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
UGR should be <=20
VCP >= 67
All glare ratings are related.
UGR is most widely used. It would be appropriate for small skylights.
The Glare Index System was used in Great Britain, Belgium, South Africa and (slightly modified) in Scandinavia. As a recommendation, nowhere in the visual field should the luminance of any bright area exceed 40 times the luminance of the visual task.
Martin Moeck
···
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From: [email protected] [mailto:[email protected]]
Sent: Tue 1/18/2005 5:26 PM
To: [email protected]
Cc:
Subject: [Radiance-general] Discomfort Glare - How do I evaluate
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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Hi Richard,
o.k. then, let's open this can of worms:
Quoting from "Daylighting in Architecture - A European Reference Book",
the DGI is stepped as such:
Just imperceptible 16
18
Just acceptable 20
22
Just uncomfortable 24
26
Just intolarable 28
It seems to me that you definitely shouldn't be using the UGR or any other
non-DGI, because they are all derived for artificial light sources. Having
said that, although the DGI is the only GI available now for natural
lighting (windows, sky lights etc.), more recent research has shown that
it's hardly applicable. So while artificial GIs might hold true to some
extend, daylight GIs should be treated with much scepticism and asbestos
gloves. You are pretty much on your own here, there is no generally
accepted theory. The DGI is the best we have at the moment, but there is
much debate about it.
I would suggest that you look at the contrast ratios of the surrounding vs
the reflected sun light and try to make the best of it. Glare is also much
more tolerated when it's not directly in the direct field of view.
Although not true in your case, you'll find that DG is much more tolerated
and glare from artificial light sources because usually it goes
hand-in-hand with a view out of the window which causes glare, and this
can not be quantified in a formula. There are just too many physiological
and psychological aspects that play a role here to make this an "exact
science".
Sorry for giving such a hard time, but it ain't easy.
To bring up a more "holistic" point of view: if you have bright sun
patches, then it's more likely that you should be worried about
overheating than glare. The latter costs you money in terms of A/C, the
former is a nuisance, not a problem, if caused by daylight.
Cheers
Axel
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
[email protected] 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
_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general
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o - > \ Jan Wienold
Fraunhofer Institute for Solar Energy Systems
SOLAR BUILDING DESIGN GROUP - DAYLIGHTING
Heidenhofstr. 2 79110 Freiburg
GERMANY
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