IMPROVEMENTS IN LENSES FOR USE IN PAVEMENT LIGHTS AND IN OTHER SITUATIONS
Year: 1881

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane, in the
County of Middlesex, Patent Agent, for an Invention of "IMPROVEMENTS
IN LENSES FOR USE IN PAVEMENT LIGHTS AND IN OTHER SITUATIONS."
A communication from abroad by Peter Collamore, of Boston, in the County
of Suffolk, and Ninian Boyle, of Springfield, in the County of Hampden, both
in the State of Massachusetts United States of America.
PROVISIONAL SPECIFICATION left by the said Alexander Melville Clark at
the Office of the Commissioners of Patents on the 31st August 1881.
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN LENSES FOR USE IN PAVEMENT LIGHTS AND
IN OTHER SITUATIONS." [A communication from abroad by Peter Collamore, of
Boston, in the County of Suffolk, and Ninian Boyle, of Springfield, in the County
of Hampden, both in the State of Massachusetts, United States of America.]
These improvements relate to the lenses or prisms of pavement and other lights
used in pavements, vault covers, and in other situations.
Lenses have heretofore been made for such "pavement lights" of simple flat
form and also in the form of prisms for the purpose of reflecting or scattering the
rays of light to the greatest possible extent, but heretofore such results have not
been perfectly obtained on account of the limited area of reflecting surface and
the absorption of the light by the prism.
The object of this Invention is to increase the quantity of light, and to project
the same over a wide extent of surface, so that the illumination instead of being
limited to the direct light due to the superficial area of the lenses, minus the loss
by refraction, is increased and diffused to the greatest possible extent.
The Invention consists, first, of an illuminating lens of semi-prism form, and
having an extensive reflecting surface in comparison to the quantity of material
used; and, second, in the combination with such lens of metal spurs for preventing
slipping and to prevent abrasion of the exposed surfaces, as hereinafter described.

page_text: In the accompanying Drawings Figure 1 is a longitudinal section of the improved
lens as fitted in the frame of a pavement light; Figure 2 is a top view of the lens,
and Figures 3, 4, and 5 are elevations showing modifications in the form of the
lens.
A is a portion of the frame of the pavement light or vault plate. The lens or
semi-prism B is formed with a flanged top portion or head a, which may be of
circular or angular form, and fits in a rebated opening in the frame or plate A.
The upper surface is preferably formed, as shown most clearly in Figure 2, slightly
raised at the centre, and with radiating grooves having bevelled sides 6 formning.
facets so as to increase the extent of surface. The bevelled surfaces or facets being
depressed are protected from abrasion.
The upper surface may however be of simple conical form, as in Figure 4, or in
At the centre
certain situations a plain flat surface, as in Figure 3, may be used.
of the upper surface a metal spur or spurs C is fitted in a recess in the lens so as
to project slightly therefrom to prevent slipping and protect the surface.
The frame A is formed with pointed or other knobs or projections & between the
lenses, so as to keep the feet of persons walking over the frame entirely off the
lenses and prevent slipping. From the head a the lens projects downward in form
of a tongue h. This downwardly extending portion may be described generally as
a semi-prism, having an inclined flat reflecting surface e and an inclined back
surface f, that may be flat or nearly flat, convex, or concave, but is inclined in the
same direction as the reflecting surface e.
The angle of the surface e will vary according to location, and is of the first
importance. For a pavement light, as shown, it should be slightly less than 45° to
the plane of frame A. It is lengthened by the inclination in the same direction of
the back surface f from the head a to the lower point, so that while only a limited
amount of material is used, thereby saving weight and loss of light, an extensive
reflecting surface is obtained at the proper angle.
The frame A can be placed in a horizontal, vertical, or inclined position, the angle
of the semi-prism being varied to correspond. The lenses shown in Figures 3 and 5
are adapted for a vertical frame as a substitute for a window, in which case the
_semi-prism will be at the outside, as shown. The lenses can also be formed in
clusters instead of singly for certain locations.
With these lenses the light is magnified greatly in strength, and a soft diffusive
light obtained which is superior to direct sun light for most purposes. These lenses
are especially useful where only an indirect light is to be had, as such light is
concentrated and strengthened instead of being partly cut off. The lenses may also
be used with great advantage for gas chandeliers and in connection with the electric
light. In all cases the reflecting surfaces glow with a silver white light most
agreeable to the eyes. For particular situations the lenses may be plain or corru-
gated, waved, or angular on the reflecting surface, and they may be coated with
sterling silver or other reflecting substances.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alexander Melville Clark in the Great Seal Patent Office on the
27th February 1882.
"
ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent. "IMPROVEMENTS IN LENSES FOR USE IN PAVEMENT LIGHTS AND
IN OTHER SITUATIONS." A communication from abroad by Peter Collamore, of
Boston, in the County of Suffolk, and Ninian Boyle, of Springfield, in the County
of Hampden, both in the State of Massachusetts, United States of America.
These improvements relate to the lenses or prisms of pavement and other lights
used in pavements, vault covers, and in other situations.
Lenses have heretofore been made for such "pavement lights" of simple flat
form and also in the form of prisms for the purpose of reflecting or scattering the
rays of light to the greatest possible extent, but heretofore such results have not
been perfectly obtained on account of the limited area of reflecting surface and the
absorption of the light by the prism.
The object of this Invention is to increase the quantity of light, and to project
the same over a wide extent of surface, so that the illumination instead of being
limited to the direct light due to the superficial area of the lenses, minus the loss
by refraction, is increased and diffused to the greatest possible extent.
The Invention consists, first, of an illuminating lens of semi-prism form, and
having an extensive reflecting surface in comparison, to the quantity of material
used; and, second, in the combination with such lens of metal spurs (or metal or
glass knobs) for preventing slipping and to prevent abrasion of the exposed surface,
as hereinafter described.
In order to make the Invention communicated to me readily understood, I will
proceed to describe the same by reference to the accompanying Drawing, in which
Figure 1 is a longitudinal section of the improved lens as fitted in the frame of a
pavement light; Figure 2 is a top view of the lens, and Figures 3 and 4 are
elevations, and Figure 5 is a section showing modifications in the form of the
lens.
A is a portion of the frame of the pavement light or vault plate. The lens or
semi-prism B is formed with a flanged top portion or head a, which may be of
circular or angular form, and fits in a rebated opening in the frame or plate A.
The upper surface is preferably formed, as shown most clearly in Figure 2, slightly
raised at the centre, and with radiating grooves having bevelled sides b forming
facets so as to increase the extent of surface. The bevelled surfaces or facets being
depressed are protected from abrasion.
The upper surface may however be of simple conical form, as in Figure 4, or in
certain situations a plain flat surface, as in Figure 3, may be used.
At the centre
of the upper surface a metal spur or spurs C is or are fitted in a recess in the lens
so as to project slightly therefrom to prevent slipping and to protect the surface, or
metal or glass knobs may be employed.
The frame A is formed with pointed or other knobs or projections & between the
lenses so as to keep the feet of persons walking over the frame entirely off the
lenses and prevent slipping. From the head a the lens projects downward in form
of a tongue h. This downwardly extending portion may be described generally as
a semi-prism, having an inclined flat or concave reflecting surface e and an inclined
diffusing surface f, which may be flat or nearly flat, but preferably convex, as
shown; it is inclined in the same direction as the reflecting surface e.
The angle of the reflecting surface e will vary according to location; it is of the
first importance, and constitutes an essential feature of the Invention.
For a
pavement light, as shown, it should be slightly less than 45° to the plane of the
frame A. It is lengthened by the inclination in the same direction of the diffusing
surface from the head a to the lower point, so that while only a limited amount

