[Radiance-general] Specular Reflections from Plastic?

[Greg Ward]

Hi Kristopher,

The reason ordinary materials do not create virtual light sources the
way mirror and the prism types do is because it would be too
expensive.  If you had two such surfaces facing each other with
a light source between them, they would potentially create an
infinite number of virtual light sources.  (This is why the -dr
option is there, to prevent such a calamity when using facing
"mirror" surfaces.)

If you want to have the material properties of plastic or metal,
with the virtual light sources of mirror, then use your plastic
or metal as the alternate type in your mirror specification.

What is the problem?  Is it simply not what you expected?
Did you expect it to create an infinite set of virtual sources
for you?  Then you should also expect the simulation to 
take forever.

-Greg

On Tue, 18 Jan 2005 09:56:11 -0600, Baker, Kristopher <kbaker at syska.com> wrote:
> Hello,
> 
> I have a fundamental question about Radiance that I can't figure out.
> What is the best way to get Source specular reflections from a plastic,
> metal, or trans material?
> 
> In my model, setting the specular component of the material at or near
> 1.0 correctly provides view reflections in the material (reflections of
> the window on the other end of the room).  However, there are no
> reflected solar patches, as is expected with direct sun landing on the
> reflective material.
> 
> Using the material type mirror, the virtual light source is created and
> the solar patch shows up, but when a plastic, metal, or trans material
> is specified with a specularity at or near 1.0, there isn't even a
> glimpse of the expected reflected solar patch.
> 
> As an example, imagine a window with a partition perpendicular to that
> window.  The sun is out and shining through the window onto that
> partition.
> 
> -If I make that partition a mirror material type, I see this wonderful
> reflected solar patch on the floor.
> 
> -If I make that partition a plastic, trans, or metal with a specular
> component of 1.0, there is no reflected solar patch on the floor.
> 
> >From my understanding, the mirror treats the reflected solar patch as a
> virtual light source and all is good, but it does not do this for
> plastic, metal, trans.
> 
> When the plastic, metal, or trans is set as specular, Radiance
> accurately shows the reflection of the view in the partition (in this
> case the window), but the direct solar flux that entered and hit the
> partition is gone, or at least transferred to the indirect or ambient
> component.
> 
> All parameters are defaulted at the medium level and I have bumped
> direct relays to 3 (lr=6, lw=.002, dr=3, st=0.1)
> 
> This is simple and a most fundamental calculation, but alas no dice.
> 
> Any ideas?  Thanks.
> 
> KB
> Kristopher S. Baker