Flashlight with an enhanced spot beam and a fully illuminated broad beam

A flashlight which selectively provides an enhanced spot beam and fully illuminated broad beam. The modified parabolic reflector produces with either a point source of light or an extended filament source of light a spot beam which is substantially more uniform across its disc as is produced by a conventional parabolic reflector, and a greatly improved broad beam without unilluminated areas. Further, the range of distance in which these effects are provided is importantly increased.

FIELD OF THE INVENTION 
This invention is a flashlight which can selectively project either a spot 
beam, or a broad beam that has no unilluminated regions, and which can be 
adjusted to reduce distortions which result from bulb filaments that are 
off of the axis of the flashlight's reflector. 
BACKGROUND OF THE INVENTION 
Persons, when in dark areas that are not provided with lighting 
installations, or if these are provided, then when there is a power 
failure, or in circumstances where the individual prefers not to turn on 
the lights, feel the need for a portable light-weight light source for 
localized illumination. With it, they can illuminate areas of concern for 
their own protection and guidance. The response to this requirement is the 
common flashlight or the directed-beam lantern. 
The most common flashlight is designed to provide a focused or small area 
beam, commonly called a "spot" beam. This is intended to be a relatively 
high-intensity beam with a limited area of illumination. Its preferred 
pattern, at least at its center, is a circular disc of reasonably uniform 
intensity. Another common objective is to provide a broader beam, that is, 
a beam with a larger illuminated disc. For the same luminous output from 
the light source, its intensity will be less than that of the smaller-area 
spot beam by the ratio of the two areas. 
For an ideal point light source, it is possible, of course, to design a 
reflector to produce a beam of any given desired diameter which is 
collimated and consequently does not increase with distance to the 
illuminated area. However, this requires a reflector configuration 
respective to each beam size. Furthermore, the parameters of such a 
reflector require an increasingly larger reflector as the diameter of the 
focused beam increases. These reflectors would be paraboloids of varying 
sizes. This requirement for larger size reflectors in order to produce 
larger size beams is a serious design limitation. In response, reflectors 
of various configurations have been suggested to produce broader beams 
with smaller reflectors by displacing the light source along the axis of 
the paraboloid. Still, the consequence of such designs has been a unique 
pattern at some established distance. At different distances, the pattern 
has undesirable variations and distortions since the reflected light rays 
are not parallel to the axis of the reflector. In general, such variations 
are often characterized by dark regions in the areas of the beam of 
greatest interest to the user. 
One further limitation of the conventional flashlight prevents the 
formation of an "ideal" spot beam that has the same diameter as the 
maximum diameter of the reflector. Conventional flashlights employ a 
polished surface paraboloidal reflector with a hole at the apex to 
accommodate the light bulb and bulb support structure. The result of 
having no reflecting surface near the centerline of the reflector is an 
unilluminated center disc when the point light source is positioned at the 
focus of the paraboloid. In order to illuminate the center area, the light 
source must be moved off of the focus and consequently produces a spot 
beam that has a larger diameter than the axis or diameter of the 
reflector. 
There remains to be provided a flashlight which can selectively produce, 
with a relatively small reflector, both a small spot beam and a larger 
area broad beam, with a reasonably constant luminosity across the beam in 
both beam configurations over a substantial range of distances. It is an 
object of this invention to provide such a flashlight. 
It should be kept in mind that the common flashlight has an incandescent 
filament and a concave reflector. Light emitted by the filament exits the 
flashlight in two modes. One mode is that of radiantly-emitted light 
without reflection. The reflector has an aperture which serves as a 
cut-off for this direct radiant illumination, and this light is emitted 
generally as a cone, and provides general low-level illumination, even 
outside of a central area yet to be described. The intensity of this 
direct radiated light decreases very rapidly at distance from the bulb 
because it is not collimated or controlled as is the reflected light. 
While substantial, the "conical volume" of this illumination from the 
filament is considerably less than the reflectively projected light which 
is reflected by the reflector in a designed, directed, pattern. It is the 
reflected projected light which provides almost all of the useful 
illumination from the flashlight. This useful illumination is the 
combination of light from the filament which goes reversely to the 
reflector, and also light which goes forwardly and still meets the 
reflector. 
It is an object of this invention to provide a reflector which can project 
the light in either a spot beam or in a broad beam, both of which beams 
will be without substantial unilluminated areas over a substantial range 
of distances. It is a matter of great frustration with a conventional 
flashlight to find that, in the broad beam setting, the area of greatest 
interest is also that of darker or little illumination. 
There is yet another problem with the common flashlight. Conventional 
reflector design is based upon the concept of a point source of light, and 
a focal point of a reflecting surface of revolution, usually a paraboloid. 
This is good theoretical geometry, and flashlights designed this way are 
sold by the millions. The imperfections of their projected light patterns 
have been overlooked in the absence of a better alternative. 
The major problem in designing a flashlight which can produce both a spot 
beam and a broad beam is that the spot beam is best provided by a 
parabolic reflector with the light source close to the focus of the 
paraboloid. In order to broaden the beam, the light source is moved 
further away from the focus. This movement, depending upon its magnitude 
and the distance between the flashlight and the illuminated area, results 
in distortions such as unilluminated regions, usually in regions of 
greatest interest. 
Conventional reflector design generally ignores these variations, sometimes 
by changing some areas of the reflector from a smooth surface of 
revolution to ones which include small discrete flat surfaces, or to an 
"orange peel" texture. These alterations serve largely to disguise the 
shortcomings of the reflector by scattering or diffusing some of the 
light. This is done at the trade-off cost of reducing the intensity of the 
light where it is needed the most. 
Another major problem which is generally overlooked is that the filament of 
the conventional light bulb is not a point source. Instead, it is a curved 
line source, and therefore cannot be a point source anywhere. Even worse, 
not only must it inherently extend laterally from the central axis of the 
reflector, but due to variations in manufacture, no part of it at all may 
actually be on the central axis. Because the dimensions of the usual 
reflector are relatively small, even very small excursions of the filament 
from the central axis result in substantial deformations of the projected 
light pattern. In fact, in typical flashlights, a shift of only 0.1 inches 
along the axis is required to change from spot beam to broad beam, and 
even smaller ones in radial directions result in substantial distortions 
of the projected pattern. 
The conventional adjustable or fixed beam flashlight has a flashlight axis 
related to a support such as its handle. Usually there is a method to 
align both the bulb axis and the reflector axis to the flashlight axis. 