page_text: of material is used, thereby saving weight and loss of light, an extensive reflecting
surface is obtained at the proper angle.
The frame A can be placed in a horizontal, vertical, or inclined position, the angle
of the semi-prism being varied to correspond. The lenses shown in Figures 3 and 5
are adapted for a vertical frame as a substitute for a window, in which case the
semi-prism will be at the outside, as shown in Figure 5, in which A shews a portion
of a double metal sash suitable for fire proof work; the lens B is bedded in putty.
The two parts forming the frame are rivetted or screwed together, so that in case
of fire the lens will be prevented from falling out when excessive heat has melted
the cement. When the lenses are employed with single frames it is preferred to
set them in lead. The lenses can also be formed in clusters instead of singly for
certain locations, as will be understood. To keep the lenses from becoming
covered with moisture, frost, or ice, any suitable means of ventilation may be
employed.
With these lenses the light is magnified greatly in strength, and a soft diffusive
These lenses
light obtained which is superior, to direct sun light for most purposes.
are especially useful where only an indirect light is to be had, as such light is con-
centrated and strengthened instead of being partly cut off. The lenses may also
be used with great advantage for gas chandeliers and in connection with the electric
light. In employing these lenses in connection with artificial light, and particularly
with the electric light, I employ a plate or bowl of lenses so arranged with regard
to the light or lights as to throw the light in the direction required, a suitable
reflector being placed above the light or lights; or the lenses may be also placed
above and at the sides of the light or lights. In all cases the reflecting surfaces
glow with a silver white light most agreeable to the eyes. For particular situations
the lenses may be plain or corrugated, waved, or angular on the reflecting and
distributing surfaces, and the reflecting surface may be coated with sterling silver
or other reflecting substances.
I am aware that pyramidal and other shaped lenses have been used, but they
concentrate the light too much and diffuse it too little or improperly. They decrease
instead of increasing the quantity of light admitted, while these greatly augment
the-light-which-would naturally_come through a given aperture.
Having thus described the nature of the Invention communicated to me, and the
best means I am acquainted with for carrying the same into effect, I would have it
understood that what is claimed and intended to be protected by the herein in
part recited Letters Patent is,―
Firstly. The manufacture and use of the herein described improved lenses or
semi-prisms for illuminating purposes, whereby the light (whether natural or
artificial) may, through the refracting medium of the lenses or semi-prisms
(or modifications thereof), be reflected at any angle and from any position, the
said lenses or semi-prisms being constructed as herein before described and repre-
sented in the accompanying Drawing, or any mere modification thereof.
Secondly. The central spur c or its equivalent projecting up above the said face,
in combination with projections & on the lens-frame, as and for the purpose set
forth.
Thirdly. The semi prism B having its downwardly extending tongues inclined
on the back face f, as and for the purpose specified.
In witness whereof, I, the said Alexander Melville Clark, have hereto set my
hand and seal, this Twenty fifth day of February, in the year of our Lord
One thousand eight hundred and eighty two.