[Radiance-general] calculating correct illuminance from irradiance

[Christian Fusenig]

Dear all,

i am new to Radiance and i went trough oodles of manual pages, R.w.R.- 
book, digest etc., but i couldn´t find an
answer to my question.
This is what i did:

1. I collected illuminance data for a *'Desisti' 1 KW* incandescent 
luminaire in our lighting laboratory.
2. I converted the illuminance values to luminance values and the color 
temperature of 3200K to RGB 1.377 0.913 0.351
-- I used the color temperatur conversion from the Radiance book p.431. 
I need to see the color temperature in the              pictures.
3. Finally i created an '.ies file' and used 'ies2rad' to get Radiance data.
-- Now i know, that instead i could have created  the' .dat ' file 
myself by dividing the luminance data by 179 lm/w --
4. I used 'rtrace' to measure my 'virtual' light source to verify my 
collected data
-- I used the same measuring distance as in the lab --
5.  My lamp ( source is a 'ring' ) is at 1 0 4 pointing downwards at 0 0 -1
6. at first i used 'rtrace' for the irradiance data:
*
       *echo "1 0 0 0 0 1" |rtrace -I -h lux_test.oct

/      4.154708e+01 2.754719e+01 1.059043e+01     
/*First question:  Are these irradiance values for RGB with the unit 
'w/square meter' ?*

7. now i measured the illuminance:


     $ echo '1 0 0 0 0 1' |rtrace -I -h  lux_test.oct |rcalc -e 
'$1=*47.4**$1+*120**$2+*11.6**$3'

         *5397.84338*  

-- this value is really satisfying, my collected data is *5400 lux!*

*Second question: Where do the factors of  *47.4/179 =* 0.26 , *120/179 
=* 0.67 and *11.6/179 =* 0.065 come from?

*I only know the standard factors from video for the EBU - Phosphors. 
There the luma value is: Y = 0.299*R+0.587*G+0.114*B
I tried these ones, but the result worse, in fact it is *5334 lux*.

Maybe someone can help me.

Best regards,

Christian

-- 
Christian Fusenig
Diplomand, Medientechnik
Undergraduate, Media Technology
Hamburg University Of Applied Sciences

address: Beim Schlump 27/07
              20144 Hamburg

email:    christian_fusenig at gmx.de

mobile:  ++49 179 5975845