[Radiance-general] Error: Rendering with Radiance p. 319 Luminaire Modeling

[Randolph M. Fritz]

But then, why did Chas say to specify the radius of a projected unit 
sphere in RwR?  The radius of the sphere does not seem to matter, at 
least in the case of the photometry I am working with.  Does it make a 
difference with other sorts of photometry?  Or…?

What am I missing?

Randolph

On 2012-02-07 01:40:29 +0000, Greg Ward said:

> Hi Randolph,
> 
> Whatever radius you give, ies2rad should adjust the brightness to keep 
> the total lumen output the same.
> 
> Best,
> -Greg
> 
>> From: "Randolph M. Fritz" <RFritz at lbl.gov>
>> Date: February 6, 2012 4:45:53 PM PST
>> 
>> On 2012-02-07 00:18:26 +0000, Randolph M. Fritz said:
>> 
>>> On 2012-02-07 00:12:18 +0000, Greg Ward said:
>>>> Hi Randoph,
>>>> Could you be more specific?  The radius of a sphere whose *projected*
>>>> area is 1.0 for any distant point is sqrt(1/pi) as Chas derived it.
>>>> This is in fact what ies2rad needs.  This is not the same as a sphere
>>>> whose total surface area is 1.0, which is the value you derived.
>>>> Is there an error in ies2rad.c, somewhere?
>>> Then maybe I've done something else wrong.  When I ran a simulation
>>> which checks the luminaire model against the IES file by simulating a
>>> goniophotometer the numbers lined up.  I'll take a closer look at my
>>> scripts and see if I can find a factor of two somewhere.
>> 
>> The same check script worked correctly with an untouched ies2rad output 
>> file with both the given geometry and a spherical substitute.
>> 
>> I then ran the procedure with -i 0.56419 and the numbers I am getting 
>> back are the same and correct.
>> 
>> I am now thoroughly confused.  Does the radius even matter in that 
>> procedure?  Or do I have a case of a luminaire where it doesn't matter?
>> 
>> Randolph


-- 
Randolph M. Fritz