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Thread: Benham disks

  1. #1
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    May 2004
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    Benham disks

    How do these things work? I mean, I know how to work them (spin fast) but why do black and white patterns look so colorful? Did not quite understand Wikipedia's explanation.

  2. #2
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    Jul 2005
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    Thye're called Fechner Colours, which is a useful search term.
    Short wavelength retinal cone cells respond more slowly than long wavelength cones, so if you present the retina with rapidly flickering white light, you produce mismatched colour signals from the retina that don't properly balance out to a neurological white signal.
    How that mechanism plays out in detail still seems to be a matter for debate (128KB pdf).

    Grant Hutchison

  3. #3
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    Feb 2006
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    I wonder if this might be related to the effect which causes visual problems (flickering color bands along high-contrast sharp edges) for some people when DLP video projectors are used. Some people (like me) have to concentrate to even notice the projector effect. Others are made nauseous by it.
    Selden

  4. #4
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    Are the colors universal or idiosyncratic? If I see blue in one line, will someone else see red-violet, and another person lime green?

  5. #5
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    Quote Originally Posted by Tom Mazanec View Post
    Are the colors universal or idiosyncratic? If I see blue in one line, will someone else see red-violet, and another person lime green?
    Not perfectly universal, because we don't all match particular Fechner colours to the same colour chip, but not entirely idiosyncratic either, since the effect relies on underlying chemistry and physiology we largely all share.
    There's also quite a lot of within-individual variation according to things like ambient lighting, attention, fatigue ...

    Back in the 1960s the BBC's science strand Tomorrow's World made a brief colour broadcast on black and white TVs, using Fechner colours. (This was before anyone worried about flicker-induced epileptic fits.) I remember a woman's lips, supposedly wearing bright red lipstick, which I saw as a deep muddy brown. Discussion the next day suggested that a lot of people saw the intended red, but many saw a shade of brown (caused by an admixture of a green sensation). But that was the range of experience, IIRC - there were no bright blues or purples, which makes sense in terms of a largely shared physiological response.

    Grant Hutchison

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