Saturday night science experiment. How the eyes see the visible spectrum.

[tridim]

Yep, I'm bored. :)

So I'm cutting some paper for an unrelated project and accidentally discover that if I look thought a slit in the paper (cut with an exacto knife) at a bright light source, at the right distance and eye focus, I can see a faint spectrum of the light. I can also see the spectral fingerprint lines of the light. Pretty freaking cool!


Not my photo, but this is basically what I see, only much fainter.

Anyway, after some testing I discovered that the spectrum I see in the left eye goes red-yellow-green-blue-purple, left-to-right and the right eye sees the exact opposite. purple-blue-green-yellow-red, left-to-right.

Assuming our retinas are the same in both eyes, why do they see the spectrum reversed? What's the purpose? Could this help us see color depth better? Is it just an optical illusion of the brain? Does our brain use this difference to keep track of which eye image is which?

Thinking about the brain is fun. -Brain

[Tunkamerica]

1. I think it depends on the blotter paper used

[tridim]

4. 15 years ago and that might have been the case.

Try it!

[Occulus]

2. Can you tell us *exactly* how to reproduce the effect?

Materials, light source, etc. I'd like to observe this myself.

[tridim]

3. Here's how I did it..

Cut slits in the paper of different widths, make the slits as small as possible. Just big enough so you can see light passing through. Hair-width is a good target. Black paper would work best, but I just used regular copy paper.

CFL desk lamp about 3 feet away, slit about 6" from my eye, other eye closed, eye in "relaxed" focus like when viewing 3D stereograms.

Move the paper around and change your focus slightly until you find the best looking spectrum. The closer the slit is to your eye, the more detail you can see. You can also manipulate the slit width slightly by pulling and pushing both ends of the paper. The spectral lines only appear when the slit is as tiny as possible.

BTW I just tested it again this morning in case I was tripping last night. Yep, still works. :)

[Occulus]

7. Cool, thanks

:D

[caraher]

5. Are you sure it really mattered which eye you used?

I'd expect that what you should see is a pattern on either side of the slit, that looks the same no matter which eye you use. The order of the colors should be different on either side of the slits but not depend on which eye.

What I think should be happening is that you are getting diffraction, and the angle of diffraction for each color depends on wavelength. So the longest wavelengths (red) deflect the most and the shortest (violet) deflect the least.

[tridim]

6. There is definitely diffraction going on

I can see it if I focus on the light source (as viewed through the slit) instead of focusing on the slit itself. The light bends at the edges. I'm pretty sure that's how all the old light/slit experiments worked.

I see the spectrum defined within the width of the slit, not outside the edges. The red side is definitely more defined, it gets really dark red right up near the edge. The UV side actually fades to black (as expected), I just didn't mention it because technically I can't see the UV part, which is why it appears black.

It definitely changes direction depending on which eye is used. What bothers me is that the same effect can't be seen when the spectrum is projected through the slit onto a wall, as was done in the old light experiments. The effect only occurs when the light is viewed directly, not projected.

Maybe it's just me? I hope someone else can verify this.