Horizontals in a grid do not cast shadow while verticals do. Why is this? A friend shared this image and asked about the shadow. As it appears the horizontals are not casting a shadow while the verticals are. It seems that the light source is on the left hand side wall, based on the vertical shadows. So how can this be?
(https://i.stack.imgur.com/pHYB7.jpg)
Edit 1 - Not very clear but an image with the source of the light.
https://imgur.com/pmK2CxW
Edit 2 - A gif from a short video of the table under the light.
https://giphy.com/gifs/2uInVzY9vOBwbmh4Nw
Edit 3 - Another friend suggested that it might have something to do with the principles behind Young's double slit experiment (an answer says its not, I agree)
Edit 4 - https://giphy.com/gifs/jVEUnP6fiah53zdMcp
A video made in to a gif with the grid being moved around and the source of light shown in relation to the object
 A: If the light source is like a long fluorescent light, shadows in one direction (along the length of the fluorescent tube) will be blurred and shadows in the other direction will be fairly sharp.  Can you ask your friend to send you a photo of the light source (not of light reflected off the wall)?
A: The light should be one of those standard long white neon tubes. In the animated gif you can also see the very light shadows in the other direction. The wooden bars parallel to the lamp cover the light in its full length, while those orthogonal to the light tube cover only a small width. That's why the first are much more visible.
If you turn the table by 45° the shadows should form a rather even grid.
It doesn't really have much to do with a double slit experiment, which is used to prove a wave character. This appearance can also be explained purely with the particle character of the light, as light from the lamp can reach every part of the low shadow area in a straight line.
For the double slit experiment the slits have to be sufficiently narrow and on the screen behind it you will find maxima in places where there is no straight path to the light source.
A: Shadows perpendicular to the fluorescent tube light source are not visible as they appear to be producing multiple shadows from multiple light sources thereby cancelling their own shadows.
Shadows parallel to the fluorescent tube light source have a point light source on them and this causes sharp shadows to fall on the surface below.When the grid is tilted and lines no longer remain perpendicular,new shadows are formed as is visible in edit 4.
Sharing an image drawn by a friend of a friend who asked this question. I believe the question has been answered.
(https://i.stack.imgur.com/IYgPY.jpg)