The classical solution is to provide registry surfaces to hold both the 
bulb and the reflector in line as a single adjustment so they cannot be 
moved radially or angularly from the registered position. If the 
conformation of the bulb and of the reflector relative to the registry 
surfaces are both exact, all is well. However, this is rarely the 
situation. This is because the light bulbs used in these flashlights have 
a filament, usually a coil with a finite length, some or all of which is 
certain to be disposed off of the axis of the bulb, and if it is, then it 
certainly will be off of the axis of the reflector. The result is that 
although the bulb axis and the reflector axis are aligned, the filament is 
misaligned. The registry surfaces prevent any adjustment either radially 
or angularly. As a result of the filaments being off of the reflector axis 
and of having a finite size, the conventional paraboloidal reflector 
produces a spot beam that is irregularly shaped and has dimensions 
considerably larger than the maximum diameter of the reflector. The result 
is a duller spot beam than an ideal spot beam of smaller size. In 
addition, the adjustable beam flashlight with a paraboloidal reflector 
will produce a broad beam with an illuminated ring of light surrounding an 
unilluminated center disc precisely where the flashlight is aiming and in 
the region of greatest interest. These faults and the methods to overcome 
them will be made clear by the teachings of this patent. 
It is an object of this invention to provide means to improve the 
distribution of reflectively projected light by adjustably positioning the 
filament in a uniquely contoured reflector. 
SUMMARY OF THE INVENTION 
This invention incorporates a reflector which can provide either a spot 
beam or a broad beam. In some applications it will be enabled to provide 
both selectively by axially shifting the reflector and the light source 
relative to one another. 
The reflector has a concave reflecting surface in which a light source is 
positioned. The reflecting surface is a modified paraboloid, modified from 
a reference paraboloid with respect to the same focus. When a spot beam is 
to be projected, the light source is placed at the focus. When a broad 
beam is to be projected, the light source is shifted axially from the 
focus, preferably but not necessarily toward the larger end of the 
paraboloid. 
The paraboloid is modified so as gradually to shift the rays which form the 
inner boundary of the broad beam so as to spread across the central axis 
of the reflector at a desired range of projection, thereby to fill in a 
central region of the projected pattern which otherwise would not be 
illuminated. Preferably, but not necessarily, at least some of these rays 
are parallel to the central axis, so as to remove the restriction on 
range. 
According to a preferred but optional feature of the invention, means is 
provided to align the reflector and a specific light bulb relative to one 
another, so that at least a portion of the filament is disposed on the 
central axis, preferably its central part. 
The above and other features of this invention will be fully understood 
from the following detailed description and the accompanying drawings, in 
which:

DETAILED DESCRIPTION OF THE INVENTION 
In considering this flashlight, it should be kept in mind that its ultimate 
objective is to produce a spot beam or a broad beam, both of which have 
substantial illumination across their projected patterns over a wide range 
of distances from the reflector to the target surface. It is suitable for 
use only to provide a good spot beam, and for use only to provide a broad 
beam. It can also be used to provide both such beams selectively. 
Before the description of this unique reflector can be understood, it will 
be necessary to develop several geometric relations for the reflectively 
projected light rays that are emitted by an incandescent light bulb which 
has a finite size filament and that may or may not be on the axis of the 
bulb, and which may or may not be located axially at the focal point of 
the reflector. 
As a starting point, consider a light source that is concentrated at a 
single point as illustrated in FIG. 1. FIG. 1 is a cross-section through 
the axis of a reflector 1 showing a two dimensional planar parabola 2 in 
place of the paraboloid that is actually used for a flashlight reflector. 
The conventional reflector is a paraboloid that is formed by the rotation 
of the parabola 2 about the axis 3. The parabola is defined by the 
relations R.sup.2 =2px where R is the radial distance perpendicular from 
the axis 3 to the surface 2, p is a constant that determines the size of 
the parabola, and x is the distance measured along the axis 3 from the 
apex 9 of the parabola 2. 
The light source will be treated first as a point source in order to 
simplify the teachings of this patent. In later discussions, a filament of 
finite size, positioned both on and off of the bulb axis will be treated. 
As is illustrated in FIG. 1, all of the rays that originate from the bulb 
which is shown as a point source 4, when they meet the reflector, will be 
reflected spectrally from the surface 2 at an angle "a" that equals the 
angle of incidence "b". The angles "a" and "b" are measured from the 
tangent 5 at any point on the surface 2. The location of the light source 
4 along the axis 3 is given as x.sub.b. The location of the focus of the 
parabola is given as x.sub.f. The location of the light source is 
indicated by "0" when at the focus and by "X" when located at any other 
point on the axis. 
FIG. 1 illustrates, as an example, the tangent 5 located at the maximum 
diameter of the reflector and the light bulb 4 as a point source of light 
"0" that is consequently located at the focus where x.sub.b =x.sub.f. The 
direction of the light rays 6 from the source 4 that are directed towards 
the maximum diameter of the reflector will be referred to as the forward 
direction. The direction of the light rays 7 that are emitted from the 
light source 4 towards the minimum diameter of the reflector will be 
referred to as the backward direction. This portion of the discussion 
treats only light which is reflectively projected, both forwardly and 
rearwardly. Radiantly emitted light which passes through the aperture 
without reflection, is treated separately since it produces a negligible 
amount of the useful illumination. 
As is illustrated in FIG. 1, if the light source 4 is a point and is 
located at the focus x.sub.f of the paraboloid, all of the reflected rays 
8 will emerge parallel to the axis 3. The fact that the light rays are 
reflected parallel to the axis is well known when the light source is at 
the focus (x.sub.b =x.sub.f) of the paraboloid. This result can be seen by 
considering the geometry of the system illustrated in FIG. 1 and the fact 
that the angle of incidence "b" is equal to the angle of reflection "a". 
The detailed geometry to indicate the direction of the reflected light 
rays will be developed later in this discussion. This paraboloidal 
reflector with a point source at the focus would produce the "ideal" spot 
beam with all of the reflectively projected rays being parallel to the 
axis 3 and forming a beam whose maximum size is equal to the maximum 
diameter of the reflector. 
There is an area 10 in FIG. 1 at the apex of the paraboloid that has no 
reflective surface. This is the opening that accommodates the light bulb. 
As a result, the spot beam that is formed from a point source that is 
located at the focus of the paraboloid will have an unilluminated center. 
The diameter of the unilluminated disc is approximately one-third of the 
maximum diameter of the beam for a typical flashlight. Although the light 
radiated in a forward direction from the bulb that does not strike the 
reflector will cover the center disc, it is spreading spherically and 
consequently has a very low intensity a short distance from the 
flashlight. In order to illuminate the center of the beam, the point 
source is sometimes moved slightly from the focus to cause the reflected 
light rays to cross the axis. The effect will be clear from the following 
teachings. 
