[Radiance-general] Luminaire modelling using Radiance

Germán Molina Larrain germolinal at gmail.com
Wed Nov 11 12:56:40 PST 2015 

Hi Greg,

Thanks very much for the information. I tried what you said, and I think
that you might be slightly wrong.

- At First I did what you said... multiplied the original A1 value in
brightdata (127.324) by Pi and by R2 (0.05*0.05) and the returned number
was ridiculously close to 1, which is the -m option I input.

- I checked the surce.cal file, and the boxcorr requires A1, A2, A3 and
A4... the first one being a multiplier and the others being the length,
width and depth of the box. Using A1...A4 = 1 0.1 0.1 0.1, I got the
following results

TOP VIEW <https://drive.google.com/file/d/0B2NfkTSl19hQVkdzN1JlWFllcE0/view>
BOTTOM VIEW
<https://drive.google.com/file/d/0B2NfkTSl19hQVXRvTXRWYV9hR2s/view?usp=sharing>

One of them is using just ies2rad , the second is using ies2rad -i 0.05 and
the third one is transforming this to a box as explained before.... *THEY
LOOK GOOD TO ME...?*

I think the area and that kind of things has to be used for planar
surfaces. right? I mean, for when we do crazier boxes...?

Regards,

Germán

2015-11-11 16:40 GMT-03:00 Greg Ward <gregoryjward at gmail.com>:

