Improvements in Prismatic Lights.
Year: 1897

page_text: Date of Application, 4th May, 1897-Accepted, 10th July, 1897
Improvements in Prismatic Lights.
I, WILLIAM STORRS MACHARG, of No. 1410 Marquette Building, City of 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 per-
formed, to be particularly described and ascertained in and by the following
statement:
My invention relates to glass tile or window glass, such as is commonly described
under the title of prismatic lights. The object of such glass is to receive the light
and distribute it in the apartment to be illuminated in a manner different from
that in which it would ordinarily be distributed where ordinary glass is used, or
where there is no window glass. The effect of window glass or windows having the
ordinary glass on the reception and distribution of light in the apartment to be
illuminated is considerably varied owing to the shape and position of the shaft,
alley or street from which the light is received. For example, if the window be
in a building rising free from all surrounding obstructions, or, in other words, a
considerable distance from other buildings, it is plain that the angle of reception
of light will be very large, for example, approximately ninety degrees, that is to
say, that some of the rays of light passing through the window and tending to
illuminate the apartment will be derived from all parts of the angle of ninety
degrees, the greater number of such rays, of course, being derived from perhaps
the middle half of such ninety degrees. This is so because the rays which fall
approximating the vertical are reflected away by the window glass in large
numbers, whereas, there is a comparatively small number of rays of light travelling
horizontally to their surface. Now, if on the opposite side of a comparatively
wide street a series of high buildings be erected, it is evident that the greater
portion of this angle of reception of light or angle of supply of light has been
cut off, and it is clear as the buildings on the opposite side of the street ard
increased in height, or as the street is diminished in width, the angle through
which the light is received will be diminished until finally, under certain con-
ditions, as for example, in very narrow streets or alleys or courts or air shafts,
and particularly where high buildings are on the opposite sides of such spaces,
the light received against the glass will be almost wholly reflected away from it
and the only light of any consequence passing through the window will be the
light generally diffused through the atmosphere outside of the window and thus
passing through the glass. Now, in the use of prismatic lights it is found
impracticable to make very excessively deep or heavy prisms from various
difficulties which will readily occur to any one familiar with this subject, and,
moreover, in the practical use, supply and sale of such devices, it is desirable of
course to have uniform sizes and thicknesses and so far as may be possible, uniform

page_text: shapes of all the prisms. In the conditions above referred to, however, it is
desirable that the prismatic glass should be so arranged as to introduce the greatest
amount of light, or in other words, so as to reflect away from the exterior of the
glass the least amount of light possible under practical conditions. These con-
ditions vary, of course, though ordinarily within certain reasonable and well
define limits, and the particular configuration of the receiving surfaces and the
prisms proper must vary, but a few general types must answer practically for all
ordinary conditions. In my drawing, therefore, I do not pretend to more than,
as it were, diagrammatically suggest or illustrate the idea without attempting to
give all the forms, or, indeed, any necessary form of the glass. I have, however,
desired to illustrate my invention in connection with prismatic glass, such as is
now in more or less extended use.
Figure shows a cross section through a prismatic glass or tile such as can be
used to make up a window glass having a flat or plane exterior surface;
Figure 2 shows a similar glass with a series of receiving surfaces on the formerly
flat surface opposite each prism:
Figure 3 shows longer receiving surfaces;
Figure 4 shows shorter receiving surfaces;
Figure 5 is a diagrammatic illustration of an alley or shaft with a window at
the bottom equipped with my improved light, and dotted lines showing the course
of the light, and also showing the construction of the glass, if my improvements
were omitted, the difference in the reflecting power of such glass being illustrated
by the dotted lines running off to the ground. The same thing is shown on a
larger scale in Figure 3.
No attempt has been made to adhere to the absolutely correct angles of the glass
surfaces or angles of reflection, but as previously suggested I am simply trying
to illustrate the idea.
Referring to the figures, like parts are indicated by the same letter in all the
figures. A is the body of the glass, having in Figure 1 the smooth surface B;
in Figure 2 the receiving surface C; in Figure 3 the receiving surface D; in
Figure 4 the receiving surface E. F is a building, Ga building on the opposito
side of the alley or court H. and J, the receiving surface of the window at the
bottom of such shaft or court K are the prisms, which in this case act as refracting
prisms.
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 comprising a body of transparent material substantially in
the form of a plane with prisms on one side inclined at an angle to the plane of
the glass so as to receive and refract light which would otherwise be reflected off
from a plane surface, and substantially parallel prisms on the opposite side of
the glass adapted to again refract the light so as to deliver it in the desired
direction, the angles and arrangement being such that substantially all the light
passing through is sent in the same direction.
2. A prism light consisting of a substantially flat body of transparent material
with prisms on its opposite side substantially parallel to each other and extending
substantially across the body of glass, said prism shaped so that the light delivered
upon the receiving surface is successively refracted in the same direction, the
angles and arrangement being such that substantially all the light passing through
is sent in the same direction.
3. A prism light comprising a body of transparent material substantially in the
form of a plane with transverse substantially parallel prisms on its opposite side
extending substantially across the body of the glass, the angles and arrangement
being such that substantially all the light passing through is sent in the same
direction.

page_text: 4. A prismatic light as herein described operating as and for the purpose
specified.
Dated this 4th day of May 1897
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.