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Патент USA US2110590

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lvlarch~ 8, 1938.
J, F, CQQK, JR
2,110,590
REFLECTING INCANDESCENT LAMP
Filed Sept. 11, 1936
. 1770621502"
by W//
7(mgk/1/W
‘I? QM.
viormjgs
Patented Mar. 8, 1938
" 2,110,590
UNITED STATES PATENT ‘ OFFICE ’
2,110,590
REFLECTING INCANDESCENT LAMP
Joseph Francis Cook, Jr., West Roxbury, Mam,
assignor to Birdseye Electric Corporation,
Dover, DeL, a corporation 01 Delaware
Application September 11, 1936, Serial No. 100,285
7 Claims. (Cl. 176-34)
This invention relates to' improvements in the
design and construction of incandescent lamps
and particularly incandescent lamps having a
part of the bulb surface coated with a re?ecting
5 material arranged to re?ect a large part of the
rays from the‘ incandescent source and concen
Fig. 4 is a sectional‘ plan view showing the loca
tion and shape of the V-shaped ?lament.
One satisfactory re?ecting medium for lamps
of my invention is metallic silver deposited upon
the inner surface of the bulb in accordance with 5
the process of Pincus Deren disclosed in applica
trate and direct them on the area of useful work.
tion Ser. No. 42,227, but the invention is in no
The particular improvements of this invention
concern the shape and curvature of that part of
10 the lamp bulb which determines the shape of the
re?ecting surface. I have discovered that im
proved results in certain ?elds may be secured by
shaping a re?ecting portion of-the bulb as a
sense limited to the employment of metallic silver
nor to locating the re?ecting medium upon the
paraboloid of revolution, expanded until its focus,
or the locus of its focal points, constitutes a
circle of appreciable diameter and employing in
the bulb an extended ?lament concentrically or
symmetrically disposed with respect to such
circle. An incandescent lamp so designed and
20 constructed is e?ective to throw a very bright
spot of light on the center of the area to be illu
minated, and a gradually diminishing amount of
inner surface of the lamp bulb. For purposes of 10
illustration, however, two lamps are shown which
are provided with an inner coating of silver form
ing re?ecting areas.
The bulb of the lamp herein shown is sym
metrical about its axis and the re?ecting surface
is therefore also symmetrical, and may be ac 5
curately described as a surface of revolution,
formed by rotating the trace l0—l2 in Fig. l, for
example, about the axis of the bulb. The trace of
this re?ecting surface, however, was not devel- 0
oped about the axis of the lamp. It bears a
de?nite relation to this axis, and can be de?ned
That is, the area
by a mathematical equation using the bulb axis
, around the spot is brightly illuminated—less
as one of the rectangular co-ordinates, according
25 brightly than the spot however-and the inten
sity in this larger area of reduced illumination
gradually fades out at the far edge of the illu
ever, it is much simpler to de?ne the curvature of '
light on the surrounding area.
minated area. ‘ Such lamps are useful in large
store windows, for example, where the central
30 exhibits require bright spots of light, and where
the rest of the window requires .a reduced inten
sity of illumination, or in lighting gasoline ?lling
stations, where much light is required near the
Q
Li
pumps and a reduced amount elsewhere in the
yard. The gradually reduced intensity of the
outer zone permits these lamps to be grouped so
that the light patterns overlap, without produc
ing unsightly rings or bands of light and shade.
These and other features of the invention will
40
be best understood and appreciated from the fo1
lowing description of preferred embodiments
thereof, selected for purposes of illustration and
shown in the accompanying drawing in which,
Fig. ‘1 is a view of the lamp shown somewhat
conventionally in cross section,
Fig. 2 is a similar view of a lamp of somewhat
' different design,
Fig. 3 is a polar diagram of the light emitted
by the lamp of Fig. 2, and
to the practice of analytical geometry. How- 25
the re?ecting surface in terms of the method by
which it was designed. The trace of the re?ect
ing surface from l@--l2 in Fig. 1, forexample,
is a portion of a true parabola; however the 30
re?ecting surface is not a paraboloid of revolu-v
tion about the axis 20-22 of the parabolaas are
the ordinary parabolic re?ectors, such as those
used in automobile headlights, for example.