> Hi Germán,
>
> Yes, it is a little more complicated, and you are right to worry about
> normals!  Actually, it is the projected area that matters, which for the
> sphere is (mostly) constant.  The main thing you need to do is to compute a
> first real brightdata argument (A1) equal to the existing one produced by
> ies2rad, multiplied by PI*R*R, where R is the radius of the original
> sphere.  Multiplying the value thus by the projected area of the emitter
> gets you back to radiant intensity.  Then, use the "boxcorr" function as
> the first string argument to the brightdata primitive in order that this
> radiant intensity is divided by the projected area in the appropriate
> direction during rendering.
>
> It would be prudent to verify the results by rendering illuminance in a
> large sphere around the light source before and after, just to make sure
> neither of us messed up!
>
> Cheers,
> -Greg
>
> *From: *Germán Molina Larrain <germolinal at gmail.com>
>
> *Subject: *Re: [Radiance-general] Luminaire modelling using Radiance
>
> *Date: *November 11, 2015 9:29:48 AM HST
>
>
> Hello again guys,
>
> I have a question now.... I have been reading about all this, and I would
> like to input geometry surrounded by illum. However, ies2rad seem to only
> be able to generate a Sphere. How do I try this with different shapes?
> (i.e. a box) is it just a matter of deleting the Sphere and put a lot of
> Polygons with the same modifier? I am worried about normals and stuff like
> that.
>
> I hope I made myself clear, haha
>
> Regards,
>
> Germán
>
> 2015-08-10 10:24 GMT-03:00 Germán Molina Larrain <germolinal at gmail.com>:
>
>> well, thanks a lot guys! I have a lot to read, write, try and see now....
>> I will let you guys know how this goes and come back with a lot of new
>> questions, haha.
>>
>> Best,
>>
>> Germán
>>
>> 2015-08-08 19:52 GMT-03:00 Randolph M. Fritz <rmfritz3 at gmail.com>:
>>
>>> "Further to Randolph’s post, the idea is to wrap the luminaire
>>> geometry as tightly as possible using the shapes Randolph mentioned,
>>> but this enveloping geometry will have *illum* applied to it, not
>>> glow"
>>>
>>> Duh. Rob is, of course, quite correct.
>>> --
>>> Randolph M. Fritz, Lighting Design and Simulation
>>> +1 206 390 4477 || rmfritz3 at gmail.com
>>>
>>>
>>> On Sat, Aug 8, 2015 at 1:59 PM, Rob Guglielmetti
>>> <rob.guglielmetti at gmail.com> wrote:
>>> > Thomas has great info on lamp color and using replmarks.  Further to
>>> > Randolph’s post, the idea is to wrap the luminaire geometry as tightly
>>> as
>>> > possible using the shapes Randolph mentioned, but this enveloping
>>> geometry
>>> > will have *illum* applied to it, not glow. The glow is used to
>>> illuminate
>>> > the luminaire geometry itself so that it appears realistic in a
>>> rendering.
>>> > You apply glows to the lamp objects in the luminaire generally, or you
>>> could
>>> > apply them to any shades or lenses in the luminaire.
>>> >
>>> > The luminous intensity of the illum is derived from the input lumens
>>> in the
>>> > IES file and is modulated by a few cal files, which use the candela
>>> values
>>> > from the IES file. The lamp color utility can give you reasonable
>>> values to
>>> > use for the glows, based on lamp input lumens. Again, the glows
>>> illuminate
>>> > the local luminaire geometry, and the illums actually illuminate the
>>> space.
>>> > The ileum material is invisible when viewed directly, which is why you
>>> need
>>> > the glows to make the luminaries appear correct in a rendering. The
>>> flux
>>> > from the glow also does not make it past the illum geometry and so it
>>> does
>>> > not contribute to the scene illumination or any calculations.
>>> >
>>> > There is some info on using illums and glows here:
>>> >
>>> >
>>> http://www.rumblestrip.org/using-the-illum-material-for-smoother-renderings-in-radiance/
>>> >
>>> > I did a bunch of crap with different illum geometry and cal files
>>> > (lboxcorr.cal et al.) and got pretty good at picking the best ones for
>>> the
>>> > jobs at hand (wall mounted sconces and stuff like that can be tricky
>>> to get
>>> > looking “right”), but never got around to posting a summary on that
>>> stuff. A
>>> > good place to start is just running a few different luminaire types
>>> though
>>> > ies2rad and see what you get, and then play with the output files from
>>> > there.
>>> >
>>> > Are we having fun yet?
>>> >
>>> > -Rob
>>> >
>>> > From: Randolph M. Fritz <rmfritz3 at gmail.com>
>>> > Reply: Radiance general discussion <
>>> radiance-general at radiance-online.org>>
>>> > Date: August 8, 2015 at 2:32:01 PM
>>> > To: Radiance general discussion <radiance-general at radiance-online.org
>>> >>
>>> > Subject:  Re: [Radiance-general] Luminaire modelling using Radiance
>>> >
>>> > The basic technique is to wrap the visible geometry of the luminaire,
>>> if
>>> > any, with a glow in a simple shape that actually radiates the light.
