[Radiance-general] Luminaire modelling using Radiance

[Thomas Bleicher]

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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