Re: [DSLF] FS fixtures are vital for reducing sky luminance

[Jan Hollan <jhollan@amper....muni.cz>]

> I must say that I am somewhat a little sorry to read that you had already
> written to paper that I am working on :(  My calculations are also based on
> the formalism of Garstang but I minimize the burden of the computation
> by using a probalistic approach. Actually, my own program contain about
> 150 line of codes in mathlab!
> 
> May I get a copy of your paper to see if I should continue to work on my
> own paper.
>
> Regards, Yvan Dutil
 
Dear Yvan,

I did not write any paper yet and won't soon. Just the programme available
at http://amper.ped.muni.cz/light/ies2 (with example results for some
manufacturers) and those two remarks on its results (the recent one and
the old one given as an URL). So, please continue writing, if you would
employ my programme, I'd be happy. 

(I've noticed that apache on amper did not show the undispensable README
file in that directory, sorry, there is a symlink ``ReadMe'' now.)

The remarks missed an information that I've considered just single
scattering (unlike Cinzano et al.) -- adding a second scattering would
probably make the sky LP by direct light just above horizon even a bit
stronger. On the other side, statements on albedo and indicatrix type have
been misleading: albedo influence is simply a indirect proportionality (so
it _is_ important), indicatrix type is not very important (as I see now,
instead of relying on my memory). Diminishing zenith extinction makes the
sky LP proportion by non-FS luminaires a bit larger, namely for
non-changing CIE indicatrices (for the default one, the indicatrix has two
parts, the symmetric one from the gas always assumed to be responsible for
0.1 mag of zenith extinction). 

> As for the BRDF, I got  the CIE data. Unfortunately, they are almost
> useless for this peculiar application since the BRDF use by the lighting
> engineer are define only for grazing angle (<3 degres).

For obeying the road lighting standard it should suffice, as viewing
angles for CIE road-luminances-demands lie below 1.5 degrees (height of
the eye 1.5 m, 60 m from the first row of array points). IES demands
concern just viewing angle of 1 degree. (I take the values from the GE's
Aladan manual). The angles of incidence from the luminaires are to have
an almost full span (in the BRDF) to be useful, however. 

Of course, real roads are no CIE standards and it would be _very_
interesting to know their BRDFs (new and worn, in wet conditions as well).
And *.ies of old luminaires. The ones I've seen had their acrylic bellys
not much transparent any more.

If you would send me those available BRDF's, I could perhaps implement
them in my programme, so that it would be able to pick up the most
suitable fixtures for a given purpose (from thousands of possibilities). 
Next fortnight, maybe. And use them in Radiance (I'm slowly learning that
engine). 

clear view with no glare,
jenik