invention shown in the drawing, substantially at a right angle
in respect to the prism-bars, these lens-bars presenting outer convex
faces, as shown in figure 1.
In the present instance each of the
prism-bars has a plane face 3 and a curved or lens-like face 4, for
a purpose explained hereinafter; but other forms of prism bar may be
used without departing from the main feature of our invention.
The purpose of such lens-bars is to
materially increase the effective area of the source from which
the glass derives its illumination, lateral rays being caught and
transmitted by the convex surfaces of the lens-bars, which would be
lost by reflection from a flat surface or from a glass presenting
a considerable area of flat surface on the light-receiving side,
all of the rays, moreover, being refracted by the lens without that
interference with each other which is an objection to light-projecting
glasses in which some of the light is transmitted directly, while
other rays are refracted and reflected across the path of the direct
rays, thus causing interference which materially detracts from the
light-projecting properties of the glass.
The lens-bars also serve to cause
lateral diffusion of the light projected by the glass, and
thereby correspondingly increase the area which can be effectively
illuminated.
We wish to avoid all internal reflection
from the lens surface of the glass when said lens-surface is presented
to the incident ray, and for this reason the lens-bars are
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