[Radiance-general] metal material - roughness

[Chris Coulter]

Thanks Greg -
I assumed it wouldn't be that straight forward but was curious.
We wanted to have Peter/pab-opto analyze the sample, but the client went a different direction.

Chris

From: Greg Ward [mailto:gregoryjward at gmail.com]
Sent: Monday, September 11, 2017 11:21 AM
To: Radiance general discussion <radiance-general at radiance-online.org>
Subject: Re: [Radiance-general] metal material - roughness

** External E-Mail **
Hi Chris,

The reason roughness is defined as the RMS surface "slope" is because you need to know the surface height deviation over the average correlation distance.  Both values would be measured in distance units, which cancel out to give you RMS roughness.  (This assumes a Gaussian surface profile.)  You may have measured the height deviation, but without an estimate of correlation distance, you can't get to roughness.  It's often best to adjust the roughness until it looks similar to the surface you are modeling, since these parameters are difficult to measure even with a good profilometer.

Cheers,
-Greg



From: Chris Coulter <Chris.Coulter at BuroHappold.com<mailto:Chris.Coulter at BuroHappold.com>>

Date: September 11, 2017 6:02:36 AM PDT


Hello Radiance gurus!

I have a quick question about defining roughness in a metal/plastic material. The reference manual describes roughness as �the rms slope of surface facets�.
We had a sample tested and the lab has given us this value back, something in the order of magnitude of a few hundred microns. Does this number get input as the roughness factor (after converting microns to meters)?

This number is quite small, but for a metal panel surface it could be correct. Just curious how to take the input and make it a bit more useful.
Thanks in advance. Sorry to have missed everyone in Portland, hopefully next time!

Chris

Chris Coulter
Associate
BuroHappold Engineering | Lighting Design
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