Lamp colour

Hi Folks,

I would be grateful if anyone would provide some insight to a problem I've
been trying to resolve for some time:

I am using fluorescent lamps in an office scene, and would like to model
colour temperatures of approx. 2200K and 6000K giving a warm white and
daylight white respectively.

I have read through the Radiance manual but am a little confused still as to
how to set lamp format file (.fmt) to give me the required colours.

I have generated a .dat file from the ies data for the lamp within which I
set the colour to the default set at 0.907 0.863 0.4762: I believe that this
represents 48 46 25% RGB values.

However, when I run a lighting illuminance simulation the .lum file refers
only to the lamp .dat file and .fmt file (not the .rad file generated by
ies2rad). Now upond exploring the .fmt file it refers to the 'void lamp
glow' in this instance its: 4 0 3.57 14.72 860

I think that this may be the line I need to change to alter the colour?
Unless it's already taken care of in the ies2rad conversion via the .dat
file in which case I need to alter the 0.907 0.863 0.4762 values relative to
desired K values. I'd be indebted to anyone that can provide the relevan
combination for the two lamp colours I'm looking for.

With kind regards,

Anthony Farrell
Dublin Institute of Technology

···

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Subject: Radiance-general Digest, Vol 15, Issue 11

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Today's Topics:

   1. Redirecting+scattering (Federico Giovannetti)
   2. Re: Redirecting+scattering (Greg Ward)
   3. Re: Redirecting+scattering (Jan Wienold)
   4. RE: Redirecting+scattering (Giulio Antonutto)

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

Message: 1
Date: Thu, 19 May 2005 15:24:09 +0200
From: "Federico Giovannetti" <[email protected]>
Subject: [Radiance-general] Redirecting+scattering
To: <[email protected]>
Message-ID: <002801c55c76$0a260f90$e400a8c0@PC501fg>
Content-Type: text/plain; charset="iso-8859-1"

Hallo Greg Ward, hallo Radiance Community!

I've been learning Radiance for a couple of weeks and i have to work
intensively with it in the next weeks, as I4m investigating the energy
saving potential and visual comfort of systems combining angular selective
and diffusing panes.

Now I have to simulate a simple test-room with a complex fenestration, which
includes an exterior prismatic structure as shading device and a diffusing
pane for glare control. I try to find out the best way to model the system
so as to get quantitative accurate results (RwR Chapters 10-13 and mails
archive) but i4m still a little bit confused....

- As to the prismatic structure, i will use the PRISM2 material as virtual
source. No redirection of diffuse incoming light and no dispersion are the
only limitations of this material. And it would make no sense to use the
PhotoMap port, because these materials are not implemented in this tool. Is
it right?

- As to the diffuser, i would intuitively treat it as an ILLUM with a BRTDF
function as alternate material (I4m measuring, modelling and comparing
different kind of diffusers) and run MKILLUM. If i understood correctly,
the BRTDF materials are only considered in the direct calculation and
indirect specular, but not in the indirect diffuse, where they are
approssimate to lambertian diffusers. Should i try another material?

- How are PRISM materials computed in the MKILLUM calculation of the window
light output? Should I better try to run the simulation without MKILLUM and
high ambient parameters (-ab, -ad, -as)?

- What if i measure the BRTDF of the complete system and i model it as a
normal light source? It is really difficult (or impossible) to get sharp
peaks in light output with high subsampling and jittering of the source?

Any other suggestion to simulate this system correctly (quantitative)?

Sorry for so many questions and THANKS A LOT for any contribution.

Regards,
Federico Giovannetti

---------------------------------------------------------
Federico Giovannetti
Institut f|r Solarenergieforschung GmbH
Am Ohrberg 1
D-31860 Emmerthal

tel: +49(0)5151-999-501
fax: +49(0)5151-999-500
e-mail: [email protected]
internet: www.isfh.de
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Message: 2
Date: Thu, 19 May 2005 08:08:13 -0700
From: Greg Ward <[email protected]>
Subject: Re: [Radiance-general] Redirecting+scattering
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; delsp=yes; format=flowed

Hi Federico,

It sounds to me like you are "diving into the deep end" as they say about
new swimmers who are very ambitious.

