OK Kelvin, if these aren't interference patterns, what are they? Republished 2/6/2018

Photo taken in February. First published for Feb 28, 2009

My brother is a physics professor, who teaches optics. He said years ago that I couldn't be seeing interference patterns on a macroscopic scale, from light coming through a narrow crack in a door hinge.

Here, the light is coming sideways through a narrow gap between a curtain and window frame. The bands certainly look like interference patterns to me. (When I was an oceanography student, I used to watch the waves reflecting off the sides of the ship canal as I walked to school. They made interference patterns as they crossed. I also knew all the types of wave patterns I could get in a coffee cup from my hand shaking as I walked across the cafeteria.)

This is a South-facing window, and the photo was taken on 2-28-2007. It has been photoshopped only to bring out the best in the image. I think that if the light is coming sideways to the opening, you can get the effect of a very narrow slit.

Or, if these aren't interference patterns, what are they?


The vertical lines are possibly from the vertical bars on the porch railings. Although the railings are less than waist-high; the early morning sun would have to be very low down to cast light through them up to this ceiling. I don't think the sun through the trees could be that low; maybe a reflection off a pan of water?This is early morning light, by the angle, and it comes through a lot of trees, so it is often a focused beam, coming through a narrow gap between the trees, as can be seen sometimes casting wavery light through the old float glass windows. (Pictures previously published.)