The conditions were horrible, the visibility poor, but the traffic was light.I saw nothing of the scenery visibility was down to fifty yards.Fog has reduced visibility to under 20 metres.Poor visibility made skiing extremely hazardous.Radio and television commentators suggested it occurred because of poor visibility in the rain and fog along the border.Planes must have at least a half-mile of visibility to land.The advantage of coupons is that they give products high visibility.Large umbrellas offer high visibility and are often branded.The article in the paper meant good visibility for the company.Conditions are perfect for the yacht race there is a light wind and visibility is good.3 SEE the fact of being easy to see high visibility clothing Examples from the Corpus visibility 2 the situation of being noticed by people in general visibility of The exhibition helped increase the visibility of women artists. good/poor visibility The search for survivors was abandoned because of poor visibility. ○○ AWL noun 1 DN the distance it is possible to see, especially when this is affected by weather conditions Visibility on the roads is down to 20 metres due to heavy fog.In day blindness, or total color blindness, the cones do not function and therefore there is only a curve for rod vision.Visibly ≠ invisibly From Longman Dictionary of Contemporary English Related topics: Nature visibility vis‧i‧bil‧i‧ty / ˌvɪzəˈbɪləti / People with hemeralopia ( night blindness) show no rod curve at all only the cones are operative. These shapes come to us in various shades of gray, according to the visibility curve of the rods for different wavelengths.Visibility curves can be used in diagnosing certain visual defects. There is usually enough light energy at night to enable us to see the shapes of the flowers in the garden even though we cannot see the colors. Tfie eye is actually more rather than less sensitive in darkness than in light, since less light is required to activate the rods than the cones. This explains why blues and greens appear especially bright in twilight.Studies of retinal sensitivity also help to explain dark adaptation. The resulting curve, known as the scotopic or darkness vision curve, shows maximal sensitivity at 510 millimicrons, a portion of the spectrum that corresponds to bluish-green, even though the colors themselves are visible only as shades of gray. The curve for rod vision is obtained by making the test patch of light fall on the periphery of the retina, which contains all rods and no cones. The resulting curve, called a photopic (daylight) visibility curve, shows that the retina is most sensitive to greenish-yellow light, which has a wavelength of approximately 555 millimicrons. This point is called the absolute threshold, and the curve shows these thresholds for all visible wavelengths.The curve for cone vision is obtained by exposing the light patch so that it falls on the fovea of the eye, a small area of the retina that contains only cones and no rods. One method of obtaining these curves is to expose the eyes to test patches of various wavelengths, and in each case to increase the intensity of the patch from zero until the subject indicates that he sees it. The daylight visibility curve therefore represents cone vision and the night visibility curve represents rod vision. This shift in the relative brightness of colors in low illumination is called the Purkinje effect, named after the Bohemian physiologist who first studied it.The Purkinje effect occurs because the retina contains different cells for color (cone cells) and for brightness (rod cells), and in decreasing illumination the eye shifts from cone to rod functioning. The leaves of a rose bush look bright long after the roses have turned to black, and by nightfall no colors at all are visible. As twilight comes on, these colors darken and the greens and blues begin to stand out. During daylight we register all the colors in a variegated garden, with the yellows and reds appearing particularly bright. See visible spectrum.Our eyes are not equally sensitive to all types of light. They are sometimes said to measure “ spectral sensitivity,” since they cover the range of wavelengths which make up the visible spectrum. Two types of curves are usually constructed, one for daylight vision and the other for night vision. A graph representing the sensitivity of the eye to different wavelengths of light.
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