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Color Blindness

One of my best friends has a color vision deficiency, or “color blindness,” as it is also known.  Being as that we are best of friends, I have asked him on several occasions to describe what he sees as I compare it to what I see when looking at things like posters, movies, the sky, and other colorful things so I could get a sense of how our vision was different.  He’s also the first to poke fun at himself when he shows up somewhere in purple pants and an orange sweater, or something as equally hilarious as that.  “I had no idea, because, you know, I CAN’T SEE THOSE COLORS!”

The condition my friend has is called Protanopia, or basically a complete lack of red photoreceptors in the retina.  Red hues appear black or dark; it is hereditary, sex-linked, and present in 1% of all males, according to Wikipedia’s article on color blindness.  Protanopia is a form of Dichromatism – this is what occurs when one of the cone pigments of the retina, and color vision is reduced to two dimensions.

I’ve often asked him if it’s weird not being able to see a certain spectrum of colors, to which he often responds with “I have no idea, I’ve never been able to see that color, so how would I know?”  I always feel pretty ridiculous after I ask him that.

One of the most important aspects to know about color blindness is that people with color vision impairment don’t “confuse” colors or swap them in their mind – like “red is green,” “blue is yellow,” etc.  Most people exhibiting color vision impairment learn to tell colors apart by their placement or location (like a traffic lights) or textures (like camouflage).

Look at the differences in colors as seen by people with differing forms of color vision impairment:

As seen by a person with normal color vision:

The same flag, as seen by someone with Protanopia (no red receptors):

Same flag again, but this time seen by someone with Deuteranopia (no green receptors):

Same flag once more, this time as seen by someone with Tritanopia (no blue receptors).  Tritanopiais very rare:

The website Vischeck (http://www.vischeck.com/) can simulate color deficiencies on images that you upload- it’s an interesting foray into color vision deficiency.  Check it out.

The Purkinje Effect

the_eye

When I teach beginning lighting design classes, I always have a week of learning about the eye – how your rods and cones balance each other, what their respective jobs are, how the images you see are translated to the brain, and how, as lighting designers, we can use the strengths and weaknesses of the eye to heighten the audience’s experience.  Physiology always comes into play when you’re designing a lighted environment, and students always seem to enjoy finding out what different colors of light do to the body – blues are soothing (even to both genders), reds increase blood pressure and respiration rate, yellows make your eyes tire faster, and black is a submissive color.  None of the really “alternative” students appreciate being told that their black fingernails, eyeliner, and dyed hair color are really signs of compliance.

Inevitably, a question that comes up is “why do we see blue and gray at dusk and when the sun is setting?”  It’s a great question, especially because it lends itself to explanation of the photopic (lots of light, optimal conditions) and scotopic (low light, monochromatic) vision systems, and how rods and cones operate and cooperate.

The Purkinje Effect, as it’s called, is when the sun goes down, and we see a whole lot of blued out and grayed out colors.  This happens primarily at dusk, and in very low light conditions, where the color receptors (cones) basically leave it to the light receptors (rods) for detail for the brain.  When the light goes down, the color information is lacking, so the rods have to compensate.  Our vision becomes monochromatic because our color receptors, which do not interpret intensity information and respond best to yellow-ish light pass the workload on to the light receptors, which respond best to green/blue light and allow us to see shape and contrast.  Just without color.

There’s the lecture for the day.