[Radiance-general] Re: direct/indirect photometric

[John An]

>
> Date: Tue, 27 May 2003 09:43:33 -0700 (PDT)
> From: Charles Ehrlich <ckehrlich@yahoo.com>
>
>
> Greg and John An, Unless the new version of Radiance is significantly 
> different that when I wrote chapter 5, I do not think that you need to 
> change A1 if you follow the method described in the book.  The method 
> was specifically designed to address linear sources.  It is also the 
> method employed in the luminaire editor in Desktop Radiance. Is it 
> still true that the "lboxcorr" function automatically corrects for the 
> surface area of the emitter?  If not, then we have a major re-write on 
> our hands for the new edition. -Chas
>

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?

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?"


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?
____


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.

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.




Thanks again.


John