- As to the prismatic structure, i will use the PRISM2 material as
virtual source. No redirection of diffuse incoming light and no
dispersion are the only limitations of this material. And it would
make no sense to use the PhotoMap port, because these materials are
not implemented in this tool. Is it right?

I don't know about support in the photon map add-on, but the prism material
types do redirect diffuse rays as well. They just don't have a diffuse
component.

- As to the diffuser, i would intuitively treat it as an ILLUM with a
BRTDF function as alternate material (I4m measuring,
modelling and comparing different kind of diffusers) and run
MKILLUM. If i understood correctly, the BRTDF materials are only
considered in the direct calculation and indirect specular, but not in
the indirect diffuse, where they are approssimate to lambertian
diffusers. Should i try another material?

Your information is correct as far as I understand what you are saying. If
you can fit your measurements to a Gaussian lobe distribution, you are
better off using one of the native models
(trans or trans2), as all ray paths will be followed appropriately.
The general BRDF types, transfunc, transdata, and BRTDfunc, only use the
directional-diffuse lobe specified for interactions with light sources.
General ray sampling from an arbitrary distribution is quite expensive, and
not done in Radiance for that reason.

- How are PRISM materials computed in the MKILLUM calculation of the
window light output? Should I better try to run the simulation without
MKILLUM and high ambient parameters (-ab, -ad, -as)?

The diffuse portion of the window distribution through a prismatic glazing
will be computed by mkillum, leaving the "specular" (directional) portion to
be done during the final rendering. This is the correct behavior, and you
don't have to treat it specially with mkillum, which is helpful for
considering contributions from the sky, ground, and neighboring structures.

- What if i measure the BRTDF of the complete system and i model it
as a normal light source? It is really difficult (or impossible) to
get sharp peaks in light output with high subsampling and jittering
of the source?

I'm not sure what you mean, here. If you have some way to simulate your
exterior and measure the actual output distribution of the window system as
a light source, then you wish to represent that as a brightdata modifier on
a window polygon, this would work. It's a very challenging measurement
problem, though, which is why no one has done it to my knowledge. (Anyone
out there have information on this?)

The purpose of mkillum of course is to create a light source from your
surface(s) by simulating an outdoor situation. It doesn't always work,
though. Specifically, mkillum has trouble resolving the contribution from
the sun through curved, specular reflectors and devices. It can handle most
everything else.

Any other suggestion to simulate this system correctly
(quantitative)?

Measure and validate. Repeat.

-Greg

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

Message: 3
Date: Thu, 19 May 2005 16:07:40 +0200
From: Jan Wienold <[email protected]>
Subject: Re: [Radiance-general] Redirecting+scattering
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"

Hi Federico,

your task cries for using photon-mapping...

You should model your shading system geometrically and use dielectric as
material (be careful about the surface orientation!). The diffusing material
can be modeled by trans material. If you have a complex scattering material,
you can adapt the trans material by an cal function. (Don't use BRTF-func or
data with the current photon-mapping version).

To be more efficient using the diffuse sky, you should define a photon-port,
where all the photons are emitted to. Usually the photon-port material is
the window pane.

Then you can simply run the simulations, direct and diffuse contributions
should be calculated correctly.

Last but not least, there exist also a version of daysim containing
photon-mapping, so you can run these simulations also hourly (or other
timesteps) if you want. Unfortunately, the latest daysim version didn't
compile with the photon-mapping extension - but if you need it, you can use
also the older version, Christoph could provide it.

Good luck!

Jan

Federico Giovannetti wrote:

Hallo Greg Ward, hallo Radiance Community!

I've been learning Radiance for a couple of weeks and i have to work
intensively with it in the next weeks, as I4m investigating the energy
saving potential and visual comfort of systems combining angular
selective and diffusing panes.

Now I have to simulate a simple test-room with a complex fenestration,
which includes an exterior prismatic structure as shading device and a
diffusing pane for glare control. I try to find out the best way to
model the system so as to get quantitative accurate results (RwR
Chapters 10-13 and mails archive) but i4m still a little bit confused....

