Seeing what we see

1. Jun 27, 2011

nouveau_riche

i am new to physics so had a question regarding appearance of objects
firstly-why do we see the objects as they appear?
secondly-consider a situation wherein i am seeing the reflection of the bulbs above me on the reflecting surface on the ground,but i could not see those bulb refection from the side walls because they aren't reflective enough,also the only light producing element are those bulbs
the question that goes is
"why do i see side walls as walls but not as blurred reflection of bulbs?"

2. Jun 27, 2011

danR

Last question: Sometimes you do, if the walls are slick enough. But normally the walls are not completely flat at the microscopic level; they break up the direct rays from the bulb and throw them in little pieces in every direction.

3. Jun 27, 2011

chrisbaird

Objects either reflect light in straight lines (mirror), reflect light diffusely (wall), refract light (glass cup), or absorb light (black hair) and our brain has figured out how to construct an internal 3D image from the light (or lack of) that come from the object and enters our eyes. Why don't we typically see reflected images in walls? For the same reason you can look out a window and see a tree but if you look out a frosted window you don't. If the light gets jumbled up, you can't form images. Interestingly, most materials become highly reflective at grazing viewing angles. So if the wall's surface is not too rough, and you place the light bulb right near the wall and your head near the wall, you will be able to see a light bulb image reflected in the wall.

4. Jun 28, 2011

nouveau_riche

do we have any theory about how brain construct these images just out of light?

5. Jun 28, 2011

nouveau_riche

how does throwing light from a bulb into pieces due to roughness gives the perception of wall not of blurry bulb?

6. Jun 28, 2011

danR

Think of it this way: you have a sheet of perfectly smooth aluminum foil. It reflects the bulb perfectly; you may not even notice the foil if it's that perfect.

crumple the surface a bit. The light bulb image breaks up somewhat, but you can still make something of it out. Crumple it more and more. The bulb gradually disappears into thousands of tiny bits as its rays are thrown into to your eyes not only from the direct reflection, but from every part of the aluminum foil.

The technical names for these appearances are 'spectral' and 'diffuse', respectively, and CGI imaging exploit these properties, and graphic artists are familiar with the phenomena.

Now you're not really seeing the bulb at all, just a big surface of white. The wall-paint is a little different, there are also refraction effects from the titanium dioxide white or whatever pigment, but the principle is the same: you're getting bits of reflection/refraction/dispersion of the light bulb from all over the surface and now you are really 'seeing' the wall. That is precisely what 'wall-appearance' consists of. That is the 'image' of what we perceive and call, a 'wall'.

But if there is a bit of surface sheen or slickness in the paint surface, then you still have a bit of mirror-like residue and you still see also a bit of the bulb.