Such parabolic re?ectors are designed to operate 35
with a source of light ‘thatis as nearly as possible
a point source, and which is located in the main
axis of the paraboloid of revolution and at its
focus. In the production of commercial lamps
of high wattage-from 100 watts and above—it is 40
impossible to make use of ?laments that ap
proximate a point source, since even pure tung
sten would melt under such conditions. Gen~
erally a ?ne coil of fine tungsten or other'suit
able wire is suspended in loops or in a circle of
about 1/2" in diameter to several times this size
in lamps of high wattage. If such a ?lament is
suspended at or near the focus of a true para
bolic re?ector, generated by revolving a half,
parabola about its axis, there is obtained not a 50
9,1 1o,soo
spot-light but a mottled arrangement of brilliant
and less brilliant light directly in front of the
parabolic re?ector with much "scattered and
mottled light over a considerable area.
In the lamp of my invention I desired a strong
spot of light directly in front of the re?ecting
bulb-in line with the axis of the lamp-sur
rounded by a ?eld of diminishing intensity.
However, no part of the field should be mottled
10 with light of varying intensity, and for practical
reasons a point source can not be used.
To accomplish this desired‘ result I have de
signed the outer or lower part of the re?ecting
surface of my new lamp so that it is generated
15
by revolving the parabola l0—-|2, Fig. 1, about
the axis of the mount, and therefore the axis
of the bulb itself, but while maintaining the
focus of the parabola in the circle of the ?la
ment, the axis of the parabola being maintained
20 parallel to the axis of the mount. Thus the
shape of the parabolic portion of the re?ecting
surface with respect to each point on the ?la
ment however, is limited in extent in each case
to a line lying in a plane determined by the point
in question on the ?lament and the axis of the
lamp. ‘Those areas of the bulb-and therefore
re?ecting surface-lying adjacent to this line
are approximately parabolic with respect to this
same point on the‘ ?lament and for an appreci
able re?ecting area surrounding this line
approximately focus the light from this source. 10
The rest of the re?ecting surface, located above
the plane of the ?lament re?ects light falling
on it from this same point source in a more and
more widely divergent direction, divergence in
creasing with the distance from the parabolic 15
axis, and this divergent light, from the in?nite
number of point sources which compose the cir
cular ?lament comes an important part of the
total used to illuminate the larger ?eld of gradu
ally diminishing intensity, surrounding the cen 20
tral brightly illuminated spot.
Thus it will be seen that the re?ecting sur
surface becomes a paraboloid of revolution in
which each element has been displaced outward . face, with the parabolic trace, below the plane of
the ?lament concentrates a considerable part of
ly with reference to the axis of the mount a dis
25 tance equal to the radius of the circle of the the light falling on it in a spot directly in front of 25
the lamp and in a line with the axis of the bulb
?lament. It will be seen that under these cir
cumstances the locus of the focal points of all and tends to surround this spot with a ?eld of
the displaced elements of this paraboloid of gradually diminishing intensity.
‘Added to this effect is the direct light from the
revolution lie in the circle which also contains
?lament that passes through the transmitting 30
30 the ?lament: or that the mraboloid has been ex
panded until its focal point becomes a locus of portion 28 of the bulb, which, without any re?ec
tion, fans out with constantly diminishing in
points which is a ring coinciding with the gen
eral contour of the ?lament or circumscribing tensity, on a plane surface perpendicular to the
axis of the lamp, being brightest at a point
the ?lament.
35 It will be understood that by a circular type nearest to and directly in front of the lamp, on 35
?lament I mean one which lies in a plane and the axis of the bulb, thus actually aiding in pro
which is approximately a circle or inscribed in or ' ducing, the desired effect.
The rest of the re?ecting surface within or
circumscribed about a circle so that the distance
between the wire of the ?lament and the nearest
40 point in the bulb is as uniform as possible. Such
a circumscribing circle is shown in dot and dash
lines in Fig. 4 and this may also represent the
above the plane of the ?lament requires special
consideration. One of the great dimculties in
using a true parabolic re?ecting surface in con
nection with a ?lament operating under a rela
focal circle of the parabolic re?ecting portion of
tively high wattage-400 watts for example-and
the bulb. Obviously there must be an open
45 space where the end of the circular ?lament
joins the lead-in wires, and which cannot be
closed without short circuiting the ?lament. A
V-shaped ?lament, or a ?lament of almost any
other shapeof which all parts are located in a
with the ?lament located at the focus, is the fact
that in parabolic re?ectors of reasonable design,
50 single plane perpendicular to the axis of the
mount, and disposed within the limits of the
circle which is the locus of the focal points of
the paraboloid and which are substantially uni
formlyspread over the area of this circle, will
55
produce satisfactory and substantially accurate
results with the re?ecting surfaces disclosed,
since, as has already been stated the purpose of
the lamp of this invention is to produce a bright
spot surrounded by a ?eld of gradually diminish
ing intensity of illumination rather than to pro
duce a clear-cut light spot.
