[Radiance-general] glare dgi

[Phillip Greenup]

Pillo,

you are right that the UGR is designed only for artificial lighting glare 
considerations.  theoretically speaking, it can't be applied to assessment 
of discomfort glare from windows.  there are two reasons.  firstly, the UGR 
assumes the light source is very small (<0.01 sr) in the field of 
view.  because windows occupy a larger portion of the field of view, they 
have a greater impact on the eye's adaptation level, disturbing the 
assumptions of the UGR.  secondly, there is generally greater tolerance for 
mild degrees of glare from windows than from artificial luminaires.  this 
means that the UGR will overestimate the degree of perceived glare from 
windows.

given credit where it is due, most of this info came out of the thesis of 
Martine Velds from Delft, 'Assessment of lighting quality in office rooms 
with daylighting systems'.  the bad news is that she goes on to say that, 
'it seems to be infeasible to predict or measure the perceived degree of 
discomfort glare in a specific situation'.  she then went on to develop a 
new procedure called the 'visual comfort evaluation method', based on scale 
model or test room evaluations of glare.

so, this is not good news.  i'm afraid i don't have a better suggestion as 
i haven't spent much time on the problem myself.  there is, however, a good 
example of an approach taken by John Mardaljevic in the SIGGRAPH '98 course 
notes, available on the RADIANCE web-site.

Regards,
Phil Greenup.

At 04:11 pm 18/07/02 +0200, you wrote:

>tanks for the advice... i'll try CIE UGR...
>.. BUT it seems to me (=super lighting beginner ) that such index is intended
>for artificial lighting evaluation ONLY...
>i think cie is working to adapt UGR to daylighting purposes..
>
>let me know if you have further informations about
>
>
>tanks again!!!!
>
>pillo