Difference between a white body and a mirror

[n***@yahoo.com]

If a white body reflects all the incident light, and so does a mirror,
what essentially is the difference between the two? Why are mirrors
not white?

Also, how do we explain a transparent body? Is it simply a body that
allows light to pass through (as opposed to a black body, which absorbs
all the incident light or a white body, which reflects all the incident
light)?

Thanks,
Nimmi

[Sam Wormley]

Post by n***@yahoo.com
If a white body reflects all the incident light, and so does a mirror,
what essentially is the difference between the two? Why are mirrors
not white?

Check out the difference between "specular" and "diffuse".

Post by n***@yahoo.com
Also, how do we explain a transparent body? Is it simply a body that
allows light to pass through (as opposed to a black body, which absorbs
all the incident light or a white body, which reflects all the incident
light)?

That's a bit more complicated... and to make progress, quantum
mechanics is required.

[N:dlzc D:aol T:com (dlzc)]

Post by n***@yahoo.com
If a white body reflects all the incident light, and
so does a mirror, what essentially is the difference
between the two? Why are mirrors not white?

Sam's response is as simple and clear as this can be put.

Post by n***@yahoo.com
Also, how do we explain a transparent body? Is
it simply a body that allows light to pass through
(as opposed to a black body, which absorbs
all the incident light or a white body, which reflects
all the incident light)?

Yes. There are "transmission" or propagation effects in
transparent bodies, that one does not have in empty space.

And through all this you seem to be idealizing into perfect
surfaces. All real materials behave other than perfectly. For
example a typical aluminized glass mirror that is clear to
visible light, is black to both (far) IR and UV, and completely
transparent to radio (the geometry of a typical mirror just
"skips over" the mirror) and X- or gamma rays (which punch
straight through). Even in visible light, there is absorption by
the glass, and non-specular scattering in the glass and off of a
not-quite-perfect metalized surface. Don't worry too much about
this yet. Just keep in mind there are roots and rodent holes in
this field you are crossing...

David A. Smith

[Andy Resnick]

Post by n***@yahoo.com
If a white body reflects all the incident light, and so does a mirror,
what essentially is the difference between the two? Why are mirrors
not white?

It's the difference between specular and diffuse scattering. Diffuse
scattering typically occurs for rough surfaces. The most general
formulation for reflection is the "bidirectional reflectance
distribution function", and most surfaces have a BRDF consisting of a
specular lobe over a diffuse background.

See also "Lambertian surface"

Post by n***@yahoo.com
Also, how do we explain a transparent body? Is it simply a body that
allows light to pass through (as opposed to a black body, which absorbs
all the incident light or a white body, which reflects all the incident
light)?

Yep, that's pretty much it. One can call it "forward scattering" as well.