Prismatic Window Lights with the Prisms Placed at a Predetermined Angle.
Year: 1897

page_text: Date of Application, 13th July, 1897-Accepted, 4th Sept., 1897
COMPLETE SPECIFICATION.
Prismatic Window Lights with the Prisms Placed at a Predetermined
Angle.
I, JOHN 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:-
My Invention relates to prismatic lights, especially such as are intended to
receive light at a window and direct it into an apartment substantially on horizon-
tal lines, or a little below the same. My object is to make prismatic ribs of such
proportions as to accomplish this result with the greatest possible certainty and
with the least possible waste of light, so to speak, on the glass. It is found that in
case of the use of prismatic lights of the general construction of those shown herein,
the appearance of the plate or complete window glass is frequently striped; that
is, there are alternate bands of black and white or dark and light. The ideal form
of this glass is one in which whether or not this peculiarity is present there shall
be transmitted through the glass the greatest possible amount of light, and in which
the greatest possible amount of light shall be directed into substantially horizontal
lines or into those parts of the apartment where the light is most needed. For
example, a prism which throws the light upward by refraction or by reflection is
objectionable to a degree.
My Invention is illustrated in the accompanying drawings, wherein,
Figure 1 is a plan view of a glass tile.
Figure 2 a section through a part thereof.
A is the body of the glass having preferably a substantially smooth surface B.
CC are prisms or prismatic ribs, on the opposite side of the glass. Each prism has
two surfaces D and E, and, of course, the action of the prism on the light is
determined by the inclination of these two surfaces. I have found that the most
satisfactory results for certain purposes are obtained when the surface D is placed
substantially parallel with the direction through the body of the glass of those
rays of light which come from the lower part of the powerful source of light. This
is indicated by the light ray F G H, which is taken as an ideal ray, F indicating
the lower direction whence comes the greatest quantity of light, G the direction
which such light takes through the body of the glass and which is therefore
parallel to the face D, and H the substantially horizontal direction which the ray
of light takes in the apartment, and which is determined, of course, by the inclina-
tion of the face E. These angles, of course, vary with the direction of the entering
light, and also with the inclination of the surface B. The angle of the surface D
is indicated at J, and the angle of the surface E is indicated at K. I find that
the best form of this glass for certain purposes is that wherein those faces are
inclined to each other and the prisms are located so that the angle J is equal to
the complement of the angle K, plus an angle whose sine is substantially two
thirds the sine of the sum of the angle K and the angle of inclination of the face B,

page_text: and these angles I find in the case illustrated in Figure 2 to be substantially as
follows: J substantially 70 degrees and K substantially 50 degrees.
Having now particularly described and ascertained the nature of my said In-
vention, and in what manner the same is to be performed, I declare that what I
claim is:
-
As a new article of manufacture, a prism light for window illumination con-
sisting of a substantially flat body of glass having a receiving surface on one side
and a series of prisms systematically arranged to produce an increased illuminat-
ing effect in the apartment, extending substantially across the opposite side of the
body of glass, such prisms having each two surfaces inclined to the receiving
surface so that the interior angle of the upper surface is equal to the complement
of the interior angle of the lower surface plus the angle whose sine is two thirds
the sine of the lower angle, and such lower surface being inclined to the receiving
surface so that when the receiving surface is substantially vertical the lowest light
received thereon is transmitted and directed into a substantially horizontal line,
substantially as shown and described.
Dated this on day of July 1031.
For the Applicant,
W. LLOYD WISE,
46 Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.