The following observation is reported here for your interest and experimentation. Comments and explanations are welcome.
I have a cut glass suncatcher which hangs in the window, suspended from a string. When the sun shines on the prism, rainbows are cast onto the wall and surrounding objects. The rainbows' colour bands are in a vertical orientation. If the prism is spun slowly, the rainbows move horizontally but still have multiple colours so look like rainbows.
Spin the prism faster, so the rainbows rapidly sweep around horizontally. Above a certain speed the moving bands of light appear to be white. After the spinning slows down, they become moving rainbows again.
Question #1: Why do the bands of light look white when the prism is spun fast?
Question #2: What is the critical speed at which this blending occurs? The transition appeared sudden for myself. Is this true for others? Is the speed dependent on the individual, and perhaps on their training - e.g. tachistoscope training for speed reading?
Presumably there is a required minimum response time for the human visual system to "recognize" a colour. If the colour at a particular spot changes faster than that required response time, one just notices a "blend" of colours - that is, white.
Question #3: If that is the case, why would not one just see a continuous horizontal strip of white, instead of moving bands?
Question #4: Would this "recognition" depend upon the time required for a chemical process in the eye, or would it depend upon the time required for some sort of processing in the brain, or both? Would this answer differ for different individuals, or under different conditions?
Question #5: What happens if one looks through a colour filter? What about sunglasses which filter out the blues and let longer wavelengths pass thru, so one still sees multiple colours but only certain ones? Are the recognition speeds dependent upon colour wavelength?
If you have gathered any data from personal experimentation, or know the answer to one of these questions, or have a comment, or want to suggest hypotheses or additional questions, please reply by electronic mail.
E-Mail: Ken Roberts ken2@mirror.org
URL:
http://www.mirror.org/ken.roberts/rainbow.blending.html
Last revised October 5, 1996 by
Ken Roberts
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