Page 46 - Between light and shade

between light and shade, TRANSPARENCy and reflection

Brussels, where large panes of glass with a semi-
reflective pyrolitic coating reflect light coming
from the North into the offices, without obstruc-
ting the view [01/381, Fig. 26].

Ultimately, even ordinary glass always reflects
something 34.

natural light sensors
Other recent technological developments are
paving the way for new ways of transporting
natural light, with or without concentrating
it. This is the reason why we now have sensors
made from shells, in the form of segments of
paraboloids of revolution, with an axis that always
points towards the sun, concentrating the sun’s
energy on a single point (the focal point of the
parabola). At this point, the visible fraction of
the energy is transferred via a fibre optic bundle

34 Apart from glass with an “anti-reflective” coating. The decline
in reflection from old panes of glass was observed for the first
time by John W. Rayleigh, in 1887. The first anti-reflective
coating, which was unreliable, was discovered by Harold
D. Taylor in 1896, and patented in 1904, again in England. It was
not until 1935 that Aleksander Smakula at Carl Zeiss patented
the first reliable process, and until 1990 for 99.5% transmission
to be achieved.

The most effective current anti-reflection coating is produced
by Schott with the brand name “Amiran”. It has a visual reflec-
tion level of 1% for single glazing and 2% for double glazing,
compared to 8% and 15% respectively for “untreated” glazing.
This level rises to 20% for triple glazing!
46