Note: Descriptions are shown in the official language in which they were submitted.
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LD-8237
REFLECTOR LAMP
Background of the Invention
The invention is in the field of optical
reflectors and reflect~r lamps.
One general type of reflector lamp comprises a
concave reflector having a parabolic contour with
respect to a focal pointr so as to reflec* frontwardly
light emitted by a light source located at the focal
point. The cross-section of the reflector usually is
circular, the diameter thereof varying with the distance
from the Eocal point. Additionally, a cone of light
rays directly from the light source at the focal point
passr unreflected, through the front of the reflector,
the angle of this cone of rays being determined and
defined by the front rim of the reflector. The more
widely divergent light rays of the cone of rays, i.e.
the rays passing relatively nearer to the rim of the
reflector, have such a large sideways component of
direction so as to fall outside of the desired light
pattern and therefore are wasted. This waste of light
can be reduced, and the optical efficiency improved, by
making the reflector deeper ~longer) so that relatively
more of the light is re1ected in the desired direction
and the cone of non-reflected light is narrower thus
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reducing the amount of wasted divergent light~ However,
there are practical limitations on increasing the depth
of the re~lector, such as cost, weight and awkwardness
of using it. Also, with a given maximum diameter as the
reflector is made deeper~ the focal point moves closer
to the rear surface, which complicates positioning of
the light source and if the light source is a filament
there is accelerated blackening of the nearhy rear area
of the reflector due to evaporation of the filament
material (usually tungsten). This accelerated
blackening can be alleviated by providing a concave
recess at the rear portion of the reflector, which has
the drawback of reducing optical efficiency.
Reflectors have been designed having combinations
of parabolic and spherical shapes. For example, U.S.
patent No. 2,629,046 shows a reflector having a
parabolic front section, a spherical intermediate
section, and a spherical rear section. U.S. Patent No.
1,799,711 shows an automobile headlamp reflector having
a parabolic front section, a spherical intermediate
section, and a parabolic rear section, these sections
being tilted with respect to each other so as to have
diferent focal points~ Other re1ector shapes have been
proposed, such as an ellipsoidal reflector lamp as is
disclosed in U.S. Patent No. 4,041~344.
Summary of the Invention
Objects of the invention are to provide a
reflector, and reflector lamp, having improved optical
e~ficiency which permits a design having lower power
consumption, and to achieve this with a reasonably
compact lamp.
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The invention comprises, briefly and in a
preferred embodiment, a reflector, and a lamp having a
reflector, which has a parabolic fronk section, a
spherical intermediate section, and a parabolic rear
section, each of the reflector sections having the same
common focal point, the reflector sections being
dimensioned so that all light rays, or substantially all
light rays, which are reflected by the spherical
intermediate section from a light source positioned at
the focal point, are re-reflected by the parabolic front
section.
Brief Description of the Drawing
.
Fiyure 1 is a front view of a reflector lamp in
accordance with the preferred embodiment of the
invention.
Figure 2 is a cross section side view taken on
the line 2 2 of Figure 1.
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:: Description of the Preferred Embodiment
A preferred embodiment of the invention, as shown
in the drawing, comprises a reflector lamp having a
~: concave reflector 11 shaped to have a front reflector
section 12 which has a parabolic contour with respect to
a focal point 13, an intermediate reflector section 14
which has a spherical contour with respect to the focal
:25 point 13, and a rear reflector section 15 which has a
: parabolic contour with respect to the focal point 13.
: The cross-section of the reflector 11 perpendicular to
its principal optical axis is circular, as shown in
Figure 1. Thus, each of the three reflector sections is
deined by a surface of revolution of a parabolic or a
circular curve. A filament 16 is centered at the focal
point 13 and preferrably is located in or near the plane
17 of mutual truncation at the joinder of the front
section 12 and intermediate section 14, as shown in the
drawing.
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Alternative light sources may be employed ir. place of
the filament 16, 5uch as a halogen regenerative-cycle
incandescent lamp or an arc discharge lamp. A lens
means such as a shaped lens or cover plate ~0 may be
placed or sealed over the front opening o~ the reflector
11, to protect the reflecting surface and keep it clean,
and/or to modify the light pattern, and is required if
the light source is a bare filament 16 in the reflector.
The reflector 11 may be made of molded glass, its inner
surface being coated with aluminum or silver to provide
a reflective surface~ and the filament 16 preferrably is
made of tunysten and is mounted on a pair of lead-in
support wires 18, 19 of suitable material such as
molybdenum.