>>> The
>>> > glow is transparent, so that the geometry can be seen, and direct
>>> > illumination does not pass through the glow, so light can be used
>>> internal
>>> > to the glow to give the luminaire a realistic look.
>>> >
>>> > The glow geometry and description may be generated by ies2rad. IIRC
>>> only
>>> > four shapes are supported: sphere, rectangular, cuboid (box), and thin
>>> disc.
>>> >
>>> > Ies2rad does not support eulumdat and again, IIRC, has not been
>>> updated to
>>> > support the latest IES photometry standard, LM-63-02.
>>> >
>>> > --
>>> > Randolph M. Fritz, Lighting Design and Simulation
>>> > +1 206 390 4477 || rmfritz3 at gmail.com
>>> >
>>> > On Sat, Aug 8, 2015 at 7:46 AM, Thomas Bleicher <tbleicher at gmail.com>
>>> wrote:
>>> >> Hi German.
>>> >>
>>> >> The most important information you need you will find in the ies2rad
>>> man
>>> >> page. In general you use it to create a library of luminaire *.rad and
>>> >> *.dat
>>> >> files which you can later reference into your scenes via xform. I
>>> found it
>>> >> more convenient and flexible for my exporters to create files with
>>> >> triangular markers and use "!replmarks ..." to place multiple
>>> luminaire
>>> >> files. That way you can later replace all luminaires in an array with
>>> a
>>> >> single change in the scene file.
>>> >>
>>> >> When you write a plugin you have to pay attention to the units of the
>>> ies
>>> >> file and adjust the -d parameter accordingly. Unfortunately ies2rad
>>> >> doesn't
>>> >> read that information from the file.
>>> >>
>>> >> The geometry in IES files is limited to discs, ovals, rectangles and
>>> >> extrusions of these shapes. Mostly you will find the 2 dimensional
>>> shapes
>>> >> for recessed and spot lights while the 3 dimensional shapes are used
>>> for
>>> >> pendants (boxes and cylinders). If you want to avoid these crude
>>> things in
>>> >> your model and use detailed geometry instead (from a dxf file, for
>>> >> example)
>>> >> then you use the -i option to create an illum sphere. The sphere will
>>> be
>>> >> used with the luminance data generated from the ies file. You have to
>>> >> place
>>> >> the detailed geometry of fixture into the sphere yourself. ies2rad
>>> doesn't
>>> >> do that for you.
>>> >>
>>> >> I found that geometry provided by manufacturers is very detailed and
>>> can
>>> >> lead to problems in large models. MGF geometry information is
>>> extremely
>>> >> rare.
>>> >>
>>> >> You can use the -t option to set the lamp type. This defines the color
>>> >> temperature. The -m option allows you to set a maintenance factor
>>> that all
>>> >> artificial lighting calculations require. Not that some lamp type
>>> entries
>>> >> in
>>> >> the lamp.tab file already include a correction factor for the lamp so
>>> you
>>> >> have to take this into account when calculating the final value of
>>> -m. I
>>> >> found it safest to use "-t WHITE" (which does not have a correction)
>>> and
>>> >> lump all the efficiency reductions and maintenance factors together
>>> into a
>>> >> single -m value.
>>> >>
>>> >> European manufacturers provide are more likely to provide Eulumdat
>>> file
>>> >> specs for their luminairs. Sometimes they convert these for you into
>>> IES
>>> >> files. If you can only get LDT files you can use DIALUX or something
>>> >> similar
>>> >> to convert the LDT to IES files. It used to offer this option a few
>>> year
>>> >> ago, at least. There may be other converters out there, but I don't
>>> >> remember
>>> >> the names.
>>> >>
>>> >> Hth, Thomas
>>> >>
>>> >> On Fri, Aug 7, 2015 at 2:09 PM, Germán Molina Larrain
>>> >> <germolinal at gmail.com>
>>> >> wrote:
>>> >>>
>>> >>> Hello everyone,
>>> >>>
>>> >>> I think this might be a silly question, but I actually have not
>>> found too
>>> >>> much information on how to model luminaires using Radiance... I am
>>> asking
>>> >>> this because I want to add this feature to the plugin I am
>>> developing.
>>> >>>
>>> >>> What is the recommended method for modelling luminaires in Radiance?
>>> I
>>> >>> intend to use IES files as input. Hopefully I would also have the
>>> >>> geometry,
>>> >>> but I have to consider cases when this is not available.
>>> >>>
>>> >>> I know there is an IES2RAD program, but I am not quite sure how
>>> general
>>> >>> it
>>> >>> is. Also, I have heard about the use of illums (a sphere, for
>>> example)
>>> >>> that
>>> >>> covers the entire luminaire....?
>>> >>>
>>> >>> I am kind of lost, so if someone could give me a hint, I would really
>>> >>> appreciate it.
>>> >>>
>>> >>> Also, if someone know where to find information about IES files and
>>> their
>>> >>> format, that would also be really helpful.
>>> >>>
>>> >>> THANKS
>>> >>>
>>> >>> Germán
>>> >>>
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>>> >>>
>>> >>
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