FIG. 2 illustrates the point source 4 displaced from the focus "O" of the 
parabola to a location "x" (x being greater than x.sub.f) along the axis 3 
in a forward direction in order to form a broad beam. For this condition, 
the light rays 6 and 7 will be reflected from the surface 2 at angles so 
that the projected rays 21 cross over the axis 3 and at some distance from 
the reflector spread out and form the broad beam. 
It will be helpful in these teachings to develop at this time the geometric 
relations for the angles of the reflected light rays with a point source 
on the axis of the reflector. 
A general relation for the angle "d" in FIG. 2 when the point source is at 
any arbitrary location x on the axis 3 will be developed to aid in 
understanding this invention. Consider a point source of light 4 located 
on the axis 3 of the reflector as illustrated in FIG. 3. The light rays 7 
that are emitted in a backward direction will reflect from the surface 2 
at an angle relative to the axis 3 that equals (c+2e-180). This relation 
follows since the angle of incidence "b" equals the angle of reflection 
"a" and the following relations as seen from FIG. 3: 
EQU a=b (1) 
EQU d=a-e (2) 
EQU b+c+e=180.degree. (3) 
It follows from equations (1), (2) and (3) that: 
EQU d=2e+c-180.degree. (4) 
where "d" is positive, measured in the counter clockwise direction. 
For light rays 6 that are emitted in the forward direction, the angle "d" 
that the reflectively projected rays form to the axis 3 is seen with the 
aid of FIG. 4. 
EQU a=b (5) 
EQU b=c-e (6) 
EQU a=e+d (7) 
It follows from equations (5), (6) and (7) that: 
EQU d=2e-c (8) 
The angle "d" is positive when measured in the counter clockwise direction 
from a parallel to the reflector axis. The angle "c" is the angle whose 
tangent equals (R/L) where L is equal to the difference between the values 
of x at the location of the point source "x.sub.b " and the value of x at 
the location that the light ray reaches the parabolic surface 2 
(L=X-x.sub.b). The angle "e" is the slope of the parabola at any point 
relative to the axis 3. The value of the "e" is determined by the equation 
of the parabola, R.sup.2 =2px and thus is the angle whose tangent is equal 
to dR/dx=p/R. It is seen that the angle that the forwardly reflected 
emitted rays form to the axis 3 are then defined as: 
##EQU1## 
The angle that the backwardly emitted light rays form with the axis 3 are 
given as 
##EQU2## 
For the special case where the point light source is at the focus of the 
parabola (FIG. 1), the value of x.sub.b is equal to the location of the 
focus x.sub.f (i.e. x.sub.b =x.sub.f =p/2). For this case it is seen that 
d=0 degrees for any value of R and that the light rays are reflected 
parallel to the axis 3 and form the "ideal" spot beam whose diameter is 
the same size as the maximum diameter of the reflector but has an 
unilluminated center disc the size of the opening 10 to accommodate the 
bulb. 
For the case where the point light source is located at any point on the 
axis between the focus and the maximum diameter of the parabola 2 the 
reflectively projected light rays cross over the axis 3 to form a broad 
beam. The magnitude of these cross over angles will be given later in this 
discussion with a numerical example for a typical adjustable (selectible) 
beam flashlight. 
FIG. 5 illustrates how, when the point source is axially displaced from the 
focus, the light rays that are emitted from a point source are reflected 
so that they cross over the axis 3 of the reflector 1 to produce a ring of 
light 51. It should be noted that the entire center region 52 is not 
illuminated except at a region 52a which is located between cross-over 
points 52b and 52c, both of which are usually so close to the reflector as 
to provide a very narrow beam. The result is that the area of most 
interest to which the flashlight is pointing when a broad beam is desired 
is not illuminated. A broad beam of this type is generally formed from a 
conventional flashlight and is highly undesirable for reasons which will 
be appreciated from a study of FIG. 5. 
It will be shown later in this discussion by a numerical example that the 
rays 53 of light which illuminate the maximum diameter of the illuminated 
ring 51 are reflected from the minimum diameter of the reflector. The rays 
54 of light that illuminate the minimum diameter of the illuminated ring 
51 are reflected from the maximum diameter of the reflector. This is an 
important result to understand so that later discussions can teach how 
this invention can produce a broad beam with no unilluminated regions 
without also causing excessive enlargement of the size of the spot beam, 
and also without decreasing the brightness of the projected spot beam 
compared to the "ideal" spot beam, all over a substantial range of 
distances to the target. 
Up to this time, the discussion has been limited to a theoretical condition 
where the light source is a point that is located precisely on the axis of 
the reflector. The light source for the conventional flashlight is not a 
point source, because it is an incandescent bulb that has a filament of 
finite size. An additional factor that contributes to the degradation of 
the spot beam is the manufacturing tolerances for the light bulb. These 
tolerances cause the filament to be located off of the axis of the bulb 
and, since the bulb is aligned to the reflector, the center of the 
filament will not be aligned on the axis of the reflector, and perhaps 
none of it is. Since the filament has a finite size and often all of it is 
located off of the axis of the reflector, it is impossible to obtain the 
"ideal" concentrated spot beam of the size of the reflector maximum 
diameter with the conventional flashlight. The magnitude of the 
degradation from an ideal spot beam with a point source compared to the 
actual spot beam with a finite size filament, and with an off-axis 
filament will now be presented. 
First, a discussion of the effect of a finite size filament whose axis lies 
entirely in a plane with the reflector axis will be presented. This is the 
case for a perfectly aligned filament with its center on the reflector 
axis. FIG. 6 is a cross-section along the axis of the filament of a 
typical flashlight bulb having a filament 61 that is perfectly aligned 
with the reflector axis and extends a length "r" from the axis 3 and a 
distance "1" from the forwardmost part of the filament. The filament is 
enlarged in comparison to the reflector surface 2 in order to make the 
teachings of this patent easier to understand. The center of the filament 
is located at the focus of the reflector (x.sub.b =x.sub.f) and the two 
ends lie equal distances from the center. Since the center of the filament 
is at the focus, the light rays emitted from the center will be reflected 
from the surface 2 in a direction that is parallel to the reflector axis. 
In FIG. 6 consider the light rays that are emitted by one extreme end of 
the filament in a plane that contains the axes of both the filament 61 and 
the reflector 2. Light ray 62 is emitted in a forwardly direction from the 
end 61a of the filament 61 to the maximum diameter of the parabola 2 (at 
its exit aperture). The reflected ray 63 is at an angle "d" from the axis. 
The light rays that are emitted in the plane containing the filament axis 
and the reflector axis 3 form an angle "d" relative to the axis 3 that has 
the same relation as equation (8) except that in this case the angle "d" 
is defined as the angle whose tangent equals (R-r)/L rather than (R/L). 
