https://imgur.com/a/EJEp1P8
I understand that light acts as a wave and there is interference effects going on here but that’s about as far as my understanding goes. The situation confuses me even more considering there is only one light source.
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I don’t think this is due to anything like wave interference at all. Instead it is just a simple consequence of light diffusion.
Think about the light just as it comes passing through the holes in the grid. They don’t have perfectly sharp edges because it is scattered and diffused by the air. Even the shadowed areas have *some* amount of light falling on them as reflected from other areas of the room, otherwise they would be pitch black and you wouldn’t see anything at all in them.
The patches of light closest to the window are the smallest though so let us think of those as being 100% brightness. As we look farther away from the window the patches of light get larger and as a consequence dimmer at any given point; it is the same amount of light covering a larger area, so it is spread out and becomes less intense. Those patches of light are going to keep spreading out as they get more distant from the window and diffuse more, until the light patches are directly adjacent to each other. You can see this a little more than halfway through the pattern where it becomes an almost completely even patch of light with hardly any visible shadows.
As each patch of light keeps expanding eventually they start to overlap each other. The center of each patch then only has the light intensity left over from being scattered, say 35% of the intensity close to the window, but the patches of overlap combine the intensity from two adjacent holes and get up to 70% brightness! The brightest parts now are the areas between each patch of light, the areas which were previously in shadow.
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