I have just been installing a couple of mosquito nets for windows in our apartment. The material is polyester, fibers are approximately 0.2mm thick, and the hexagonal "holes" apprixmately 1.5mm in diameter.

Just like the packaging says ("buy black ones if you want to have a better view"), the black ones are almost invisible from a little distance (~2 meters, its a little bit darker, almost in effect like an ND photo filter). From the same distance, the white ones are clearly visible, with good eyes you can also spot the "holes" (the effect looks almost like if you put the black point in photoshop into a much whiter area, making the contrast much less).

Why is that so? Is there a physical effect that objectively reduces the "image information" that reaches the human eye?

I would appreciate an answer that -- if applicable -- contains a short average human explanation, and additional one that goes a bit more in-depth into the "hobbyist physics" level

  • $\begingroup$ I'm guessing that a white grid will get blurred (circle of confusion and all that), but when a black grid gets blurred, the colours around it will prevail. $\endgroup$ – jinawee Jun 20 '14 at 8:50

This is similar to the reasons one way mirrors work.

If you look through a black net then no light is reflected from the net so the eye sees only the light coming from the objects on the far side of the net. The amount of the external light that reaches you is reduced, but the brain is pretty good at reconstructing images from only partial data, so the view looks unchanged.

If you look through a white net then the eye receives a mixture of the light reflected from the net and the light from outside transmitted through it. If the room you are in is dark and the outside is bright, then the amount of light reflected from the net is small compared to the transmitted light and you still don't see the net. However if the room is light and the outside dark then the light reflected from the net swamps the light transmitted and you only see the net. In between you'll see both the net and the view.


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