[Radiance-general] Luminaire modelling using Radiance

Sat Aug 8 15:52:45 PDT 2015

"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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>>> Radiance-general mailing list
>>> Radiance-general at radiance-online.org
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>>>
>>
>>
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