Illusory Spectrum

Published 5 years, 8 months ago

I know, I know, this is undoubtedly a widely known optical illusion, but I had to create and share my own version after stumbling across it in the wild.  Watch the animation cycle through all four frames, 2.5 seconds per frame.  Notice anything different about the spectrum when it flips from green as opposed to when it flips from gray?

Wild!

The spectrum and greenish frames image are derived from Project Octant Part 13: Bug Hunt, which is where I saw this effect thanks to the Page Up key and the browser window being just the right height.  I hope Shamus won’t be too irked that I swiped copies to repurpose here.


  1. I don’t notice any difference. What effect do you experience?

  2. Same here, I’m not seeing any difference. I know I probably should, but I have been staring at this for 5 minutes and still nothing.

    Also, I have never heard of this optical illusion. Again, I probably should have…

    What should we see?

  3. For me, the post-green spectrum looks like it’s “zooming in” towards the green portion of the spectrum. Not the best way to put it, maybe, but I can’t think of another way to describe it. Post-gray, I don’t get that impression; it just pops into place.

  4. Sometimes I think I see a slight effect where the block appears to lengthen slightly, which has a similar effect of the green “zooming”. But it is slight and doesn’t happen every time. Not sure if I’m just looking for something because I’m told to expect something.

  5. I see the grey as ultra violet colours where the last green bit was which change out and then fade to grey. Must be the brain making assumptions on colour a bit like compression of images then re adjusting as it recognises the grey….

  6. I didn’t notice anything. But now you mention the effect I’m ‘supposed’ to see I can’t not see it! Damn you sub-conscious! I covered all but the red end of the spectrum and it still did it. After I covered all but the blue end it didn’t do it.

    Now I’m going to go and do something else for a few hours, and then come back and see if I still see the illusion.

  7. Great. Now I see it after both the green and the grey. I’m a strange individual I guess. ^_^

  8. I actually thought the trick was that after viewing the green, the spectrum looked more desaturated. Did anyone notice that?

  9. I thought the same as Andrew.

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