Thus the angle "d" is given by: 
##EQU3## 
where x.sub.b is the location of the center of the filament on the 
reflector axis, r is the distance from the center of the filament radially 
to the end of the filament, 1 is the distance from the center of the 
filament to the end point measured parallel to the axis 3, and x is any 
axial position of the reflector surface 2. 
In a similar fashion, the backwardly emitted rays 64 will be reflected at 
an angle "e" with the axis of the reflector equal to: 
##EQU4## 
It has been shown that for the spot beam setting, the center of the 
filament is positioned at the focus of the paraboloid and all light rays 
that are emitted from the center point will be reflectively projected in a 
direction parallel to the reflector axis. It has been shown also that the 
light rays that are emitted from the end of the filament in a plane that 
contains both the reflector axis and filament axis will be reflected to 
form an angle "d" specified by equations (12) and (13). 
It will be helpful in determining the angles of the light rays that are 
reflected in planes that do not contain both the reflector and filament 
axis to derive the relationships in a simpler fashion for the finite size 
filament. Refer to FIG. 7 where the angles of the rays emitted from the 
end of the filament are identified by lower case letters and those from 
the center of the filament by capital letters. A simplified relation can 
be derived when it is realized that the light rays emitted from the center 
of the filament will reach the reflector surface 2 at an angle "B" that is 
different from the angle b for the rays emitted from the end of the 
filament and that the difference equals the angle "g". 
It is seen that the angle of the reflected ray 73 that originated from the 
center of the filament is "g" degrees more than the reflected ray 74 from 
the end of the filament. If the center of the filament is placed at the 
paraboloid focus, the angle "D" is zero and the reflected ray 74 has an 
angle equal to "g" measured parallel to the reflector axis. 
It can be seen from FIG. 7 and equations (14) and (15) that the difference 
between the direction of the reflected rays 73 that were emitted from the 
center of the filament and reflected rays 74 from the end of the filament 
is equal to the difference between the angles C and c. 
EQU g=f-F (14) 
EQU C+F=c+f (15) 
EQU g=C-c (16) 
When the center of the filament is at the focus of the reflector D=0, and 
the rays 74 are reflected at angle "d" relative to the axis 3. 
##EQU5## 
Similarly for the rays emitted in a backwardly direction, use of equation 
(17) with the help of FIG. 8 will provide the simplified relation for the 
angle of the reflected rays: 
##EQU6## 
When the center of the filament is at the focus of the reflector D=O and 
the rays 81 are reflected parallel to the axis 3 and the rays 82 are 
reflected at an angle relative to the axis 3 of: 
##EQU7## 
Up to this point in the discussion, only the light rays that are in the 
plane which includes both the filament axis and the reflector axis have 
been considered. In order to determine the size of the spot beam, however, 
it will be necessary to consider the light rays that are reflected in 
other planes. FIG. 9 illustrates the plane 91 that contains the reflector 
axis 3 and the filament 61 as well as the plane 92 that is perpendicular 
to the filament axis and contains the reflector axis, but not the filament 
axis. 
If the center of the filament 61 is on the axis of the paraboloid, all of 
the rays emitted from that location will be reflected in planes that 
contain the reflector axis. The light that is emitted from other points on 
the filament will not be reflected in planes that contain the reflector 
axis except for the one plane 91 that contains both the filament axis and 
the reflector axis. This condition and others will be made clear by 
considering FIG. 9 which illustrates a cross-section of the paraboloidal 
reflector cut through the axes of the reflector and the filament (plane 
91) and cut through a plane 92 which is perpendicular to plane 91. 
It was shown by equations (16) and (17) that the difference between the 
angles of two rays reflected from any point on the reflector is equal to 
the difference between the angles that those rays make with the axis of 
the reflector from their points of emittance. For the case where the 
center of the filament is on the axis of the reflector at the location of 
the focus, the light rays 94 that are reflected from that point will 
emerge at an angle that is parallel to the axis 3. The light rays that are 
emitted from the end of the filament in plane 91 in a backward direction 
can be determined from equation (20). The light rays 93 that are emitted 
from the end of the filament to a point on the reflector 94 that lies in 
plane 92, can be seen from FIG. 9 to be at the angle: 
##EQU8## 
It is interesting to notice that the reflected ray 93 is not in any plane 
that contains the reflector axis. 
In a similar way, the rays that are reflectively projected in a forwardly 
direction in plane 92 can be evaluated with the aid of FIG. 10. Light ray 
101 originated from the center of the filament which is at the focus of 
the paraboloid and consequently reflects in a direction that is parallel 
to the axis 3. Light ray 102 was emitted from the end of the filament and 
consequently has an angle relative to the axis as specified by equation 
(22). Reflected ray 102 is not in any plane that contains the reflector 
axis. 
##EQU9## 
The teachings of this patent will become clearer by a numerical example. 
Consider a typical D-cell size flashlight with a typical commercial light 
bulb. The typical reflector has a maximum radius that is equal to 0.93 
inch, a minimum radius of 0.30 inch in order to accommodate the light 
bulb, and a length of the paraboloidal reflector measured from the apex of 
1.25 inch. The surface of revolution can be represented as a parabola 
having the formula R.sup.2 =2px where p=0.346 and having a focus located 
at x.sub.f p/2=0.173 inch. The equation of the parabola that fits these 
conditions is R.sup.2 =0.692x. The typical light bulb has a filament that 
is 0.050 inch long (r=0.025) and whose ends are 0.010 inch from the center 
measured parallel to the reflector axis (1=0.010). For this light bulb 
that is assumed to be perfectly aligned with the axis of the reflector, 
the light rays in the plane of the filament and the reflector axes that 
were reflected from the minimum diameter will form a spot beam of a size 
determined by the angle: 
##EQU10## 
The light rays in the plane perpendicular to the axis of the filament will 
diverge at a larger angle: 
##EQU11## 
The rays in any other plane between planes 91 and 92 will diverge at 
smaller angles and need not be considered in determining the size of the 
spot beam. 
If the light source was a point located at the focus of the paraboloid, the 
spot beam would have an unilluminated center disc of 0.30 inch radius. 
However, because of the finite length of the filament, the spot beam 
illustrated in FIG. 11 is deformed to produce a non-uniform pattern 110 of 
illumination that covers the center disc. The spot beam that is formed by 
this reflector and filament will have the size and shape shown in FIG. 11. 
At a distance of 20 feet, the spot beam will be: 
##EQU12## 
It is soon that the "typical" flashlight with the "typical" filament will 
produce a spot beam at a 20 foot distance that is over 175 times the size 
of the "ideal" spot beam and consequently will be 1/175 times as bright. 