- As to the prismatic structure, i will use the PRISM2 material as
virtual source. No redirection of diffuse incoming light and no
dispersion are the only limitations of this material. And it would
make no sense to use the PhotoMap port, because these materials are
not implemented in this tool. Is it right?

- As to the diffuser, i would intuitively treat it as an ILLUM with a
BRTDF function as alternate material (I4m measuring, modelling and
comparing different kind of diffusers) and run MKILLUM. If i
understood correctly, the BRTDF materials are only considered in the
direct calculation and indirect specular, but not in the indirect
diffuse, where they are approssimate to lambertian diffusers. Should i
try another material?

- How are PRISM materials computed in the MKILLUM calculation of the
window light output? Should I better try to run the simulation without
MKILLUM and high ambient parameters (-ab, -ad, -as)?

- What if i measure the BRTDF of the complete system and i model it as
a normal light source? It is really difficult (or impossible) to get
sharp peaks in light output with high subsampling and jittering of
the source?

Any other suggestion to simulate this system correctly (quantitative)?

Sorry for so many questions and THANKS A LOT for any contribution.

Regards,
Federico Giovannetti

---------------------------------------------------------
Federico Giovannetti
Institut f|r Solarenergieforschung GmbH Am Ohrberg 1 D-31860 Emmerthal

tel: +49(0)5151-999-501
fax: +49(0)5151-999-500
e-mail: [email protected] <mailto:[email protected]>
internet: www.isfh.de <http://www.isfh.de>

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http://www.radiance-online.org/mailman/listinfo/radiance-general

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Message: 4
Date: Thu, 19 May 2005 16:31:09 +0100
From: "Giulio Antonutto" <[email protected]>
Subject: RE: [Radiance-general] Redirecting+scattering
To: "Radiance general discussion"
  <[email protected]>
Message-ID:
  <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"

you may also consider to have a look to radzilla

:wink:

This is a not official, not bullet proof, version of radiance that
incorporates all new additions + some really crazy Carsten
optimisations/changes/addons...

It seems really consistent and stable and I already modelled some prisms
with pmap within it (like a 500 modular prisms wall).

It works well!

I believe it's worthy to try and I have been really impressed by the latest
development.

The advantage over traditional radiance for me is that photon mapping is
performed through the rpict command without having to use mkpmap... but they
might be some bugs here of there.... watch out!

ciao,

giulio

________________________________

From: [email protected]
[mailto:[email protected]] On Behalf Of Federico
Giovannetti
Sent: 19 May 2005 14:24
To: [email protected]
Subject: [Radiance-general] Redirecting+scattering

Hallo Greg Ward, hallo Radiance Community!

I've been learning Radiance for a couple of weeks and i have to work
intensively with it in the next weeks, as I4m investigating the energy
saving potential and visual comfort of systems combining angular selective
and diffusing panes.

Now I have to simulate a simple test-room with a complex fenestration, which
includes an exterior prismatic structure as shading device and a diffusing
pane for glare control. I try to find out the best way to model the system
so as to get quantitative accurate results (RwR Chapters 10-13 and mails
archive) but i4m still a little bit confused....

- As to the prismatic structure, i will use the PRISM2 material as virtual
source. No redirection of diffuse incoming light and no dispersion are the
only limitations of this material. And it would make no sense to use the
PhotoMap port, because these materials are not implemented in this tool. Is
it right?

- As to the diffuser, i would intuitively treat it as an ILLUM with a BRTDF
function as alternate material (I4m measuring, modelling and comparing
different kind of diffusers) and run MKILLUM. If i understood correctly,
the BRTDF materials are only considered in the direct calculation and
indirect specular, but not in the indirect diffuse, where they are
approssimate to lambertian diffusers. Should i try another material?

- How are PRISM materials computed in the MKILLUM calculation of the window
light output? Should I better try to run the simulation without MKILLUM and
high ambient parameters (-ab, -ad, -as)?

- What if i measure the BRTDF of the complete system and i model it as a
normal light source? It is really difficult (or impossible) to get sharp
peaks in light output with high subsampling and jittering of the source?

Any other suggestion to simulate this system correctly (quantitative)?

