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

[Axel Jacobs]

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