It should be noted that the light rays that form the outer contour of the 
spot beam are reflected from the minimum diameter of the reflector. Since 
the maximum diameter surface of the reflector has rays that diverge only 
approximately one degree at the spot beam setting while the minimum 
diameter reflects rays at far greater angles, the slope of the maximum 
diameter surface could be increased without degrading the spot beam. This 
conclusion will be employed in designing the new unique reflector contour 
according to this invention. 
The other cause of the spread from the ideal spot beam is the result of 
manufacturing tolerances that result in placing the filament off of the 
axis of the bulb, or unsymmetrical to the axis. The spread because of a 
displacement off of the axis can be calculated from the same equations 
used for the filament of finite size. If the center of the filament is 
0.050 inch off of the axis, the rays from that point in the plane of the 
filament will diverge at an angle of 1.61 degrees as determined by 
equation (13). The rays in the plane perpendicular to the axis of the 
filament will diverge at an angle of 9.37 degrees as determined by 
equation (21). In addition to these angles, the rays emitted from the ends 
of the filament will be reflected at even greater angles. It is clear that 
it would be highly desirable to eliminate this off of axis fault and 
consequently reduce the size of the spot beam and increase the intensity 
of illumination. 
It has been shown that a finite size filament will produce a larger and 
consequently duller spot beam than the ideal spot beam from a point 
source. It has also been shown that the conventional flashlight does not 
correct for bulbs having a filament that is off of the axis and thus 
produces a larger and correspondingly duller spot beam than the ideal spot 
beam. It has also been shown that a paraboloidal reflector, even with a 
point light source, will produce a broad beam with an undesirable 
unilluminated center region. The spot beam from a point source at the 
focus also produces an unilluminated center disc, but it can be corrected 
by moving the source along the axis slightly away from the focus and 
consequently not degrade the spot beam very much. 
It is possible at this point to describe the unique reflector that will 
overcome all of the faults of the typical available reflectors. 
First, a description will be presented showing how the unilluminated center 
region in the broad beam can be corrected to result in a uniformly 
illuminated optimum broad beam without degrading the spot beam. 
Equations (13) and (21) specify the angles that define the outline of the 
spot beam by the light rays that are reflectively projected from the 
minimum diameter of the reflector. Equations (12) and (22) specify the 
size of the spot beam by light rays that are reflected from the maximum 
diameter of the reflector. It was shown that some of the rays reflected 
from the minimum diameter form the outer region of the spot beam and that 
those that are reflected from the maximum diameter of the reflector form 
the center region when the point source is displaced from the focus. It 
was shown by equations (21) and (22) that the rays from the end of the 
filament that are reflected by the minimum diameter form a portion of the 
spot beam that is farther from the center than the rays that are reflected 
from the maximum diameter. The fact that the maximum diameter surface of 
the reflector can be modified without affecting the size of the spot beam 
is the genesis of this invention. 
A numerical example will aid in the teachings of this specification. 
Consider the same conventional flashlight described previously. It was 
shown, and illustrated in FIG. 5, that the unilluminated center of the 
broad beam from a typical D-cell size flashlight is formed because the 
light rays that are reflected from the maximum diameter surface of the 
reflector will diverge from the parallel to the axis. The size of the 
unilluminated disc will be determined by the angles of the light rays that 
are emitted from the point of the filament that is located on the axis of 
the reflector and are reflected from the surface at the maximum diameter 
of the reflector. Equation (9) allows the angle of these rays to be 
calculated when the bulb is placed 0.100 inch forward of the focus 
(x.sub.b =X.sub.f +0.100=0.273): 
##EQU13## 
If the angle of the maximum diameter surface were increased by an amount 
equal to 2.78/2 degrees, the light rays would be reflected at an angle 
parallel to the reflector axis and would cause the rays to illuminate the 
center of the broad beam. It will now be shown based on the teachings of 
this patent that changing the slope of the maximum diameter surface will 
not result in an undesirable increase in the size of the spot beam, but 
instead will produce a desirable more pleasant uniform intensity spot 
beam. 
It has been shown that the spot beam formed from the light rays that are 
reflected from the minimum diameter of the reflector will determine the 
size of the spot beam. For the typical D-cell size flashlight, the light 
rays that are emitted in the plane of the filament and the reflector axes 
diverge by 1.34 degrees (eq. 24) and those emitted in the plane 
perpendicular to the filament axis diverge by 5.08 degrees (eq. 25). These 
angles determine the size of the spot beam since the light rays that are 
emitted in any plane are reflected from the maximum diameter surface at 
much smaller angles. 
Equation (12) determines that the spot beam that is formed by the rays 
which are reflected from the maximum diameter surface that were emitted in 
the plane of the filament and reflector axis have the value 
##EQU14## 
Equation 22 determines that the light rays which are reflected from the 
maximum diameter surface that were emitted in the plane perpendicular to 
the filament axis would form a spot beam determined by: 
##EQU15## 
It is seen that the size of the spot beam which is formed from rays that 
are reflected from the maximum diameter surface is much smaller than the 
rays that are reflected from the minimum diameter (i.e. 1.030 degrees or 
1.084 degrees compared to 1.589 degrees and 5.047 degrees). The reflected 
rays of all surfaces between the minimum and maximum diameters will 
diverge at angles between those from the extreme diameters. 
It should be realized that, since the size of the spot beam is determined 
by the minimum diameter surface of the reflector, the slope of the maximum 
diameter surface can be increased somewhat without affecting the spot 
beam. In the example, if the slope of the maximum diameter surface were 
increased from p/R=0.346/0.93=0.372 (i.e. 20.41 degrees) to 0.400 (i.e. 
21.80 degrees) the new surface would direct the light in a 
counter-clockwise direction by 2(21.80-20.41)=2.78 degrees and, 
consequently, illuminate the center of the broad beam. This change in the 
slope at the maximum diameter of the reflector to redirect the reflected 
ray by 2.78 degrees when the bulb is at the broad beam setting, will also 
cause a redirection of 2.78 degrees when the bulb is at the spot beam 
setting. Since the spot beam is formed by light rays from this minimum 
diameter surface having an angle 1.589 degrees in the plane of the 
filament and 5.047 degrees for rays in the perpendicular plane, the light 
rays from the maximum diameter surface that are reflected at 2.78 degrees 
would not produce a larger spot beam. In fact, the slight spreading of the 
rays from the maximum diameter would form a more uniform intensity spot 
beam and thus a more pleasant appearing beam. 
It has been shown that the slope of the maximum diameter surface of the 
reflector could be increased to illuminate the center of the broad beam 
without degrading the spot beam. It remains only to show how the minimum 
surface can be joined to the maximum surface in order to produce the 
optimum spot beam and broad beam. 
One of the simplest configurations is described in Ellion U.S. Pat. No. 