The coiled ?lament has two traces I4 and I 6
where it cuts the plane of the paper, as shown in
the drawing Fig. 1. The ?lament trace I4 is
65 at the focus ofthe partial parabola l?-IZ, and
the dotted curved line It indicates the completed
half-parabola, having an axis 20-22 extending
through the focus l4 and parallel to the main
axis 24—26 of the bulb. The other trace ii of
70 the ?lament bears the same relation to the par
tial parabola on the near side of the drawing.
Thus it will be noted that for each point on the
?lament there is a true parabolic re?ecting sur
face, approximately at the focus of which lies
75 that point of the ?lament. This true parabolic
the focus is very close to the apex of the re?ector.
It is well understood that a parabola may vary
in shape depending on the mathematical for
mula for the particular curve in question. It
may be slender and narrow, or it may be broad
and ?at. A narrow, slender parabola has its
focus much closer to the apex of the parabola
than a broad ?at parabola, and the broad ?at
type are not desirable for use in re?ecting lamps
of this type for several reasons, although it
would be possible to use a broad ?at parabolic
re?ector, the focus of which was at a sufficient
distance from the apex of the paraboloid so that
an incandescent ?lament of relatively high watt
age could be used without injuring the glass.
Such broad ?at parabolas, used as the basis of a
bulb for a re?ecting incandescent lamp, would
make much too large and bulky a bulb for prac
tical purposes-much larger than the normal vol
ume requirements for a given wattage, and this
effect would be greatly exaggerated if the par
abolic surface were extended soas to hood the
?lament, and produce a cone of light, the outside
edge of which would make some desirable angle
with the axis of the cone, of say, 60 or 75°. In the 70
past, efforts to avoid this dii?culty with a par
abolic re?ecting lamp have resulted in an
arbitrary enlargement of the lamp bulb at the
apex of the parabolic cone, simply to make
greater the distance, between the bulb and the
.15.
2,110,000
?lament at the focus of the parabolic part of
3
'
ly re?ected through the opposite ?lament trace
the re?ecting surface. In the case of a‘ re
I 4. All other rays leaving trace ii on the ?lament . '
?eeting type lamp, this would result in a hit
will be re?ected by the globular part of the re
?ecting surface through points near the trace l4,
and at gradually increasing distances from II
or miss re?ection of the light falling on this
part of the re?ecting surface, and the generally
desired true spot light'would not be obtained.
as the angle of the plane containing the ray
In the lamp of the present invention the globu
lar part of the re?ecting surface, above the plane
of the ?lament is designed as a particular surface
10 with respect to the circular ?lament, and in such
under consideration makes a greater and greater
angle with the plane of the paper. On allrother
planes through the axis of the lamp. there will‘
be two traces similar to I‘ and I6, and to light
a way- that the're?ected rays from this part of . from this in?nite number of point sources on the
the re?ecting surface act as much as possible in
substantially the same wayv as those from the
parabolic part, and actually serve to reinforce the
15 e?ect of the re?ected light from the parabolic
surface. Moreover, by this design, although from
neither part of the re?ecting surface is all of the
re?ected light sent out in parallel rays, a large
circular ?lament can be applied this same dis;
cussion. Thus it will be seen, that light re?ected
from the globular part of the re?ecting surface,
is in part accurately emitted as parallel rays to 15
produce a centrally located brilliant spot of light,
and the rest of the light will be distributed over
a larger area, and at an intensity which gradually
part of the re?ectedlight is so emitted, thus form
diminishes as the distance from the central spot
of light increases. This gradually diminishing in 20
20 ing the desired spot at the center of the illumi
nated area, and all the rest of the light from the tensity feature of the larger area around the cen
?lament is emitted in a larger surrounding cone tral spot is of great importance, and it is apparent
of gradually diminishing intensity, brightest at that any abrupt ‘changes in re?ecting angles of
the center and diminishing to a low valueat the the re?ecting rays, from any point source on the
N, GI edge of the cone. As has been pointed out above,’ ?lament under consideration, as they gradually 25
this gradual diminution of intensity toward the
edge of the illuminated ?eld, without mottling,
diverge from the direction that produces parallel
is a most important characteristic of this partic
changing intensity, and a mottled illuminated
area would result.
