low-iron glass for luminaires

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

>  I guess that part of the difference between a new acrylic lens and a
> glass one might be in the absorption in a standard glass containing
> iron. Using low-iron glass instead would add some 2 or 3 per cent to
> the luminaire efficiency, depending on the thickness of glass. Maybe
> the producers use low-iron glass from the AFG, but I doubt it.

Dear Scott Buchanan, 

I'd like to know, if any producer of lighting fixtures is using your
low-iron glasses (cut and then hardened) to enhance luminaire efficiency.  
I guess that 2 or even 3 per cent may be gained this way compared to
conventional greenish glass. It seems not much but, the competititon is in
scale of per cents only.

Another point is that using ordinary glass is a probable reason why fresh
acrylic sag lenses give a bit better initial luminaire efficiency. As I
belong to advocates of non-polluting lighting, I try to wipe out all
obstacles for using flat hardened glass instead of plastic bellys
(producing glare inevitably) for outdoor lighting fixtures.

Still another point are optical data for your solar glasses -- I mean the
``dispersion'' of direct light for both Solite and Solatex for various
angles of incidence. Such a slight dispersion might be an advantage to
limit glare from seeing directly the discharge tube of lamps. The images
at
  http://www.afgglass.com/products/viewbyfamily/solar/
 (the pdf files, mainly) are quite illustrative but I am not sure if for
angles of incidence about 70 degrees, the radia of the dispersion
cone would remain similar, i.e., about 1 degree for Solite.

Moreover, transmission values of Solite for acute angles (i.e., angles of
incidence over 50 degrees) for light and solar radiation are also
interesting for me. Light transmission for lighting fixtures, solar ones
for solar collectors. 

with best regards,
Jenik Hollan

PS. 
 I took part in assembling a largest solar collector in Czechia with a
selective absorber, 36 m2, directly on the roof this summer, and the
low-iron glass we have been using has been probably from you -- nobody
knew, but it came from Green One Tec from Austria, the (second?) largest
collector producer in the world, and looked quite similar to your Solatex
(or Solite?). Pitiously, I have no sample left, it's inside the roof
there now, so I cannot measure it myself. The pictures from the
installation (Czech text only) are at http://www.veronica.cz/tinox, if I
could add the origin of the solar glass, I would gladly do it.

(As regards outdoor lighting, my URL is http://www.astro.cz/darksky .)