Improvements in Lenses for Lamps for Use on Velocipedes and other Vehicles.
Year: 1899

page_text: Date of Application, 12th Dec., 1899-Accepted, 27th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Lenses for Lamps for Use on Velocipedes and other
Vehicles.
I, JULIAN HENDERSON PITKIN, of No. 1291, Perry Street, in the City of Chicago,
County of Cook, and State of Illinois, United States of America, Master Mechanic,
do hereby declare the nature of this invention and in what manner the same is
to be performed, to be particularly described and ascertained in and by the
following statement:―
My invention relates to lenses for vehicle-headlights, and has for its object to
provide such a device that will assemble the rays of light and throw them in a
beam that shall be limited laterally to a narrow path and shall extend along the
ground from a point in close proximity to the source of light to a point consider-
able distant therefrom without at the same time crossing the line of the rider's
vision.
My improved lens is primarily intended for use on bicycles where a thoroughly
illuminated path from the wheel to a distant point ahead is essential in order
that the character of the road may be revealed to enable the rider to avoid
obstructions and consequent danger of injury, though it may be applied to any
vehicle-headlight. It is desirable in order to secure the best results that the
entire number of light-rays be utilized and concentrated throughout the path
to be illuminated, which in the ordinary bicycle headlight lens is not the case.
The objection to the lens in ordinary use is that it illuminates a wide angle
close to the wheel, while the road in front is left in darkness, thereby greatly
diminishing the probability of revealing an obstruction in the road to be travelled.
By my improved lens the road from immediately in front of the wheel to a
considerable distance ahead is thoroughly illuminated by a beam of light extend-
ing in a laterally-confined path, and any obstruction either close to or remote
from the wheel is quickly revealed. These desirable results are secured by
constructing the lens of vertical and horizontal prisms, the angles of refraction
of the latter being made to vary from the top to the bottom of the lens-that is,
each horizontal prism has a uniform refracting-surface of different angle from
that of other horizontal prisms, whereas the vertical prisms have each a refract-
ing-surface which in itself varies at different portions of the prism from top to
bottom of the lens, all as will hereinafter more clearly appear.
In the accompanying drawing, Figure 1 is a vertical section of the lens through
the centre thereof taken on line Figure 2.
Figure 2 is a front face view of the lens.
Figures 3 and 4 are horizontal sections of the lens taken on the lines A-B
and CD respectively. of Figure 2.
The lens is preferably rectangular, as shown in Figure 2, though it may be
six or eight sided or of any desired form, and is usually cast or moulded in one
piece for convenience of manufacture.
In constructing this improved lens advantage is taken of the well-known
property of the prism to deflect a ray of light as it passes therethrough first

