Video 70.wmv

• Report rights infringement
• published: 28 Dec 2009
• views: 559

pupillary light reflex is a reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retina of the eye. Greater intensity light causes the pupil to become smaller (allowing less light in), whereas lower intensity light causes the pupil to become larger (allowing more light in). Thus, the pupillary light reflex regulates the intensity of light entering the eye.[1] The retinas in the eyes have receptors for color called cones. You have one that measures the amount red light, another measures green light, and the third measures light intensity. Your occipital lobes in your brain actually process this information as color by deducing the amount of blue light from the other three factorsThe insensitivity of rods to long-wavelength light is related to the use of red lights under certain special circumstances for example, in the control rooms of submarines, in research laboratories, or during naked-eye astronomy.The effect occurs because the color-sensitive cones in the retina are most sensitive to yellow light, whereas the rods, which are more light-sensitive (and thus more important in low light) but which do not distinguish colors, respond best to green-blue light.[4] This is why we become virtually color-blind under low levels of illumination, for instance moonlight. The Purkinje effect occurs at the transition between primary use of the photopic (cone-based) and scotopic (rod-based) systems, that is, in the mesopic state: as intensity dims, the rods take over, and before color disappears completely, it shifts towards the rods' top sensitivity.Under conditions where it is desirable to have both the photopic and scotopic systems active, red lights provide a solution. Submarines are dimly lit to preserve the night vision of the crew members working there, but the control room must be lit to allow crew members to read instrument panels. By using red lights, or wearing red goggles, the cones can receive enough light to provide photopic vision (namely the high-acuity vision required for reading. Because the rods are not saturated by bright light and are not sensitive to long-wavelength red light, however, the crew member remains dark adapted, in case they need to look out the periscope at night, for exampleIsaac Newton discovered that white light is split into its component colors when passed through a prism, but that if those bands of colored light are passed through another and rejoined, they make a white beam. The characteristic colors are, in order from short to long wavelength: violet, blue, green, yellow, orange, red. Sufficient differences in wavelength give rise to a difference in perceived hue; the just noticeable difference in wavelength varies from about 1 nm in the blue-green and yellow wavelengths, to 10 nm and more in the red and blue. Though the eye can distinguish up to a few hundred hues, when those pure spectral colors are mixed together or diluted with white light, the number of distinguishable chromaticities can be quite high. In very low light levels, vision is scotopic, meaning mediated by rod cells, and not detecting color differences; the rods are maximally sensitive to wavelengths near 500 nm. In brighter light, such as daylight, vision is photopic, in which case the cone cells of the retina mediate color perception, and the rods are essentially saturated; in this region, the eye is most sensitive to wavelengths near 555 nm. Between these regions is known as mesopic vision, in which case both rods and cones are providing meaningful signal to the retinal ganglion cells. The shift in color perception across these light levels gives rise to differences known as the Purkinje effect. The perception of "white" is formed by the entire spectrum of visible light, or by mixing colors of just a few wavelengths, such as red, green, and blue, or even by mixing just a pair of complementary colors such as blue and yellow.[3] The effect occurs because the color-sensitive cones in the retina are most sensitive to yellow light, whereas the rods, which are more light-sensitive (and thus more important in low light) but which do not distinguish colors, respond best to green-blue light.[4] This is why we become virtually color-blind under low levels of illumination, for instance moonlight. The Purkinje effect occurs at the transition between primary use of the photopic (cone-based) and scotopic (rod-based) systems, that is, in the mesopic state: as intensity dims, the rods take over, and before color disappears completely, it shifts towards the rods' top sensitivity. they have led lights in thier rings earrings watches even tounge rings and piercings the left eye is affected cuasing unbalance and hindering breathing