[Radiance-general] Evalglare - Luminance or Illuminance

[Jan Wienold]

Hi Andrew,

yes, evalglare needs a 180° fish-eye(-vta)- LUMINANCE image. Internally
it calculates the vertical illuminance as Greg mentioned before.

A value of 0.4756 is a rather high value (-> 48% are disturbed by glare).

At the last building simulation conference, I suggested some "glare
classes" based on user assessments, which may help to interpret the DGP
values.
(table 5 in http://www.ibpsa.org/proceedings/BS2009/BS09_0944_951.pdf ).
Further details can be found also in my dissertation "Daylight Glare in
Offices", which will be available in some days as pdf on our web-site.


Cheers,

Jan


Greg Ward wrote:
> Hi Andrew,
>
> You definitely want a luminance image -- using -i would give you wrong results.  Evalglare should add up luminances with the appropriate weighting to get vertical illuminance at the eye.
>
> Cheers,
> -Greg
>
>   
>> From: "Bissell, Andrew" <a.bissell at cundall.com>
>> Date: October 2, 2010 1:07:53 PM PDT
>>
>> Sorry for what must be obvious questions.  I have just compiled evalglare for Linux and I have run a few test images albeit the images were very low res.  I have read various papers and posts on the net and seen the images referred to as luminance images and illuminance images.  So which is it?  Part of me says luminance as brightness is more relative to glare, on the other hand my understanding of DGP is that it measures illuminance at the eye.  Which led to me confusing myself over the type of image required.  Certainly if you try both, the results are different, however the images I am using are crude with just 1 bounce so that could easily explain the difference.
>>
>>  
>>
>> Also I read the luxeuropa2005.pdf on the evaluation method etc.  However I was still at a loss as to what the DGP results really meant.  E.g. if the DGP result is 0.4756 what does that mean.  The document talked about levels below 0.2 not being reliable. 
>>
>>  
>>
>> The other evalglare posts were useful wrt –vth and –vta, also the picture header.  Thank you.
>>
>>  
>>
>> Regards
>>
>>  
>>
>> Andrew
>>
>>     
>
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-- 
Dipl.-Ing. Jan Wienold
Project Manager
Fraunhofer-Institut für Solare Energiesysteme
Thermal Systems and Buildings, Lighting and Daylighting
Heidenhofstr. 2, 79110 Freiburg, Germany
Phone: +49(0)761 4588 5133 Fax:+49(0)761 4588 9133
jan.wienold at ise.fraunhofer.de
http://www.ise.fraunhofer.de

In office: 
Mo,Tue: 8:30-18:00
We,Thu: 8:30-16:00
Fr:  8:30-15:30

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