page_text: toward the normal of the incident surface and then as it passes from the dense
medium of the prism into the less dense air, away from the normal of the emer-
gent surface. The direction of any ray of light may thus be controlled by
changing the angle of the prism through which it is caused to pass.
In the drawing the lens E, shown preferably as rectangular in shape, has any
usual form of centre S, either plane or convex, and is provided with horizontal
prisms a, a, a², a³, a², and a³, and with vertical prisms b, 61 and 62. The number
of horizontal and vertical prisms may of course be varied either more or less than
those shown.
By the terms "angle" and "inclination" as used in the specification I mean
the angle between the incident and emergent surface or the inclination of such
surfaces to each other.
The horizontal prisms a, a¹, a², a³, a¹ and a are constructed to have the
emergent surface ff of each at a different angle from that of the other horizontal
prisms, and this variation of angles is graduated successively from the top to
the bottom of the lens in regular order—that is, the lower prism a has its
surface ff of very slight inclination so that a ray of light from the source L
striking the incident surface e e¹ of the lens at will be refracted as it emerges at l¹
from the dense medium of the prism and intercept the ground in the direction
of a few feet only ahead of the wheel. The prism a is made with a slightly
greater angle of its emergent surface, so that a ray of light from L reaching the
incident surface at 18 will be refracted in the direction of 3 to reach the ground a
few feet ahead of the ray from prism a. Likewise the prism a² is constructed with
a slightly greater angle than the prism a', and for like reason its refracted ray 1
will reach the ground a few feet ahead of that from prism a¹, and so on regularly
to the top of the lens. Each successive prism has its angle slightly increased
in order to throw its emergent ray farther ahead, as prism a³ in the direction
of, prisma in the direction of 16, and prism in the direction of 17. The
effect of this regular variation in the angles of the horizontal prisms is that the
rays of light emerging therefrom will form a continuous path of light upon the
ground from a point close to the wheel to many feet ahead without at the same
time crossing the rider's vision.
i9
The vertical prisms 66 are arranged on opposite sides of the centre S and
are designed to refract the rays so, as to produce a parallel beam of light where
the rays intersect the ground, to thereby form a lighted path of uniform width
from the wheel to the distant point reached by the upper horizontal prism. To
this end the refracting-surface d d of each vertical prism varies in angle at
different parts thereof, and this for the reason that the rays refracted by such
prisms reach the ground at varying distances from the lens. The ray of light
emerging from the lower portion of the vertical prism is to reach the ground
at a point in close proximity thereto, for which reason the angle of the prism
at its lower part is slight, whereas the ray from the upper part of the same
vertical prism is to reach the ground many feet away, and therefore
the angle of the prism at that part is greater. This feature
well shown in Figures 3 and 4. Figure 3 represents a section of
the vertical prisms near the tops thereof on line A-B Figure 2.
and, as will be noticed. the angle of the emergent surface d d' of each of said
vertical prisms is much greater than the angle of the same surface nearer the
ground, as shown in Figure 4, which is a section on line C-D of Figure 2. In
other words, the emergent surface of each of the vertical prisms constantly
varies in angle from the bottom to the top to correspond to the distance the ray
of light has to travel before reaching the ground. If the angles of the emergent
surface of each of the vertical prisms were made uniform, the rays of light
emanating from the lower portion of the vertical prisms would perhaps be of the
desired width near the wheel; but the upper portion of the prisms would contract
the rays into a much narrower path as their contact with the ground became
more remote, whereas by varying the angle of the surface of each vertical prism

page_text: uniformly from top to bottom the lighted path is made of a uniform width
throughout.
"
Where the vertical and horizontal prisms meet, they are joined by a curved or
what may for convenience be termed a segmental" prism, as at c Figure 2,
and, as the angles of the horizontal and vertical prisms vary at their point of
meeting the segmental joining-prism is constructed with a varying angle suited
to harmonize at its points of meeting with the angles of the horizontal and vertical
prisms. Thus no abrupt change takes place in joining the two sets of prisms
and the pencils or rays of light are not interrupted and no dark areas are formed.
The lens when in place is preferably inclined slightly to the vertical, as
indicated in Figure 1, in order to secure the greatest illuminating effect upon
the ground and prevent the rays from interfering in any manner with the rider's
vision.
I have shown the lens as substantially rectangular in form, and I have shown
the prisms as so arranged that they correspond substantially to the contour of
the lens illustrated in the drawings. Obviously, however, the contour of the
lens may be varied, other polygonal or other forms than the rectangular form
shown being used, and the prisms may, in such a case, be arranged to conform
to the contour of the lens or may be otherwise arranged, if desired. In any case,
however, the prisms, if horizontal, will vary in angle as between themselves,
in the manner herein before set forth, and if otherwise than horizontal, each
prism will itself vary in angle from bottom to top as herein before set forth.
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 lens for vehicle-headlights having a series of vertical prisms, and a series
of horizontal prisms varying in angle from the bottom to the top thereof, the
incident surface of such prisms being in substantially the same plane, sub-
stantially as described.
2. A lens for vehicle-headlights having a series of vertical prisms each of which
varies in angle from the bottom to the top thereof, and a series of horizontal
prisms varying in angle as between themselves from the bottom to the top of
the lens, substantially as described.
3. A lens for vehicle-headlights having a series of vertical and horizontal
prisms, and segmental prisms joining said vertical and horizontal prisms and
having varying angles, substantially as described.
4. A lens for vehicle-headlights having horizontal and vertical prisms, and,
segmental prisms joining the same, the varying angles of these prisms being so
arranged that a beam of light of uniform width and extended for a considerable
distance ahead is projected on the ground, substantially as described.
5. A lens for vehicle-headlights which is characterized by the provision of
prisms having a uniform incident surface and emergent surfaces of varying
angles so arranged as to project a beam of light of substantially uniform width
at an angle of downward inclination, substantially as described.
Dated this 12th day of December 1899.
HASELTINE, LAKE & Co.:
45, Southampton Buildings, London, W.C., Agents for the Applicant.