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Handbook: 16 of 287
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In the Window Plate and Forilux the character
of the installation does not end with the mounting of the prisms; but the
prism lenses themselves are manufactured in great variety of shapes
and with widely differing surface patterns and effects. Innumerable
combinations of these single lenses in surface patterns, bands and lines
may be made.
In nearly all of the prescriptions of Luxfer
Prisms which are found in the table headed "Luxfer Prism Prescriptions,"
more than one kind of prisms are used. Those which are indicated by
the heavy type form the body of the plate and throw the light into the
main part of the room. We call these the MAJOR PRISMS.
The other one or two prisms designated by a lighter type, are designed
to throw the light in the front part of the room. We call these the
MINOR PRISMS. It is evident, therefore, that from any
one particular point in the room the prism plate will be shaded in
some parts, because some prisms throw the brightest light in one
direction and others the brightest light in other directions. This
gives an opportunity to the architect to place a design in his window,
and this design is seen very clearly both from the inside and from
the outside. In the back part of the room in general, the major prisms
of a plate, indicated by heavy type, are very bright, while the prisms
indicated by the lighter type are darker. In the front part of the
room the reverse takes place, the minor prisms being very light and
the major prisms darker. On the outside of the window the minor prisms
are usually several shades brighter than the major prisms. A few of
the designs which have been used with satisfaction in Luxfer Prism
plates are shown by the illustrations.
A Canopy differs from a Forilux in that
the plate of prisms is fastened at its upper edge to the wall over the
opening, the lower edge lifted until the proper angle for best receiving
the light is secured, and it is then fastened in this position by chains
or brackets as the conditions may require.
The prism lenses used in a canopy are of a heavier
nature than those used in a forilux, and the construction of the frames
and supports much heavier and more complicated, as they are oftentimes
so constructed that they may be closed or lifted entirely.
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