On a clear morning, light comes through this window (viewed from the inside)

It then hits the door on the opposite side (so viewing from the outside the door straight on the other side)

There is nothing particularly special going on.

However, if I go through the door and turn around to face the door, I see this

Light seems to be dispersing into the color spectrum solely because of the hole in the wooden door. Some days it's even clearer than it is today.

What gives? I know light can do this through prisms, but how come it's happening with only a hole in a door?


Edit

As per Floris' instruction, I did a little more experimenting. Here are the results

It's far from perfect because I made the hole using a black gym bag and some masking tape, and used a handheld mirror to reflect it onto the door, but I think it shows his explanation to be correct pretty well!

  • Can you place a mirror at the point where blurry image was formed? If possible click a photo and upload it. – Immortal Player Sep 30 '14 at 13:58
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    A natural pin-hole camera, beautiful. – Adsy Sep 30 '14 at 14:55
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    If you are going to do some follow-up photography, you could cover the hole with a black piece of paper with a smaller hole in it; you will see the image resolved more clearly (although it will be darker, so you may need to put your camera on a tripod). With a piece of white paper to project onto things will be even clearer. Would be an awesome update to the question (and nice confirmation of the answer...) – Floris Sep 30 '14 at 16:13
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    @Floris I updated to show the results of a little more experimenting :) – Zach Saucier Sep 30 '14 at 20:41
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    That's great - you can even see the red and white cars! – Floris Sep 30 '14 at 20:49
up vote 116 down vote accepted

You have created a rather poor pinhole camera (camera obscura). You can see an "image" of the sky, a green space (trees) and even a reddish brown blur that is your driveway.

This is not diffraction or refraction - it's geometrical (classical) optics. Because the hole is pretty big, you see a very blurry image. But basically, the light from the sky falling through the hole hits one part of the door; the light from the trees hits a slightly different part; and the light from the driveway (the lowest object on the outside) hits the highest part on the inside, after coming through the hole.

enter image description here

Incidentally - if you took a picture from the perspective of the hole in the door, I am guessing you would see more of the sky - in your photo of the view, the sky is barely visible, but in the doorhole image it's much more prominent; and conversely, one sees less of the driveway. This is consistent with the photo being taken from a different vantage point.

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    @t.c indeed - the hole is much too big for diffraction. – Floris Sep 30 '14 at 13:49
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    I suppose I was thinking about my physics lectures on light diffraction too much, preventing me from thinking of a more simple principle. Thanks for the help! – Zach Saucier Sep 30 '14 at 13:52
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    @ZachSaucier - this happens all the time: ideas we use a lot (or have recently been exposed to) seem to show up in all kinds of places. The doctor that learns about a new disease suddenly "realizes" that lots of his patients have it... etc. This is normal. For me these puzzles are fun. You're welcome. – Floris Sep 30 '14 at 13:56
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    Good explanation. One can read more on pinhole cameras and camera obscuras on Wikipedia and elsewhere. – Jeppe Stig Nielsen Sep 30 '14 at 15:18
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    +1 Though instead of OP having created a poor pinhole camera, I'd say rather that his house has created a pretty good one, as far as pinhole cameras accidentally created by houses go. – iamnotmaynard Sep 30 '14 at 15:58

protected by Qmechanic Jan 28 '15 at 23:10

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