Sorry for so many questions and THANKS A LOT for any contribution.

Regards,

Federico Giovannetti

---------------------------------------------------------
Federico Giovannetti
Institut f|r Solarenergieforschung GmbH
Am Ohrberg 1
D-31860 Emmerthal

tel: +49(0)5151-999-501
fax: +49(0)5151-999-500
e-mail: [email protected]
internet: www.isfh.de

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Hello Anthony,

Your question is a bit confusing. I don't know what lamp .fmt file you're talking about, and the numbers you give don't seem to make sense. The CIE (x,y) chromaticity coordinates corresponding to 2200K and 6000K sources are:

CT (K) CIE x CIE y
-------- -------- -------
2200 0.5056 0.4152
6000 0.3221 0.3318

Converting these to Radiance RGB values with Y=1.0, we get:

CT R G B
----- -- -- --
2200 1.881 0.7420 0.0636
6000 0.9078 1.032 1.049

If you use the "-t default" option and give these to the "-c" option of ies2rad, it will produce sources with the corresponding color temperature. However, I don't really believe this is what you want.

Applying a color to your light sources will yield a color cast in your rendered images, which is almost never desirable. Your eye tends to ignore such color casts in an environment -- this is called "color constancy" or "white balance" in photography.

If your true purpose is to determine how the color of your light source affects the visible colors of the objects in your scene, you need to start from the actual spectral power distribution of your illuminant (not just the color temperatures) and the spectral reflectances of your objects. The former may be obtained from the manufacturer in some cases. The latter must be obtained by measurements with a suitable spectroreflectometer. Then, rather than dealing with CIE (x,y) chromaticities, you need to apply a technique like the one described in the following paper:

     http://www.anyhere.com/gward/egwr02/

This paper describes the simplest and most economical approach if you want to know what your colors will look like under different illuminants. Any shortcut shorter than this will simply not work.

-Greg

P.S. In future, please be careful not to include an entire mailing list digest in your posting. It's an easy mistake to make with modern mailers -- they are ever so helpful and eager to please.

···

From: "Anthony J. Farrell" <[email protected]>
Date: May 23, 2005 1:51:10 PM PDT

Hi Folks,

I would be grateful if anyone would provide some insight to a problem I've
been trying to resolve for some time:

I am using fluorescent lamps in an office scene, and would like to model
colour temperatures of approx. 2200K and 6000K giving a warm white and
daylight white respectively.

I have read through the Radiance manual but am a little confused still as to
how to set lamp format file (.fmt) to give me the required colours.

I have generated a .dat file from the ies data for the lamp within which I
set the colour to the default set at 0.907 0.863 0.4762: I believe that this
represents 48 46 25% RGB values.

However, when I run a lighting illuminance simulation the .lum file refers
only to the lamp .dat file and .fmt file (not the .rad file generated by
ies2rad). Now upond exploring the .fmt file it refers to the 'void lamp
glow' in this instance its: 4 0 3.57 14.72 860

I think that this may be the line I need to change to alter the colour?
Unless it's already taken care of in the ies2rad conversion via the .dat
file in which case I need to alter the 0.907 0.863 0.4762 values relative to
desired K values. I'd be indebted to anyone that can provide the relevan
combination for the two lamp colours I'm looking for.

With kind regards,

Anthony Farrell
Dublin Institute of Technology

Greg,

Thanks for the very helpful advice. Unfortunately I cannot access the link
you gave me as it says 'object not found', what's the name of the paper?

Apologies if my email was confusing, to simplify, I wish to illustrate to an
audience the dynamics of artificial light in providing a warm and cool
environment relative to mixing light from 2000 to 6000K as is presented by
Philips
(http://www.lighting.philips.com/gl_en/index.php?main=global&parent=global&i
d=global&lang=en under' a new concept in office lighting ' and then to
compare that with actual warm (morning or evening) and cool (midday) light
from a window.

The lamp colour defaults are 0.907 0.863 0.4762

I wish to model the same lamp but with a colour of 2200 and 6000K resp.

I now understand that the ies2rad program translates the colour from the -t
and -c options into the .dat file which is used in generating the
distributions. The .fmt file must be one just used by DRAD, so not to worry
bout that.

