calculating CRI and CCT

Dear all,

Has anyone had the need and therefore figured out how to calculate CRI at a specific point within a daylit scene using Radiance? Specifically I'm thinking of John Mardaljevic's paper on electrochromic glass where he used a spectrometer to get CRI of different combinations of glass tint.

I was thinking of using different HDR sky capture photos within gendaylit to simulate different sky conditions, and therefore was wondering also if there is a way to calculate CCT and SPD of these sky images with and without sun.

I'm in the early stages of scratching my head around all this, and as such may be barking up the wrong tree.

Thanks.

Chris

···

On Feb 23, 2015, at 1:27 PM, Greg Ward <[email protected]> wrote:

Hi Reiner,

It's true that this behavior is not properly documented. If you can suggest a logical place where you would expect to find it, perhaps I can add the appropriate text.

Since rfluxmtx and rmtxop are new, the documentation is not as complete as it should be.

Cheers,
-Greg

From: Reinier Zeldenrust <[email protected]>
Subject: Re: [Radiance-general] Radiance-general Digest, Vol 132, Issue 12
Date: February 23, 2015 9:59:29 AM PST

Hi Mostapha,

Thank you - helpful! Where is this behaviour documented? I could not find it in the rfluxmtx or rcontrib manpages.

Best,

Reinier Zeldenrust
Environmental Designer
Atelier Ten
Environmental Design Consultants + Building Services Engineers

CIBSE Building Services Consultancy of the Year 2011
UK-GBC Sustainability Consultant of the Year 2009

Message: 1
Date: Fri, 20 Feb 2015 11:59:55 +0000
From: Reinier Zeldenrust <[email protected]>
To: "[email protected]"
   <[email protected]>
   
Content-Type: text/plain; charset="us-ascii"

Hi all,

I am following the latest approach to the three-phase method as described in Andy McNeil's 2014 Radiance Workshop Presentation, but when I generate view matrices my output is botched.
With this command (I realise this is low accuracy, but for the moment I'm mainly testing workflow) :
   rfluxmtx -ab 4 -ad 5000 < ChEast.pts - windows_pts/window_00.rad material.rad ChEast.rad > viewpts_00.mtx the header in the viewmatrix is as follows:
   #?RADIANCE
   oconv -f material.rad ChEast.rad windows_pts/window_01.rad
   rcontrib -fo+ -ab 4 -ad 5000 -faa -c 1 -f klems_full.cal -bn Nkbins -b kbin(0.525501,0.0136168,-0.850684,0,0,1) -m M-nor
   SOFTWARE= RADIANCE 4.3a lastmod by nrel_nt
   gugliel on rgugliel-W7-VM
   CAPDATE= 2015:02:19 12:21:14
   GMT= 2015:02:19 12:21:14
   NCOMP=3
   NCOLS=145
   FORMAT=ascii

When I try to do any matrix multiplication to get the three-phase result, I get problems with RMTXOP or dctimestep, which complain they can't load the matrix. If I add the line NROWS=81 (number of sensor points) manually in the header, I do get results. But I'm trying to run the simulation for a lot of windows so adding this line each time manually or with a script is a bit painful. Am I doing something wrong or is this a bug?

Additionally, when I try to run dctimestep in annual mode, using the following command:
   dctimestep -n 8760 viewpts_00.mtx grate.xml daylight_00.mtx annual.smx > test.dat I get:
   'fatal - unexpected EOF reading annual.smx'
even though my annual.smx has 146 rows (for all 146 Tregenza daylight patches) and 8760 columns.

Any idea what is going wrong here?

Many thanks,
Reinier

Reinier Zeldenrust
Environmental Designer
Atelier Ten
Environmental Design Consultants + Building Services Engineers

------------------------------

Message: 2
Date: Fri, 20 Feb 2015 09:48:26 -0500
From: Mostapha Sadeghipour <[email protected]>
To: Radiance general discussion <[email protected]>

Hi Reinier,

You need to use the -y option to specify the number of rows in your rfluxmtx run so you don't need to do it manually.

Cheers,
Mostapha

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Hi Chris,

I don't think there's an easy way to do this with Radiance. If you have complete spectral information for the sky, you can perform a multi-pass spectral calculation by substituting the appropriate components and material reflectances/transmittances for your subdivided spectrum. There are a few posts related to this in the list archives. Try searching on "spectral".

Cheers,
-Greg

···

From: Christian Humann <[email protected]>
Subject: Re: [Radiance-general] calculating CRI and CCT
Date: February 23, 2015 10:52:34 AM PST

Dear all,

Has anyone had the need and therefore figured out how to calculate CRI at a specific point within a daylit scene using Radiance? Specifically I'm thinking of John Mardaljevic's paper on electrochromic glass where he used a spectrometer to get CRI of different combinations of glass tint.

I was thinking of using different HDR sky capture photos within gendaylit to simulate different sky conditions, and therefore was wondering also if there is a way to calculate CCT and SPD of these sky images with and without sun.

I'm in the early stages of scratching my head around all this, and as such may be barking up the wrong tree.

Thanks.

Chris

Hi Chris,

The basic data and procedure for calculating CRI, CCT and others can be gleaned from this Matlab procedure:

http://www.lrc.rpi.edu/programs/nlpip/lightinganswers/lightsources/scripts/NLPIP_LightSourceColor_Script.m

Extrapolating from RGB to the required resolution is probably not for the squeamish. I was going to try out the above-linked code to compare (Matlab) computed CRI & CCT with what the MK350 was giving me, but never got round to it. For me, one of the 'take home' messages from tinkering with the MK350 (assuming the values are correct) was not to give too much importance to CRI or CCT alone -- much more informative to have the pair. Better still, of course, the spectrum.

The SAGE Glass White Paper is available here:

http://sageglass.com/wp-content/uploads/2011/08/How_to_maintain_neutral_daylight_illumination_wtih_SageGlass_EC_Glazing.pdf

A journal paper on same has been accepted for publication by LR&T.

Cheers
John

John Mardaljevic PhD FSLL
Professor of Building Daylight Modelling
School of Civil & Building Engineering
Loughborough University
Loughborough
Leicestershire
LE11 3TU, UK

Tel: +44 1509 222630 (Direct)
Tel: +44 1509 228529 (Pam Allen, secretary)

[email protected]<mailto:[email protected]>

http://www.lboro.ac.uk/departments/civil-building/staff/mardaljevicjohn

Personal daylighting website:
http://climate-based-daylighting.com

[cid:[email protected]]