Prism Lights for Windows having Primary and Secondary Prisms.
Year: 1897

page_text: Date of Application, 13th July, 1897-Accepted, 21st Aug., 1897
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COMPLETE SPECIFICATION.
Prism Lights for Windows having Primary and Secondary Prisms.
I, JOIN MEIGGS EWEN, of No. 1129 The Rookery, Chicago, County of Cook,
State of Illinois, United States of America, Mechanical Engineer, do hereby
declare, the nature of my invention and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement:-
707
-1.1
My invention relates to prism lights such as are intended to be afterwards
assembled in a series to form a prism plate. Many of these prism lights and
plates are adapted to be used either as reflectors or refractors; but in some cases
they are desired for refracting only; and there are other reasons for departing
from the usual forms of such prism lights, as will be hereinafter explained.
My invention is illustrated in the accompanying drawings, wherein
Figure 1 is a plan view of my improved prism light.
.
Figure 2 is a section therethrough.
Figure 3 is an enlarged detail section to illustrate more fully the action of
the prism light on the rays of light which fall upon it. The latter figure also
illustrates the distinction between the present invention and previous forms of
prism lights.
Like parts are indicated by the same letter in all the figures.
Each
A is the body of the prism plates; B B, the primary prisms thereon; C C,
the secondary prisms formed on one face of the primary prisms. These primary
prisms have each two faces, one the face 1), which is substantially a plane surface,
and the other, the face which is broken up by the secondary prisms.
secondary prism has two faces, one the face E, parallel with the face D, and the
other the face F, which is approximately at right angles to the plane surface G
of the prism light, "or parallel to the line of vision; that is, parallel to the
direction which the light is to take from the prism light to the point where the
illuminating effect is to be secured. This ordinarily is a line approximately at
right angles to the receiving surface of the prism light.
Referring now to Figure 3, H H¹ illustrate what I describe as low rays of light,
striking upon the surface G. J and J¹ I describe as high rays. The ray H strik-
ing the surface at the point H2 is deflected to the direction H3 and emerges from
the surface D, taking the direction H which is the desired direction, the parts
being drawn accurately. It is obvious that this ray therefore emerges from that
part of the prism beyond the dotted line H5, and therefore it is obvious that if
the part of the prism beyond the dotted line H5 were removed, that such rays
of light would not be properly refracted to reach the part of the room desired to
be illuminated. Taking now the ray J, or the high ray, we find that it strikes
the surface G at J, whence it proceeds in the direction J³, being refracted at J
to the direction J5, whence it is in part reflected into the direction J6
and is partly refracted into the direction J7 and reflected at J8
into the direction J. The lines on the drawing indicating the course of the rays
of light are not intended to be at all exact in position, but are simply designed
to diagrammatically illustrate what it is intended to convey. These several
parts, so to speak, of such ray are lost for the practical purposes of this prism

page_text: Under the
light. The last preceding attempts to trace the ray or its part, so to speak, is
simply designed to illustrate the fact that the best results may be obtained with
reference to high rays such as the rays J and J¹ when the part of the prism
beyond the dotted line H is removed. We are therefore confronted with con-
ditions which are antagonistic to each other, some rays calling for the removal
of this portion of the prism and others calling for its retention.
ordinary conditions of prism lights, it is found best, if not indeed essential, to
keep the surface K at a practically right angle, or in other words practically
parallel with the line of vision, the surface K having a certain elasticity, so to
speak, or descending to a certain degree below the exact right angle to what in
this art is known as a practical right angle. Now by considering the correspond-
ing high and low rays H¹ J, we find that by means of the secondary prisms
arranged as shown, the ray H¹ and of course all other such rays will be directed
into substantially horizontal lines, while the very high rays will be directed
into the room to be lighted, and will not be to any great degree lost. We can
therefore secure in a great measure the good results flowing from the removal of
that portion of the prism beyond the dotted line H5, without suffering the evil
results which would flow from its mere removal, by providing the secondary
prisms, substantially as shown, along the line of such removal; and this is the
substance of my invention.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what I
claim is:-
A prism light having a plane surface on one side and a prism surface on the
other, such prism surface composed of a series of primary prisms each having one
plane surface and a prism surface, such prism surface on the primary prism
being itself formed into secondary prisms, each having a face at right angles to
the plane surface of the prism light, and a face parallel to the plane surface of
the primary prism.