4,984,140 as a frusto-conical surface that is a tangent continuation of 
the paraboloid and having a half-angle equal to the desired slope that 
will illuminate the center of the broad beam. While the configuration of 
U.S. Pat. No. 4,984,140 is very functional, the inventor therein and also 
in this instant application has concluded that a superior configuration is 
possible that will produce an improved spot beam and a more uniform and 
pleasant broad beam having no unilluminated center. 
FIG. 12 illustrates a conventional paraboloidal reflector 120. Shown in 
phantom is the unique reflector 121 according to this invention. The new 
reflector can be described as having a slope which at least equals that of 
the conventional paraboloidal reflector but which varies from it 
monotonically to the maximum diameter where it has a slope such that the 
light rays incident on it from the bulb are reflected in a parallel 
direction when at the broad beam setting. If the desired increase in the 
slope of the maximum diameter surface is given as "S" and since the slope 
of the conventional parabola is dR/dx=p/R=(p/2x).sup.1/2, one version of 
the desired reflector can be written as: 
##EQU16## 
It is seen that the slope of the reflector will vary from that of a 
conventional paraboloid in a linear fashion to the desired slope at the 
surface of maximum diameter. Equation 26 can be integrated to give the 
equation of the desired linearly modified parabola. 
##EQU17## 
The general equation for the desired reflector will have the form: 
EQU R=AX.sup.1/2 +BX+CX.sup.2 +D (28) 
To ensure that the reflector is sufficiently long so that the rays which 
are reflected from the maximum diameter will illuminate the center of the 
broad beam, it is necessary to determine the maximum radius or the value 
of x.sub.max. FIG. 13 illustrates the conventional parabolic reflector 132 
with light ray 131 emitted from the center of the filament on the axis of 
the reflector and reflecting from the maximum diameter of the reflector. 
For the numerical case in the example, the reflected ray will have an 
angle of 2.78 degrees from the axis. It will be the intersection of this 
ray line with the new modified parabola 133 that will locate the maximum 
diameter of the modified parabola. The equation of the light ray is given 
by: 
##EQU18## 
where the capital letters refer to the modified parabola and the lower 
case letters refer to the conventional parabola. For the typical D-cell 
size flashlight, equation 30 becomes: 
EQU R.sub.max =0.9519X.sub.max -0.2599 (31) 
The equation of the modified paraboloid in a convenient form can be 
obtained by integrating equation (26) from R.sub.min to R.sub.max to give: 
##EQU19## 
The equations (29) and (31) when solved simultaneously yield the value of 
the maximum radius for the unique linearly modified parabola. In this 
case, a simple trial and error solution yields the values R.sub.max =0.956 
and x.sub.max =1.278. It is seen that the linearly modified parabola is 
only slightly longer and has only a slightly greater diameter than the 
conventional reflector. 
##EQU20## 
A second integration for the desired increase in slope, S, is necessary 
since the length of the modified reflector is increased to 1.278 from 1.25 
inches. Consequently, the desired increase in the ray angle (2.70 degrees) 
should be based on the conventional paraboloid length of 1.278. The slope 
at the maximum diameter of the conventional paraboloid is 
p/R=P/(2px).sup.1/2 =0.368. Since we desire a surface slope of 21.8 
degrees, the correct value of S is tan 21.8-0.368=0.032. The equation of 
the modified paraboloid for the typical flashlight in the previous example 
becomes 
EQU R=0.832x.sup.1/2 -0.00378x+0.1396x.sup.2 -0.000216 (33) 
In practice the reflector would be made slightly longer so that the light 
rays reflected from the extended section would further illuminate the 
center of the broad beam to produce a more pleasant effect. 
There remains to demonstrate another unique feature of this reflector to 
correct for the location of a filament which is off of the axis of the 
bulb and, since the bulb structure and the reflector axis are generally 
aligned, will also be off of the reflector axis. 
FIG. 14 illustrates in cross-section a filament 141 that is oriented 
angularly in the correct manner to the reflector axis 143 but whose axis 
144 through the center of and perpendicular to the filament is off of the 
axis of a reflector. FIG. 14 also illustrates in cross-section reflector 
146 with holes 142 that are larger than the diameter of the attachment 
bolts 143 so that the reflector can be positioned radially from the 
flashlight axis 145 as to position the filament axis 144 coincident to the 
reflector axis 145. When the reflector and the filament are properly 
aligned, the bolts are tightened in order to maintain that condition. Each 
time a new bulb is installed, the reflector should be repositioned. 
FIG. 15 illustrates in cross-section a filament 153 with axis 152 that is 
misoriented relative to the axis 154 of a reflector 155. In this case 
reflector 155 has a set of other adjustable screws 151 that can correctly 
align the axis of the reflector 154 with the filament 152. FIG. 15 
illustrates one technique for this alignment. Adjustment of screw 151 into 
the reflector and screw 151a out of the reflector will cause a rotation 
that will align the reflector and filament. 
In adjusting the off axis filament or the misoriented filament, the 
reflector is moved until the flashlight produces the desired optimum spot 
beam. Either radial or angular adjustment can be provided, or both if 
preferred. 
Selection of spot beam or of broad beam can be made by axially shifting 
either the bulb or the reflector, or both. Generally it will be preferred 
to move the reflector, because the position of the bulb will be related to 
the batteries. Mechanical means for shifting the reflection are shown in 
said U.S. Pat. No. 4,984,140, which is incorporated herein by reference 
for such a disclosure. 
FIG. 16a illustrates the shape of a spot beam from a conventional 
paraboloidal reflector with a light source whose filament is off of the 
reflector axis. The various areas of illumination are shown in relative 
size for a D-cell flashlight whose filament is 0.050 inches long and is 
displaced from the axis by 0.050 inches in a direction perpendicular to 
the filament axis. The filament axis is in a vertical orientation for 
these figures. The "+" is the point at which the flashlight is pointing. 
Region 161 has the greatest intensity; region 162 is less bright; and 
region 163 is the dullest. 
FIG. 16b illustrates the effect of aligning the filament according to this 
invention so that the center of the filament is on the axis of the 
reflector and at the focus. 
FIG. 16c illustrates the spot beam with the filament aligned and its center 
on the axis of the modified paraboloidal reflector according to this 
invention. The spot beam is more uniform and of more pleasing shape. 
FIGS. 17a, 17b, and 17c show the same conditions as in FIGS. 16a, 16b, and 
16c for the case where the lamp is displaced from the focus to form a 
broad beam. FIG. 17a is the conventional reflector with an outer 
illuminated rim 172 and the unilluminated spot 171 which is slightly 
displaced from the point at which the flashlight is pointing. 
FIG. 17b has little effect on the broad beam other than moving the 
unilluminated center closer to the point at which the flashlight is 
pointing. 
