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A friend of mine unintentionally did an optics experiment. Basically, she wanted to cover her bedside lamp with a pattern of small holes, although she wanted the light projected from the bedside lamp to be homogeneous, i.e., like a normal bedside lamp. But when she did it, she realized the light from the bedside lamp's light bulb in fact projected a pattern of small holes! Then, she tested it with her smartphone flashlight, and this time the light was projected homogeneously!

So, how to explain it? I guess it much probably has to be with the size of the light bulb compared with the flashlight, but I can't see how exactly it explains that...

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I drawed two different sized lamps that illuminate a screen trough an obstacle with two holes. I hope I succeeded in making its self explanatory, if not: I have drawn the "limit photons" for each hole. By that I mean the two photons between which all the other photons are that went trough the same hole. You can see that for a larger (and large might also mean close) light source the areas illuminated by both holes is larger then for the small light source, where a shadowy area remains.

Two different sized lamps with obstacle and projection surface.

You can also see that the distance between the projection surface plays a role. If you'd put i really close to the obstacle you would have a shadow area even for the big light source. So distance/size of the light bulb and distance of the projection surface and of course the size and distribution of holes. I hope this helped.

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