# An interesting way to get an interference pattern

## Main Question or Discussion Point

OK so before I begin I will ask that you forgive me because I do not have a working knowledge of the mathematics involved here and I am admittedly not even at a novice level of understanding these things. However I have done at least some research and understand how an interference pattern does emerge when passing light through two slits.

I made a video that shows an interference pattern emerge in a totally different way and i need some help in understanding why. Please watch this video in the highest resolution possible, preferably in 1080p. Also please disregard what I am saying in the video because I would like to keep the focus on why this pattern emerges rather than the terrible science being done in it. I also encourage you to try this yourself so that you can see the pattern with your eye rather than in my video. Plus it is super easy. This does not work with all screens and not all screens produce the same pattern that you will see here. This does however work with any type of light you use (or that I have used). Thank you in advance and I hope you enjoy.

Last edited by a moderator:

## Answers and Replies

Related Other Physics Topics News on Phys.org
I think you made the right guess at the end of your video already : it's the pixels, the dense periodic succession of vertical lines in the structure of the screen. You can find more detailed explanations in the wikipedia article "Diffraction grating".

An interference from 2 slits, alternates fat zones of light with thin zones of dark. Well this description is just the effect of an optical illusion as the intensity curve is in fact a sinusoid, but the eye feels more contrast for the same luminosity variation when it takes place in the dark than in the light.

But the interference resulting from a periodic system, is thin peaks of light separated by relatively large margins of dark, which is what we observe on screens.

1 person
Thank you for the response and for watching my video. I read that article before posting this video and searched through images of diffraction grating and did not see much that resembled the same pattern as I was getting here. In most of the examples that you see it is light passing through a screen rather than light reflecting off of a screen.

I found it really interesting that you get the same effect whether the laptops screen is on or off and the light coming from the screen itself has no effect at all on the pattern you get other than making it slightly more difficult to see.

Borek
Mentor
You should be able to see similar difference pattern by reflecting the light from the laser diode from CD surface.