FIG. 17 illustrated the broad beam from the modified paraboloidal reflector 
according to this invention. It shows a fully illuminated broad beam. If 
the reflector were made slightly longer than the minimum required length, 
the center of the broad beam would have a brighter spot. 
With the foregoing theoretical disclosure and the disclosed examples in 
mind, FIGS. 18-19 are presented to summarize the shortcomings of the prior 
art and the means by which this invention overcomes them. Again, the 
objective is to produce either a spot beam, or a broad beam, or 
selectively either one, in which the same reflector can produce either or 
both. In so doing, the spot beam will have at least the quality produced 
by known flashlights over a substantial range. Also the same reflector can 
produce a broad beam of substantially improved quality over a large range, 
compared with known flashlights. By quality is meant a projected pattern 
without dark spots or rings with reasonably uniform intensity over the 
illuminated area. In addition, when alignment means is provided between 
the lamp and the reflector, the projected pattern can be adjusted to be 
closer to circularity than is attainable with known flashlights, although 
in view of the linearity of the filament, it will tend toward an ellipse. 
FIG. 18 shows a true parabolic reflector 170 reflecting light from a point 
source 171 at the focus 172 of the paraboloid. This beam is cylindrical, 
with a circular, cylindrical illuminated band 173, and a dark, 
unilluminated core 174. Since the light source is not a point, but rather 
is of finite length, the spot beam becomes fully illuminated but of larger 
and deformed shape than the ideal circular beam, the size of the maximum 
diameter of the reflector. The reflector according to this invention 
modifies this paraboloid so as to reflect light from the enlarged end into 
the dark region. The resulting beam will be larger than the theoretical 
spot beam, but will not have a central unilluminated area. As a matter of 
quality of projected spot beam, this quality is improved by its lack of a 
central dark spot, and the enlargement of the beam will scarcely be 
noticeable over the full intended range of distances. 
FIG. 17 shows more graphically the same true parabolic reflector 170 with 
the point source 171 displaced from the focus 172. This is to generate a 
broad beam. The effect, as also shown in FIG. 5, is to generate an 
illuminated ring 175. A central circular dark region 176 is developed 
except between points 177 and 178 along the projection axis. Both of these 
points are too close to the flashlight to be of interest in the projection 
of a broad beam. 
FIGS. 18 and 19 illustrate the serious shortcomings of the parabolic 
reflector, actually for either a spot beam or for a broad beam. 
Now compare FIG. 20. Again it should be noticed that the inside boundary of 
the projected ring, defined by ray 190 in FIG. 19 is reflected from the 
larger end of the reflector, and the outside boundary is defined by ray 
191 in FIG. 19 reflected from the smaller end. 
In FIG. 20, the included angle between the tangents to the reflector and 
the central axis have been gradually enlarged. This "brings" ray 190 
toward and past the central axis, thereby spreading some of the 
illumination into what had been a central dark region. Gradually 
increasing this angle will gradually spread the illumination. As shown, 
ray 190 is parallel to the central axis, and regardless of the range there 
will never be a dark central region. The central region will in fact be 
brighter than a surrounding ring, but the pattern will be entirely 
illuminated, and will be brightest at the center, which is generally of 
greater interest. 
FIG. 20 shows the preferred embodiment, in which ray 190 is parallel to the 
central axis. Then at any range there cannot be a dark central region. It 
is still within the scope of this invention to have ray 190 cross the axis 
at some significant distance beyond the intended range. The objective is 
to have rays 190, if not parallel to the axis, intersect it at a distance 
beyond the intended range. 
The criteria for modifying a true paraboloid in accordance with this 
invention are shown in FIGS. 21 and 22. A point source 200 of light is 
shown displaced from the focus 201 of the toward its larger end, which 
will generate the broad beam. A narrow region of the true paraboloid 
closely surrounding the aperture which receives the bulb is preferably 
maintained. This region contributes significantly to the illumination of a 
central portion of the projected spotbeam, although not right on the 
center. 
Axially beyond that, the diameter of the reflector increases gradually, and 
the angle of its tangent relative to the central angle increases. This is 
for the purpose of spreading the broad beam light toward and past the 
central axis. The theory is demonstrated in FIGS. 21 and 22. 
In FIG. 21, a reflecting tangent surface 215 is shown receiving a ray 212 
and reflecting it as ray 216. Surface 215 will be treated as the true 
parabolic surface. Now assume that a new surface 211 is formed, with its 
tangent making an angle "a" with surface 215. This is the surface of the 
invention. The same ray 212 will be reflected as ray 213. The angle 
between them is "2a". 
The effect is to tilt the reflected ray towards the central axis, and the 
gross effect of doing this continuously (or incrementally) along the 
reflector from the smaller to the larger end is to achieve the result 
shown in FIG. 20. 
That this can be done is demonstrated in FIG. 22, in which axially spaced 
tangential surfaces 220, 221 are shown. Surface 220 is closer to the 
smaller end. Its reflected ray 222 will cross the central axis and 
illuminate a region farther out radially than ray 223 from surface 221. Of 
course, the tangent point of surface 220 will be closer to the tangent to 
a paraboloid then the tangent point to surface 221. FIG. 22 is intended to 
demonstrate the theory. 
In practice, the reflector will be a modified paraboloid. The paraboloid to 
be modified is the one which will project a spot beam of the intended 
pattern diameter. 
The paraboloid is modified by gradually increasing its diameter as it 
extends from the smaller end, while also gradually increasing the angle 
between the central axis and a tangent to the reflecting surface relative 
to the conventional paraboloid. The modification is such that, when a 
point source of light is shifted axially to form the broad beam, the 
reflector will have distributed light from the outside of the beam to a 
region at least coincident with the central axis (at a desired range), and 
preferably with one boundary parallel to the central axis. 
The discussion to this point relates to forming a broad beam by moving the 
light source from the focus towards the larger diameter of the reflector. 
It is obvious that a broad beam could also be formed by moving the light 
source from the focus toward the smaller diameter. In this case the angle 
to the tangent to the modified paraboloid would be decreased as the 
diameter increases relative to the theoretical paraboloid. 
In actual practice, in order to generate the broad beam, the light source 
will be shifted away from the focus toward the larger end. This is because 
the bulb fits in an opening in the reflector, and some light is emitted 
backwardly to the reflector and is projected forwardly. When the lamp 
moves forwardly, there is an increased spacing between it and the smaller 
end of the reflector. Then, despite the presence of the passage in the 
reflector, substantial light is reflected. 
If the lamp is shifted toward the narrower end of the reflector, the 
advantages of this invention will still be attained, but to a lesser 
extent. This is because the lamp approaches the passage through the 
reflector, and will usually partially enter it. Considerable 
rearwardly-emitted light simply goes into the passage as a loss, and less 
light is available for distribution into the areas intended to be supplied 
by rearwardly-emitted light. Furthermore, the shape of the modified 
paraboloid, instead of enlarging from the theoretical shape, instead 
narrows. 
