding up the contributions of every wavelength of light in the source's spectrum, the contribution of each wavelength is weighted by the standard luminosity function (a model of the sensitivity of the human eye to different wavelengths). A common wax candle emits light with a luminous intensity of roughly one candela. If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not obscured. The word ''candela'' is Latin for ''candle''. The old name "candle" is still sometimes used, as in '' foot-candle'' and the modern definition of '' candlepower''. Definition The 26th General Conference on Weights and Meas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhodopsin
Rhodopsin, also known as visual purple, is a protein encoded by the RHO gene and a G-protein-coupled receptor (GPCR). It is the opsin of the rod cells in the retina and a light-sensitive receptor protein that triggers visual phototransduction in rods. Rhodopsin mediates dim light vision and thus is extremely sensitive to light. When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is regenerated fully in about 30 minutes, after which the rods are more sensitive. Defects in the rhodopsin gene cause eye diseases such as retinitis pigmentosa and congenital stationary night blindness. Names Rhodopsin was discovered by Franz Christian Boll in 1876. The name rhodospsin derives from Ancient Greek () for "rose", due to its pinkish color, and () for "sight". It was coined in 1878 by the German physiologist Wilhelm Friedrich Kühne (1837-1900). When George Wald discovered that rhodopsin is a holoprotein, consisting of retinal and an apoprotein, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photopic Lux
Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 108 cd/m2). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher visual acuity and temporal resolution than available with scotopic vision. The human eye uses three types of cones to sense light in three bands of color. The biological pigments of the cones have maximum absorption values at wavelengths of about 420 nm (blue), 534 nm (bluish-green), and 564 nm (yellowish-green). Their sensitivity ranges overlap to provide vision throughout the visible spectrum. The maximum efficacy is 683 lm/W at a wavelength of 555 nm (green). By definition, light at a frequency of hertz has a luminous efficacy of 683 lm/W. The wavelengths for when a person is in photopic vary with the intensity of light. For the blue-green region (500 nm), 50% of the light reaches the image point of the retina. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amacrine Cell
Amacrine cells are interneurons in the retina. They are named from the Greek roots ''a–'' ("non"), ''makr–'' ("long") and ''in–'' ("fiber"), because of their short neuronal processes. Amacrine cells are inhibitory neurons, and they project their dendritic arbors onto the inner plexiform layer (IPL), they interact with retinal ganglion cells and/or bipolar cells. Structure Amacrine cells operate at inner plexiform layer (IPL), the second synaptic retinal layer where bipolar cells and retinal ganglion cells form synapses. There are at least 33 different subtypes of amacrine cells based just on their dendrite morphology and stratification. Like horizontal cells, amacrine cells work laterally, but whereas horizontal cells are connected to the output of rod and cone cells, amacrine cells affect the output from bipolar cells, and are often more specialized. Each type of amacrine cell releases one or several neurotransmitters where it connects with other cells. They are of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera. The neural retina consists of several layers of neurons interconnected by synapses and is supported by an outer layer of pigmented epithelial cells. The primary light-sensing cells in the retina are the photoreceptor cells, which are of two types: rods and cones. Rods function mainly in dim light and provide monochromatic vision. Cones function in well-lit conditions and are responsible for the perception of colour through the use of a range of opsins, as well as high-acuity vision used f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visual Acuity
Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal image within the eye, (2) the health and functioning of the retina, and (3) the sensitivity of the interpretative faculty of the brain. The most commonly referred visual acuity is the far acuity (e.g. 6/6 or 20/20 acuity), which describes the examinee's ability to recognize small details at a far distance, and is relevant to people with myopia; however, for people with hyperopia, the near acuity is used instead to describe the examinee's ability to recognize small details at a near distance. A common cause of low visual acuity is refractive error (ametropia), errors in how the light is refracted in the eyeball, and errors in how the retinal image is interpreted by the brain. The latter is the primary cause for low vision in people with a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoreceptor Cell
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation) into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential. There are currently three known types of photoreceptor cells in mammalian eyes: rods, cones, and intrinsically photosensitive retinal ganglion cells. The two classic photoreceptor cells are rods and cones, each contributing information used by the visual system to form an image of the environment, sight. Rods primarily mediate scotopic vision (dim conditions) whereas cones primarily mediate to photopic vision (bright conditions), but the processes in each that supports phototransduction is similar. A third class of mammalian photoreceptor cell was disc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rod Cell
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 92 million rod cells (vs ~6 million cones) in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is the main reason why colors are much less apparent in dim light. Structure Rods are a little longer and leaner than cones but have the same basic structure. Opsin-containing disks lie at the end of the cell adjacent to the retinal pigment epithelium, which in turn is attached to the inside of the eye. The stacked-disc structure of the detector portion of the cell allows for very high efficiency. Rods are much more common than cones, with about 120 million rod cells com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deilephila Elpenor
Deilephila elpenor, the elephant hawk moth or large elephant hawk moth, is a moth in the family Sphingidae. Its common name is derived from the caterpillar's resemblance to an elephant's trunk. It is most common in central Europe and is distributed throughout the Palearctic region. It has also been introduced in British Columbia, Canada. Its distinct olive and pink colouring makes it one of the most recognisable moths in its range. However, it is quite easy to confuse the elephant hawk moth with the small elephant hawk moth, a closely related species that also shares the characteristic colours. These moths are nocturnal and therefore feed on flowers that open or produce nectar at nighttime. The elephant hawk moth has very sensitive eyes that allow it to see colour even at low-light, and it was one of the first species in which nocturnal colour vision was documented in animals. The moth is also known for its hovering capability, which it utilises when feeding on nectar from flower ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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