2 comments on “Chromatic Flicker

  1. What do you mean by “as we follow one blade”? I’m still having trouble understanding what’s going on because I don’t understand the significance of the blades being in motion. If I’m looking straight down at a spinning fan, and the fluorescent tube is above my head, don’t the blue or orange glows (photons) all hit each blade at the same time, and bounce back into my eye at the same time?

  2. So the fluorescent light is going blue-red-blue at 120 Hz. The fan is revolving at 60 Hz. Let’s imagine in slow motion. Also remember that light travels fast enough that we can just assume the color of the light is everywhere at once. We start with the blade is at 12 o’clock and the light being blue. 1/240 seconds pass and the blade is now at 3 o’clock and the color has moved from blue to red. Another 1/240 seconds pass and the blade is now at 6 o’clock and the light is blue again. Another 1/240 seconds pass and the blade is now at 9 o’clock and the light is red. Another 1/240 seconds pass, completing a cycle, and the blade is back at 12 o’clock and the light is blue. A human can’t see that happen, but it did, and the result is blue coloring at 12 and 6 o’clock and red coloring at 3 and 9 o’clock, and gradients in between. The opposite blade tells a similar story, starting a 6 o’clock instead, but its color as a function of position marries up with the first blade’s. You know the blades always appear the same color at the same time. The color as a function of position marries up as long as the color pattern repeats an even number of times around one revolution. Running the fan at 120 Hz would mean blade 1 creates blue at 12 o’clock and red at 6 o’clock, while blade 2 creates blue at 6 o’clock and red at 12 o’clock. The two patterns would more or less cancel out in terms of perceived color, but you might still see a variation in intensity.

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