Now when I consider the human eye things get complicated. There is no
spectral power distribution of the fluorescent illuminant and the spectral
reflectances of your objects are also not available. It is a very simple
office scene with angled desks, yellow chair, and light coloured partition
dividers. Can you suggest where I can get generic data of this kind? Or can
you suggest the best way to approach what I am trying to simulate?

Thanks,

Anthony

P.S. Apologies for attaching the mailing list, hope this one gets through in
proper format.

···

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Hi Anthony,

I believe that this is the paper that Greg is referring to:

http://www.anyhere.com/gward/papers/egwr02/index.html

-Jack

Anthony J. Farrell wrote:

···

Greg,

Thanks for the very helpful advice. Unfortunately I cannot access the link
you gave me as it says 'object not found', what's the name of the paper?

Apologies if my email was confusing, to simplify, I wish to illustrate to an
audience the dynamics of artificial light in providing a warm and cool
environment relative to mixing light from 2000 to 6000K as is presented by
Philips
(http://www.lighting.philips.com/gl_en/index.php?main=global&parent=global&i
d=global&lang=en under' a new concept in office lighting ' and then to
compare that with actual warm (morning or evening) and cool (midday) light
from a window.

The lamp colour defaults are 0.907 0.863 0.4762

I wish to model the same lamp but with a colour of 2200 and 6000K resp.

I now understand that the ies2rad program translates the colour from the -t
and -c options into the .dat file which is used in generating the
distributions. The .fmt file must be one just used by DRAD, so not to worry
bout that.

Now when I consider the human eye things get complicated. There is no
spectral power distribution of the fluorescent illuminant and the spectral
reflectances of your objects are also not available. It is a very simple
office scene with angled desks, yellow chair, and light coloured partition
dividers. Can you suggest where I can get generic data of this kind? Or can
you suggest the best way to approach what I am trying to simulate?

Thanks,

Anthony

P.S. Apologies for attaching the mailing list, hope this one gets through in
proper format.

--
# John E. de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction

Hi Anthony,

From: "Anthony J. Farrell" <[email protected]>
Date: May 24, 2005 9:19:34 AM PDT

Thanks for the very helpful advice. Unfortunately I cannot access the link
you gave me as it says 'object not found', what's the name of the paper?

Sorry about that -- I miscopied the link somehow. Jack got the right one in his response.

Apologies if my email was confusing, to simplify, I wish to illustrate to an
audience the dynamics of artificial light in providing a warm and cool
environment relative to mixing light from 2000 to 6000K as is presented by
Philips
(http://www.lighting.philips.com/gl_en/index.php?main=global&parent=global&i
d=global&lang=en under' a new concept in office lighting ' and then to
compare that with actual warm (morning or evening) and cool (midday) light
from a window.

Oh dear. Mixing illuminants is even more complicated, and not something Radiance does very well. For this to be done correctly, you really need a full-blown spectral lighting simulation. The problem is, there aren't any. You can trick Radiance into doing it by running multiple scenes and choosing different spectral sample wavelengths for RGB each time then combining the results, but it's a hassle and difficult to do right.

The lamp colour defaults are 0.907 0.863 0.4762

Is this RGB or Yxy (or ???)

I now understand that the ies2rad program translates the colour from the -t
and -c options into the .dat file which is used in generating the
distributions. The .fmt file must be one just used by DRAD, so not to worry
bout that.

Once again, what you'll get out of this technique is a simple color cast in your renderings, which will have almost nothing to do with how people might perceive the actual space, and doesn't tell you a thing either about how colors are rendered.

Now when I consider the human eye things get complicated. There is no
spectral power distribution of the fluorescent illuminant and the spectral
reflectances of your objects are also not available. It is a very simple
office scene with angled desks, yellow chair, and light coloured partition
dividers. Can you suggest where I can get generic data of this kind? Or can
you suggest the best way to approach what I am trying to simulate?

If you don't have spectral data, then this is an exercise in futility. You can't learn anything by modifying the source colors independent of the surfaces. Your results won't have any value or meaning.

-Greg