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are they really all red?

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I spoke with Anders Winell in Konstfack about how light would affect the colour of the chair and we tried out this test with red, blue and green LEDs. The photos aren’t so reliable colourwise but the red makes the chair hyper-red, the green black and the blue a dark blue.

We spoke about a non-fiction book I was reading called ‘The Island of the Colour Blind’ which is about an island called Pingelap where half of the population has Achromatopsia, a condition meaning that you see only in greys. Sufferers of this condition also have reduced vision and a high sensitivity to light. They see much better in the times when light is low ie. dusk or dawn and are totally blind in full sunlight.

Anders also talked about red light and sensitivity of the eyes to red light and green and blue. It turns out that they eyes are less sensitive in red light and therefore vision is impaired in red light.

“Persons who have achromatopsia (sometimes called achromatopia) do not have normal “cone vision.” In the retinas of normal eyes there are 6 million cone photoreceptors, located mostly at the center of the retina. There are complete and incomplete forms of achromatopsia. Persons with complete achromatopsia must rely on their “rod vision.” In the normal eye there are 100 million rod photoreceptors. Rods are located mostly at the periphery of the retina. Rods “saturate” at higher levels of illumination. Therefore, the eyes of achromats, lacking normal cone vision and having only rod vision, are not able to adapt normally to higher levels of illumination. Rods do not provide color vision or good detail vision. Therefore, persons with achromatopsia are either totally colorblind or almost totally colorblind, and they have poor visual acuity. There are many variations in the severity of these manifestations among individual achromats. There are complete rod monochromats, incomplete rod monochromats, and blue cone monochromats. Complete rod monochromats have the most severely impaired vision of all achromats. Blue cone monochromacy is much rarer than rod monochromacy and has entirely different inheritance factors.”

Misdiagnosis is common. As one example, many achromats have been given the diagnosis of “congenital nystagmus.” Nystagmus (involuntary movement of the eyes) is a symptom of achromatopsia, one that is especially noticeable during infancy and childhood, but having this symptom is not the same as having the medical eye condition which is known as “congenital nystagmus.”

As levels of illumination increase, the vision of persons with achromatopsia decreases. In moderately bright indoor spaces or outdoors just after dawn or just before dusk, some achromats adapt to their reduced level of visual functioning without resorting to tinted lenses, by using visual strategies such as blinking, squinting, shielding their eyes, or positioning themselves favorably in relation to light sources. Others routinely wear medium tinted lenses in such settings. However, in full sunlight outdoors or in very bright indoor spaces, almost all achromats use very dark tinted lenses in order to function with a reasonable amount of vision, since their retinas do not possess the photoreceptors needed for seeing well in such settings.

Public awareness of achromatopsia has greatly increased in recent years as a result of the publication of Dr. Oliver Sacks’ book, The Island of the Colorblind (hardback edition, Alfred Knopf publisher; paperback edition, Vintage Press publisher — in the U.S.) and the TV documentary film, “Island of the Colorblind,” which has been shown since 1996 in the U.K. and since 1998 in the U.S. and certain parts of Canada. Dr. Sacks usually refers to achromatopsia as “achromatopia,” and he refers to a person having this vision disorder as an “achromatope.” These terms are variations of the more commonly used terms, “achromatopsia” and “achromat.”

Congenital, inherited achromatopsia should not be confused with cerebral achromatopsia, which is an acquired form of total colorblindness that can result from trauma, illness, or some other cause. Persons who develop cerebral achromatopsia report that they see a monochromatic world, all in shades of gray. They are able to see gray because they previously experienced color vision, making it possible for them to perceive the absence of color as gray. This is in sharp contrast to the visual perception of congenital, complete achromats (i.e., complete rod monochromats), who report that the concept of “gray” is as mystifying to them as is the concept of any of the other colors. Persons with cerebral achromatopsia are diagnosed by neurologists, rather than eye specialists. Their loss of color perception is not accompanied by severely impaired vision, extreme light sensitivity, or abnormality in the photoreceptors of the retina, as is the case with persons who have congenital, inherited achromatopsia.[1]

Illustrated in Figure 6 are the absorption spectra of the four human visual pigments, which display maxima in the expected red, green, and blue regions of the visible light spectrum. When all three types of cone cell are stimulated equally, the light is perceived as being achromatic or white. For example, noon sunlight appears as white light to humans, because it contains approximately equal amounts of red, green, and blue light. An excellent demonstration of the color spectrum from sunlight is the interception of the light by a glass prism, which refracts (or bends) different wavelengths to varying degrees, spreading out the light into its component colors. Human color perception is dependent upon the interaction of all receptor cells with light, and this combination results in nearly trichromic stimulation. There are shifts in color sensitivity with variations in light levels, so that blue colors look relatively brighter in dim light and red colors look brighter in bright light. This effect can be observed by pointing a flashlight onto a color print, which will result in the reds suddenly appearing much brighter and more saturated.

n recent years, consideration of human color visual sensitivity has led to changes in the long-standing practice of painting emergency vehicles, such as fire trucks and ambulances, entirely red. Although the color is intended for the vehicles to be easily seen and responded to, the wavelength distribution is not highly visible at low light levels and appears nearly black at night. The human eye is much more sensitive to yellow-green or similar hues, particularly at night, and now most new emergency vehicles are at least partially painted a vivid yellowish green or white, often retaining some red highlights in the interest of tradition.

When only one or two types of cone cells are stimulated, the range of perceived colors is limited. For example, if a narrow band of green light (540 to 550 nanometers) is used to stimulate all of the cone cells, only the ones containing green photoreceptors will respond to produce a sensation of seeing the color green. Human visual perception of primary subtractive colors, such as yellow, can arise in one of two ways. If the red and green cone cells are simultaneously stimulated with monochromatic yellow light having a wavelength of 580 nanometers, the cone cell receptors each respond almost equally because their absorption spectral overlap is approximately the same in this region of the visible light spectrum. The same color sensation can be achieved by stimulating the red and green cone cells individually with a mixture of distinct red and green wavelengths selected from regions of the receptor absorption spectra that do not have significant overlap. The result, in both cases, is simultaneous stimulation of red and green cone cells to produce a sensation of yellow color, even though the end result is achieved by two different mechanisms. The ability to perceive other colors requires the stimulation of one, two, or all three types of cone cells, to various degrees, with the appropriate wavelength palette.[2]


Written by alltheredchairs

January 27, 2012 at 6:17 pm

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