[Radiance-general] Re: BRTDfunc for dichroic film? (was mixfunc for dichroic film?)

[John An]

You can download and view an information sheet describing the 
characteristics of a specifically engineered dichroic film at:
http://www.mmm.com/about3M/technologies/lightmgmt/pdf/dfa-50-88.pdf

Basically, the film is spectrally selective, and only transmits light 
at very specific wavelengths, and reflects all other wavelengths as if 
it were a mirror.  Depending on the incident angle of light in 
relationship to the surface, a different wavelength (within the band 
that the film transmits) is transmitted.  For instance, imagine a white 
piece of paper directly below a light source, and you were holding a 
dichroic film between the light and the paper.  As you incline and 
decline the film, the color transmitted through the film changes (in 
the specific example at the url above, from purple to blue to purple).  
Now imagine that you are looking through the film out a window, holding 
the film perpendicular to the direction of view.  As you rotate the 
film about either the z-axis or the y-axis, the scene shifts from 
purple to blue to purple, AND the greater the angle of rotation, the 
more reflective the material appears, until at a certain angle, the 
film behaves almost like a perfect mirror.

Thus, I was hoping that in Radiance (since it is a ray-tracing 
program), information regarding the direction and angle of the light, 
and direction and angle of view is probably already calculated.  If we 
could use this information to determine if-then switches, then a 
material such as dichroic films which exhibit different behavior under 
different conditions could be modeled.

I hope I've been clear.  Any insight into if this would be possible 
using BRTDfunc or mixfunc or any other func would truly be appreciated.


Thanks.


John

ps. Dichroic films are not yet a commonplace architectural material.  
However, the premise behind trying to model this material is to 
speculate and experiment with how such a material could be used 
(whether for aesthetic and/or energy purposes) in an architectural 
context without the expense and cost (time and money) of a full-scale 
mock-up.  Basically, behavior this material exhibits in a scaled 
physical model is not indicative of how it will behave in a real 
environment, and thus Radiance seems to be the perfect tool to explore 
this material.


> Jack de Valpine wrote:

> Message: 5
> Date: Sun, 29 Feb 2004 23:29:09 -0500
> From: Jack de Valpine <jedev at visarc.com>
> Subject: Re: [Radiance-general] mixfunc for dichroic film?
> To: Radiance general discussion <radiance-general at radiance-online.org>
> Message-ID: <4042BC15.2060506 at visarc.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hey John,
>
> My apologies, although I seem to remember somebody somewhere talking
> about dichoic glazing in radiance (albeit a long time ago), after 
> having
> followed my own advice to check in the archives, I have not been able 
> to
> find anything. In any event, I think that something like BRTDfunc or
> perhaps transfunc will do what you want. Do you have any performance
> data that you can share so people can get a better sense of the
> performance characteristics of the material.
>
> -Jack
>