Diffraction Patterns

[Ironbeard]

Often when my curtains are closed with perhaps a few millimetres of space between them, I see a trianglular pattern of light on the ceiling and a series of parallel vertical lines projected on the opposite wall. Is this a diffraction pattern? It seems unlikely that a phenomenon which was studied comparitively recently in the history of optics and is recreated with specialised equipment (lasers and extremely narrow slits) in undergraduate laboratories can be reproduced so simply.

[Admiral Valdemar]

Often when my curtains are closed with perhaps a few millimetres of space between them, I see a trianglular pattern of light on the ceiling and a series of parallel vertical lines projected on the opposite wall. Is this a diffraction pattern? It seems unlikely that a phenomenon which was studied comparitively recently in the history of optics and is recreated with specialised equipment (lasers and extremely narrow slits) in undergraduate laboratories can be reproduced so simply.

Possibly, diffraction patterns happen when the light wavelength is matched by a slit of equal size, IIRC.

That or it's just another optical effect.

[Einhander Sn0m4n]

They're probly moire patterns. They're very common when you get two or more repating line patterns superimposed on each other.

[kojikun]

Ironbird, you're lucky to be witnessing naturally what appears to be one of the oldest proofs of quantum mechanics known to man. You're seeing interference patterns, i believe, created by the wave-nature of light.

Pretty cool that this happens naturally for you, usually it takes a few opaque sheets with holes, or a laser and one opaque sheet.

[kojikun]

Possibly, diffraction patterns happen when the light wavelength is matched by a slit of equal size, IIRC.

Can't be, millimetre wavelength is well into the microwave range, while visible light is always smaller then about 670 NANOmetres.

[Admiral Valdemar]

Possibly, diffraction patterns happen when the light wavelength is matched by a slit of equal size, IIRC.

Can't be, millimetre wavelength is well into the microwave range, while visible light is always smaller then about 670 NANOmetres.

I have no idea what the curtains are like, they could be razors for all I know.

[Ironbeard]

Okay, according to my physics textbook, sin(theta)=m(lambda)/u where theta is the angle between a dark fringe and the normal, m is an integer, lambda is the wavelength and u is the slit size. Given that the gap is several thousand times the wavelength and the dimensions of my room are such that angles of up to 30 degrees are involved, it doesn't look like I'm seeing diffraction patterns. Also, I don't see any kind of spectrum - there I go, posting about what it superficially looks like without any real thought.

I'm still curious as to what it is, though. The pattern I see projected on my cieling is more trapezoidal than triangular, although it does seem to project back to the gap in the curtains. Definite streaks of light and dark are observed on the ceiling.

[kojikun]

do a study and right up a report on the subject.