[Radiance-general] Re: direct/indirect photometric

[Greg Ward]

I don't really have time for this, so my answers are going to be short.

> From: John An <whollycow@mac.com>
>
> Chas and Greg,
>
> Thanks for the info.  I was away on a short vacation, and just got 
> back.  I'm still more than a bit confused about accurately modeling 
> direct/indirect luminaires.  Could you tell me if I have this right?
>
> Background info:
> My space is modeled in inches.
>
> The photometric file is in feet (as reported by ies_read):
>
> Luminaire Dimensions
> --------------------
> Measurement units =       Feet
> Width =                   0.46
> Length =                  4.00
> Height =                  0.00
>
>
> Question 1:  I have noticed that the height for all of the 
> direct/indirect luminaires is 0.  How is that physically possible?  
> More importantly, how would a dimension of 0 ever "enclose" the 
> geometry of the luminaire?

The heights are set to zero by ies2rad to avoid a "dark band" at the 
level of the luminaire when it's hung from the ceiling.  It's a hack to 
avoid artifacts.  You're right that it cannot enclose any geometry this 
way.

>
> Question 2:  The actual luminaire dimensions are larger than the 
> dimensions given by ies_read.  For instance, the length of the 
> luminaire is listed in the cut sheet as being 53-5/8".  Which 
> dimension do I use to create the illum "enclosure?"

Whatever you need to enclose the geometry you create.

> I used the command:
> ies2rad -di -t white -i .56419 -o light2 d21998.ies
>
> and the resulting light2.rad file reads:
>
> # ies2rad -di -t white -i .56419 -o light2
> # Dimensions in inches
> #<IESNA:LM-63-1995
> #<[TEST] 21998
> #<[DATE] 05/31/2001
> #<[LUMCAT] AGDMWU232-F3-120-1/2-EB
> #<[LUMINAIRE] DAY-BRITE ADAGIO DIRECT/INDIRECT W/33-CELL SPECULAR 
> LOUVER
> #<[LAMP] F32T8
> #<[BALLAST] ADVANCE REL-2P32-SC
> #<[MANUFAC] DayBrite-Capri-Omega(Genlyte Thomas Group)
> #<[_TIFF_FILE_NAME] AGD2
> #<[_VERSION] fo2ies 2.01
> #<Reflection factor 0.92, Test distance = 26 ft.
> # 60 watt luminaire, lamp*ballast factor = 0.88
>
> void brightdata light2_dist
> 5 corr light2.dat source.cal src_phi4 src_theta
> 0
> 1 1364
>
> light2_dist illum light2_light
> 0
> 0
> 3 1 1 1
>
> light2_light sphere light2.s
> 0
> 0
> 4 0 0 0 0.56419
>
> ____
>
> I edit this file to use lboxcorr.  I convert inches to meters 
> (multiply inches by .0254).
> ...
> void brightdata light2_dist
> 5 lboxcorr light2.dat source.cal src_phi4 src_theta
> 0
> 4 .815 1.363 .305 .0921
> ...
> Question 3:  Because I used the -di option in the ies2rad command, I 
> thought that converting inches to meters was the way to go.  Should I 
> be converting feet to meters?

The A2, A3, and A4 arguments should be in meters.  Where did you get 
the 0.815 value?  I assume this is a lumen depreciation factor.

> ____
>
>
> Question 4:  When I replace the illum sphere with a box, should I be 
> using the units of my model (inches) or sticking with meters?  In 
> other words, should I be using:
>
> !genbox light2_light light2.s 1.363 .305 .0921 \
> 	| xform -t -.6815 -.1525 -.04605
>
> or
>
> !genbox light2_light light2.s 53.625 12 3.625 \
> 	| xform -t -26.8125 -6 -1.8125
>
> I have tried both, and when I used meters, my image is black.  When I 
> use inches, I get a reasonable image of my space.

You should use whatever corresponds to your -d? option -- inches in 
this case.  I would recommend generating the box in meters then adding 
-s 39.37 to your xform command to make it clear:

!genbox light2_light light2.s 1.363 .305 .0921 \
	| xform -s 39.37 -t -26.8125 -6 -1.8125

>
> Question 5:  Can the dimensions of the illum geometry be slightly 
> different than the dimensions defined for the lboxcorr function?  The 
> rounding required in converting back and forth between units would 
> inevitably result in some differences.
>

They should be close -- they don't have to be exact.

-Greg