Improvements in Prism Lights.
Year: 1897

page_text: Date of Application, 4th May, 1897-Accepted, 3rd July, 1897
Improvements in Prism Lights.
I, FRANK CLEMENT SOPER, of No. 1410 Marquette Buildings, Chicago, County of
Cook, State of Illinois, United States of America, Gentleman, do hereby declare
the nature of my invention, and in what manner the same is to be performed, to
b particularly described and ascertained in and by the following statement:
My invention relates to prismatic glass and particularly to such as is designed
for use in windows and the like. Generally speaking, it consists of a plate of glass
with a series of prismatic ribs on one side thereof, said prisms being formed of
peculiar shapes so as to produce certain definite results. These prisms have either
refracting or reflecting surfaces or both refracting and reflecting surfaces. In the
ordinary prismatic glass these faces are plain surfaces, and are so formed as to
throw the light upward. In my present invention, I obtain the results I desire by
forming these surfaces either in whole or in part so that they will be curved or of
a particular angular relation, as is hereafter more fully described.
I have illustrated my invention in the accompanying drawings, wherein
Figure 1 shows an old form of glass, the lines showing approximately the action
of some of the rays of light which pass therethrough;
Figure 2 is a section through a modified form of my device;
Figure 3 shows a still further modification;
Figure 4 is a plan view of a glass tile embodying my invention;
Figure is a section through a part thereof;
Figure 6 is a section through a modified form of my device.
Referring now to Figures 1, 2 and 3 I have shown a form of glass having
prismatic ribs thereon, the surfaces being so formed and of such proportions as to
direct the light received into the apartment on substantially horizontal lines or
a little below the horizontal. The present construction produces this result with
the greatest possible certainty and with the least possible waste of light. I have
found that when the ordinary prismatic glass is used, 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 that 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. The ordinary prisms which
throw the light by refraction or reflection are very objectionable in many respects.
In Figures 1, 2 and 3 A is the body or the plate of glass, B, a series of prisms
thereon having each a face (and an inclined face D. As shown in Figure 1 these
faces are all plain. F is a ray of light bent in the body of glass as indicated at G
and again bent as indicated at H, this latter bend occurring as it issues from the
inclined face. Of course, the faces C C may be more or less inclined. J indicates
a ray of light which is received on the face C and is reflected away. Kindicates
e part of the prism which may be removed for certain purposes, thus giving more

page_text: or less of the incline to upper face of the prisms. In Figures 2 and 3, the action
of the curved surface is such that a large number of rays, as indicated, are directed
into lines not greatly departing from the horizontal and are thus in the first
instance prevented from being received upon and reflected away by the surface C,
even when that surface is elevated above the line of parallelism with the course
of light through the glass and in the second instance the action of the curve is such
as to distribute the light so as to cause equal quantities of light so to speak to fall
upon equal surface area at different distances from the window along a horizontal
line as indicated by the diagram lines L, L, L² L 3, L, L and L. This curve of
course can be varied and must be varied to suit different requirements. By vary
ing the curve somewhat, the light can be directed so that equal quantities of light
will fall upon equal horizontal areas at different distances from the window instead
of equal areas as indicated by the diagram of Figure 3. Moreover, the curves
should vary perhaps according to the direction from which the greatest quantity
of light to be transmitted is received. Under the conditions assumed in Figure 3,
the light to be received along the lines parallel with the ray and it being
intended to deliver substantially equal quantities of light over equal areas at
different distances from the window, the curve should be substantially as shown.
If the light is to be thrown into more nearly horizontal lines the surfaces C may
he less inclined than indicated in Figure 3 and may even he substantially
horizontal as indicated in Figure 2, but of course for most practical purposes the
light should be distributed somewhat below the horizontal lines and in such cases
with this improvement it might be desirable to have the upper surface C very
materially inclined with reference to the horizontal.
Referring now to Figures 4, 5 and 6, I have shown a construction wherein the
surfaces of the prisms have particular angular relations. As illustrated in these
figures, Alis the body of the glass having preferably a substantially,smooth surface B.
Care 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 1) 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,
, indicating the direction whence comes the greatest quantity of light, G, the direc-
tion 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
inclination 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 these 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, and
these angles I find in the case illustrated in Figure 5 to be substantially as follows:
substantially 70 degrees and K substantially 50 degrees.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:
1. A prism light for window illumination consisting of a body of glass having
a plain surface on one side and a series of prisms extending substantially across
the body of glass on the opposite side and having each two surfaces inclined to the
plane 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, the lower surface inclined to the plane

page_text: surface so that when the plane surface is substantially vertical the lowest light
received thereon is transmitted and directed into a substantially horizontal plane
2. A prism light for window illumination consisting of a body of glass naving
a plane surface on one side and a series of prisms extending substantially across the
body of glass on the opposite side and having each two surfaces inclined to the
plane surface so that the interior angle of the upper surface is 70° and the interior
angle of the lower surface 50º.
3. A prism light comprising a body of glass with a plane receiving surface on
one side and a series of prisms on the opposite side extending substantially across
the body, each prism having two faces, one a plane face and the other a curved
face.
4. A prism light comprising a body of glass with a plane receiving surface on
one side and a series of prisms on the opposite side extending substantially across
the body, each prism having two faces, one a plane face and the other a curved face,
said face inclined to the plane receiving surface.
5. A prism light comprising a body of glass with a plane receiving surface on
one side and a series of prisms on the opposite side extending substantially across
the body, each prism having two faces, one a plane face and the other a curved
face, the curvature being such that all the rays of light coming from a given
direction are transmitted so that equal quantities of such light fall on equal areas
taken at different distances from the prism light along a horiontal line and perpen-
dicular to the direction of the ray of such light delivered from the prism light.
6. A prism light substantially as herein set forth as and for the purposes
specified.
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.