This does serve to illustrate the versatility of this invention in 
providing reflector shapes which are modified either by enlargement from, 
or by reduction from, a basic, theoretical true paraboloid for the 
intended purposes. 
FIGS. 24 and 25 show this situation. In FIG. 24, the movement of light 
source 250 toward the narrow end of a true parabolic reflector 251 
relative to its focus 172 shows that in this broad beam arrangement, outer 
rays 255 are formed from the narrow end, and rays 256 from the larger end. 
FIG. 25 in dotted line shows a reflector surface 260 according to the 
invention relative to reflector 260. In FIG. 25, the reflector surface is 
brought in, instead of out, continuously or incrementally. Notice ray 261, 
which is about the same as ray 255. However, ray 262 is moved inwardly. 
The rays between 261 and 262 fill in the target area. 
It is not expected that the embodiment of FIGS. 24 and 25 will be 
commercially utilized, because of their sacrifice of light. However, their 
design criteria are the same as for reflectors in which the light source 
will be moved toward the larger end of the reflector. 
The reflector described herein includes reflective regions for directing 
light as stated. It is possible to add on additional length to the 
reflector, and to utilize that additional length to direct or to diffuse 
light. Similarly, some areas which are the subject of this invention can 
be surface-modified, such as by orange-peel surfacing to provide a 
diffusion of light in some regions. This invention can accommodate such 
variations. 
FIG. 23 illustrates a true parabola in phantom line 280 and a reflector 281 
according to this invention. The true parabola has formula, R.sup.2 =2px, 
where R is the radial distance from the central axis to the reflective 
surface, x is the axial distance measured from the apex and p is chosen as 
2.402 so that the difference between the two reflectors is visible. This 
table will enable a person skilled in the art to make a suitable reflector 
according to this invention. The dimensions are in inches. 
______________________________________ 
Reflector 
Radius Surface Angle 
Station 
x Parabola Invention 
Parabola 
Invention 
______________________________________ 
a. 1.000 1.5498 1.5517 57.1694 57.2638 
b. 2.000 2.1918 2.2027 46.6199 47.9443 
c. 3.000 2.6844 2.7111 41.8222 42.4342 
d. 4.000 3.0997 3.1492 37.7726 38.7022 
e. 5.000 3.4655 3.5447 34.7265 35.9907 
f. 6.000 3.7963 3.9121 32.3224 33.9317 
______________________________________ 
The techniques for correcting for the off axis filament or the misoriented 
filament are not limited by these embodiments since persons skilled in the 
art could envision others such as moving the bulb rather than the 
reflector based on the teachings of this patent or other means of 
restraining the reflector relative to the filament after the adjustment. 
The foregoing examples have disclosed complete surfaces of revolution, and 
if maximum light intensity in a controlled beam is the objective, then 
these are the shapes which should be used. However, the flashlight will 
then always have a larger end with a diameter considerably larger than the 
handle to which the reflector and lamp are mounted. This is quite 
conventional and is generally accepted. However, should one wish to carry 
the flashlight in his pocket or lay it down, a flatter reflector is to be 
preferred. This will, of course, reduce the area having the shape 
according to this invention but will produce either a spot beam or a broad 
beam of lesser intensity and modified shape, which is better than 
attainable with a similar modification of a true paraboloid. Further, the 
modified surfaces themselves can have reflective properties which will 
provide illumination, but not in the same controlled pattern. 
For example, in FIGS. 26 and 27, a reflector 270 according to any of the 
foregoing examples has a dimension of width in one lateral axis at its 
larger end reduced by forming two planar reflecting faces 271, 272 
extending from end edges 273, 274, respectively, to near adjacency to the 
center hole 275. It may or may not extend through the reflecting region 
immediately adjacent to the hole. These slanting faces will also reflect 
light, but not in the same controlled pattern as the remainder of the 
reflector, which still will produce beams without unilluminated regions. 
Another example is shown in FIGS. 28 and 29, wherein a reflector 280 
according to any of the foregoing examples (except that of FIGS. 26 and 
27) has a dimension of width in one lateral axis at its larger end reduced 
by a pair of planar reflecting surfaces 281, 282 that extend parallel to 
the central axis away from end edges 283, 284, respectively. In this 
embodiment, the planar surfaces remain well spaced from the center hole 
285. Again, these planar surfaces will reflect light, but not in the same 
controlled pattern as reflected by the remainder of the reflector. 
In FIGS. 26-29, the flashlight has the advantage of thin-ness for being 
carried in a pocket or purse, and cannot roll away when laid down. 
FIGS. 26-29 further indicate that the paraboloidal surface need not be a 
complete one in order to enjoy the benefits of this invention. 
Intermediate modified or omitted regions may provide advantages of their 
own, while that portion of the reflector which is at least a part of the 
modified paraboloid will provide these advantages, although delivering 
less light. Accordingly, the claims are not intended to be limited to 
reflectors which are complete modified paraboloids. 
Also, the larger end of the modified paraboloid need not also be the larger 
end of the reflector. Extensions for various purposes such as light 
cut-off, or additional concentration of light in selected regions, or even 
for protection or retention of a lens, can be added on. Similarly, the 
modified paraboloid could also include bands of different shape should 
some "tailoring" of the beam be desired. 
While this invention will find its greatest use in hand-held flashlights, 
and the specification and claims use this term, it can be scaled to any 
size, to include handle held small lamps and large searchlights. All of 
these and similar items are intended to be included in the term 
"flashlight". Also larger items will sometimes use arcs rather than 
filaments for a light source. All sources of light are to be included in 
the term "source". 
In summary, this invention provides: 
1. An improved flashlight which selectively provides a spot beam and a 
broad beam. The modified parabolic reflector produces with either a point 
source of light or an extended filament source of light a spot beam which 
is substantially more uniform across its disc as is produced by a 
conventional parabolic reflector, and a greatly improved broad beam 
without unilluminated areas. Furthermore, the range of distances in which 
these effects are provided is importantly increased. 
2. An improved flashlight which does not necessarily produce both a spot 
beam and a broad beam, but whose reflector produces either one of said 
types of beam with substantial uniformity of luminosity across its disc, 
utilizing a filament for a light source. 
3. Adjustment means for any type of flashlight that utilizes a filament for 
a light source, which can align the filament with the central axis of the 
reflector so as to reduce distortions of the beam which were caused by 
off-axis placement of the filament. 
This invention is not to be limited by the embodiments shown in the 
drawings and described in the description, which are given by way of 
example and not of limitation, but only in accordance with the scope of 
the accompanying claims.