Light rays which emanate from the light source 16
at the focal point 13 and which strike the parabolic
front reflector section 12 , will be reflected in a
generally frontward direction, as indicated by the light
ray path 21. Similarly, light rays emanating from the
filament 16 and which strike the parabolic rear
reflector section 15, will be reflected generally
frontwardly, as indicated by the light ray path 22. A
certain relatively small amount of the light eminating
from the light source 16 is not re~lected by the
~ 25 reflector 11, and undesirably emerges through the front
; opening of the reflector in a divergant beam pattern, as
indicated by the light ray path 23. The relative amount
of this light depends on how far frontwardly the
reflector extends from the focal point
In aacordance with the inventiont the spherical
intermediate section 14-is dimensioned with respect to
the parabolic front reflector section 12 so that all, or
substantially all, of the light emanating from the light
source 16 and which strikes the spherical intermediate
section 14, will be reflected thereby in a direction so
as strike the parabolic front section 12 and be
re-reflected thereby in a generally frontward by
direction. For example, a light ray 26 emanating from
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the light source 16 at the focal point 13 of the
reflector, stri~es the intermediate spherical section 14
and is reflected back along its path and through the
focal point 13, and strikes the parabolic front
reflector section 12 and is directed frontwardly as
indicated by the light ray path 27.
A preferred method of designing the reflector, is
to first design the front section 12 and then design the
contour of the spherical section 14. Next, a line is
drawn from the rim 31, and through the focal point 13,
to the contour line of the intermediate section 14; this
point of intersection establishes the joinder plane 28
at the rear of the section 14 where it joins the rear
section 15. Thus the light ray 26' emanating from the
focal point 13 and which strikes the spherical
intermediate section 14 at or adjacent to its rear plane
28, will be reflected back along its path and through
: the focal point 13, and strikes the parabolic front
section 12 at or near its front rim 31 and is directed
frontwardly as indicated at 27l~
In scientific optical terminology, the breadth of
the parabolic reflector curve at the focal point 13 is
~: the latus rectum and is represented in the drawing by
the line 17 in Fig. 2, and the vertex is the point on
the rear surface directly behind the focal point 13.
~ . The vertex of the front parabolic section 12 is the
: point thereon that would be directly behind the focal
point 13 if the parabolic curvature were to be continued
behind the focal point 13. Thus the focal point 13 is
~30 relatively close to the vertex of the front parabolic
: :curve and is substantially farther ~rom the ve~tex of
the rear parabolic curve 15. The diameter of the
spherical intermediate section 14 is essentially equal
to the length of the latus rectum of the front parabolic
curve 12~
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Due to the elongated shape of the filament 16,
not all the light from different parts of the filament
is emitted at the focal point 13l and therefore, will be
refleccted at slightly different angles at any specific
point o the reflector. As a consequence not all of the
reflected light from the intermediate section 14 will
pass through the focal point 13. Therefore the optical
performance of the reflector will be somewhat degraded
from that which would be obtained from a hypothetical
point source at the focal point 13. In adddition, the
beam coming from the reflector may, as is the state of
the art for such lamps, be further modified by lenses
andjor diffusers to achieve a light distribution at some
distance from the lamp to meet the requirements for a
spot lamp or a flood lamp AS commonly conceived by the
lighting industry. It will remain true, however, that
the major portion of the advantages achieved with the
above described reflector with regards to a point source
will be realized with such an elongated filament and
with the customary lenses and/or means of light
diffusion.
The space defined and surrounded by the spherical
intermediate section 14 provides a recess for
accommodating the light source 16 r and spaces the
re~lecting surfaces at the back part of the reflector
sufficiently far way from the filament 16 to minimize
blackening thereof by evaporated filament material, and
the invention accomplishes this while retaining an
optical efficiency substantially as good as if the
entire reflector had a single parabolic curvature.
Since the invention provides a reflector
construction in which all of the light reflected by the
intermediate section is re-reflected in the desired
frontward direction by the parabolic front section, and
is not "lost" by passing beyond the front face in a
divergent pattern, the improved optical efficiency
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permits construction of a lamp requiring lower watts of
- power for a given amount of useful light, thus
contributing to the nation's goals of fuel economy.
Whilè preferred embodiments of the invention have
been shown and described, various other embodiments and
modiications thereof will become apparent to persons
skilled in the art, and will fall within the scope of
the invention as defined in the following claims.
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