[Radiance-general] Discomfort Glare - How do I evaluate

[Jan Wienold]

Hi Richard and rest of community,

we are actually working on a research project, dealing with user 
assessments with special focus on glare from daylight in office spaces.
We have already tested 100 subjects at two different locations under 
very different conditions (facade systems, window sizes, viewing 
directions...).

As a first result I can summarize, that all existing formula like dgi, 
ugr, cie, vcp show a pearson correlation less than 0.15. Values less 
than 0.5 can be also achieved by chance...
Therefore I can not advice you to use these indices.

I can already announce, that we will come up with a new, much more 
reliable index, which will be called " daylight glare probability dgp". 
This dgp will model the probability, that a person in an office will be 
disturbed by daylight glare. The publication on this will be submitted 
by me and Jens Christoffersen in few days to an special issue on 
daylighting in "energy and buildings" and will hopefully published end 
of this year.

Additionally, we will come up with a new tool called "evalglare" , which 
is based on the RADIANCE picture format and will be available in mid  of 
this year
This tool has some new features compared to findglare and will have the 
new index implemented, too. (see also 
http://www.radiance-online.org/radiance-workshop3/cd/Wienold_extabs.pdf). 
As soon as it will be available I will announce it.

In the meanwhile, I would chose the vertical eye illuminance as a 
measure for the glare - for this value we found reasonable results 
comparing this to the percentage of disturbed persons.

Jan


furry at ihug.com.au wrote:

>Hi all,
>
>I working on a glare study with reflected sunlight through a skylight causing 
>glare and we are evaluating different glass, laminates and meshes to mitigate 
>problems from the glare.
>
>When I use Radiance to evaluate each view, I can get the results for:
>- Guth Visual Comfort Probability,
>- CIE Glare Index (Einhorn)
>- Unified Glare Rating.
>
>What I would appreciate some advice on is which is the most appropriate in this 
>case for determining when glare has been reduced to a generally acceptable 
>level.  Also, I am wondering what values would be considered acceptable for 
>each of these 3 methods of determining glare (ie. VCP > 70% or 50% ??? .. what 
>is generally considered acceptable?).
>
>Thanks for your help,
>Richard
>
>
>
>
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>
>
>  
>

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  | \            Jan Wienold
                 Fraunhofer Institute for Solar Energy Systems
                 SOLAR BUILDING DESIGN GROUP - DAYLIGHTING
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