Why should they? Light rays keep going in a straight line until something happens to them.
Suppose the rays hit a perfectly black wall - they just get absorbed there (they become heat).
Suppose instead they hit a typical painted white wall. This will reflect some (not all) of the light and absorb the rest. It's a diffuse reflection, so the light scatters, but it doesn't scatter perfectly - you don't get the same intensity in all directions. In fact you get the most reflection at an equal angle to the incident light, just like a mirror, only not as sharply defined.
Now you have the reflected part of the original rays scattering through the entire room. Of course the rest of the room will be less bright than the spot the rays are hitting. The spot the rays are hitting is being illuminated directly - the rest of the room has to "make do" with what's reflected of the original rays, spread through the entire room.
Basically every time the rays reflect off of something the intensity is reduced due both to absorption and to spreading (diffusing).
because light propagates in straight lines and because the window is very large compared to light wave length so the light diffraction will be negligible
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Verified answer
Why should they? Light rays keep going in a straight line until something happens to them.
Suppose the rays hit a perfectly black wall - they just get absorbed there (they become heat).
Suppose instead they hit a typical painted white wall. This will reflect some (not all) of the light and absorb the rest. It's a diffuse reflection, so the light scatters, but it doesn't scatter perfectly - you don't get the same intensity in all directions. In fact you get the most reflection at an equal angle to the incident light, just like a mirror, only not as sharply defined.
Now you have the reflected part of the original rays scattering through the entire room. Of course the rest of the room will be less bright than the spot the rays are hitting. The spot the rays are hitting is being illuminated directly - the rest of the room has to "make do" with what's reflected of the original rays, spread through the entire room.
Basically every time the rays reflect off of something the intensity is reduced due both to absorption and to spreading (diffusing).
The light is straight beam of photons and it moves in straight lines. It can not bend or change direction unless it is reflected or refracted.
I hope that was useful
Best regards
because the waves are bouncing all over the place and some of it just gets reflected back out the window
because light propagates in straight lines and because the window is very large compared to light wave length so the light diffraction will be negligible
check this
http://en.wikipedia.org/wiki/Diffraction
I think its a thing called refraction.