Found something odd while procrastinating, fan/computer

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Discussion Overview

The discussion revolves around an observation made while using a hand-crank fan directed at a computer monitor, where the fan blades appeared to change color and rotate in the opposite direction at certain speeds. Participants explore the underlying causes of this phenomenon, considering aspects of visual perception and the interaction between the fan's motion and the monitor's refresh rate.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that the observed effect is a stroboscopic effect, similar to how wheels on a stagecoach appear to move backward in films.
  • Another participant questions the origin of the blue and yellow colors observed, noting the saturation of computer light and the role of polarizing filters.
  • A different participant introduces the idea of a psycho-optic illusion, referencing a demonstration involving a spinning cylinder with alternating black and white stripes that appears colored under certain conditions, possibly involving a strobe light.
  • Another participant humorously refers to the phenomenon as the "Get Back To Work Ya Bum" effect, indicating a light-hearted take on the discussion.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the cause of the observed effects, with no consensus reached on the specific mechanisms involved or the nature of the colors seen.

Contextual Notes

Participants mention various visual phenomena and illusions without fully resolving the underlying assumptions or definitions related to the refresh rate of monitors and the perception of color.

Rainbrew
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So while not doing what I should be I was cooling myself off with this tiny fan with a hand-crank. For some odd reason I decided to point it at my monitor and make it go in reverse and noticed that at a certain speed the blades of the fan appeared to be blue and yellow and rotating in the opposite direction of the actual rotation of the fan. What causes this to occur? I assume it has something to do with the refresh rate of my monitor but I'm clueless as to why this happens. Thanks in advance!
 
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It must be a stroboscopic effect, like in the movies when the wheels of the stage coach seem to be moving backwards.
 
Chestermiller said:
It must be a stroboscopic effect, like in the movies when the wheels of the stage coach seem to be moving backwards.
What about the colours? I understand that computer light is naturally heavily saturated with blue, however the polarising filter gets rid of most of that light, so where does the blue and yellow come from?
 
Rainbrew said:
What about the colours? I understand that computer light is naturally heavily saturated with blue, however the polarising filter gets rid of most of that light, so where does the blue and yellow come from?
The refresh rate must be different for the different colors.
 
It's a psycho-optic illusion. I don't recall its name so I can't find a reference to it. If I remember the demonstration, it includes a cylinder with alternating black and white stripes on its surface, parallel with the cylinder axis. The cylinder is spinning w/ axis vertical. I think there was also a strobe light involved. The illusion was that the black and white stripes were seen as colored stripes.

I also seem to recall a similar effect with a spinning disk with either radial or spiral lines on it to create color. I think there was a strobe involved here also.
 
I think it's called the GBTWYB effect.

Get Back To Work Ya Bum.
 
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