ular lamp. The direct light from the ?lament, as
30 is well understood, meets this requirement; that
from the parabolic part of the re?ector does, also,
as has been explained above; and the re?ected
light from the globular part of the re?ecting sur
face also does, since it is used to reinforce the
re?ected light from the parabolic part ‘of the
re?ector, as is shown directly below.
The globular part of the re?ecting surface is
rays, would tend to produce an area of rapidly
' . Thus it is apparent that the re?ected light from 80
the globular re?ecting surface tends to reinforce
the effect from the parabolic portion, and that
light from these two surfaces together with the
direct light from the ?lament all contribute to
the desired ?nal result of a bright spot, centrally 35
located, surrounded by a larger area of gradually
diminishing intensity, and without any abrupt
composed partly of the re?ecting surface of the ' changes in the intensity of illumination of the
40
?oor area, for example, below the lamp.
‘The globular portion of the bulb has also the 40
bulb, indicated by the trace l0--30 in Fig. 1,
and partly of the re?ecting barrier, 32, which is
preferably a bright white metal upwardly con
important function of spacing the re?ecting coat
vex disk supported in any desired manner in the
ing sufl‘lciently from the incandescent ?lament to
location suggested in Figs. 1 and 2. The curve
of this combined re?ecting surface is continuous,
except for a small space between the bulb walls
and the re?ecting barrier 32, and the curve is a
somewhat ?attened circle and may be considered
to be an ellipse of which two points M and I6 are
the two foci, these points also being the trace of
the circular type ?lament with the plane of the
paper. It is well understood that a re?ector
shaped in the curve of an ellipse and receiving
an incident ray from a source located at one focus
will re?ect the my back to the other focus. In
(:1 LI any case the curve as shown and as used for this
symmetrical globular portion of the re?ecting sur
face is such that light striking. it in the plane
of the paper, for example, from trace l6 of ‘the
?lament will be re?ected back through trace l4
(50 and vice versa.
Thus such a ray, after being
re?ected by the globular portion of the, re?ecting
surface will appear to emerge from a point on
the ?lament directly opposite the point on the
?lament where it was originally generated. It
will thus act merely to reinforce the light coming
from the point on the ?lament directly opposite
and will either appear to emerge through the
transmitting portion of the bulb as a direct ray or
be re?ected a second time from the parabolic
part of the re?ecting surface, and, for example,
emerge as one of the parallel rays forming the
centrally located bright spot.
\
In the elliptical re?ector- of my invention, it is
apparent that only the rays leaving the ?lament
trace l6 in the planeof the paper will be accurate
permit convection currents of gas to pass across
the re?ecting surface and by the distance and
cooling effect thus provided to obviate damage to 45
the coating which might otherwise be caused by
over-heating.
‘
I do not desire to be limited in my invention
to the exact design, shape and measurements
shown in the accompanying drawing, since it is
apparent that larger sizes, for example, or lamps
giving a'larger bright spot, or a less marked dif
ference in illumination between the bright spot
and the surrounding less brilliant area, could
readily be designed and manufactured from the 55
disclosure given and without departing from the
actual invention.
The lamp shown in Fig. 2 is of slightly dif- '
ferent shape from that illustrated in Fig. 1 but
it corresponds in construction thereto. The por 60
tion generated by revolving parabolic trace 50-52
about the axis 64-66 of the bulb is provided
with an internal coating 5| of metallic silver.
The parabolic axis of this trace is shown at
60-62. The small circles 54-56 indicate the
traces with the plane of the paper of a ring
shaped ?lament which is the locus of the focal
points of all the parabolic elements of this sur
face. The portion of the bulb generated by re
volving the trace 50-10 about the axis of the 70
bulb, together with the upwardly convex re
?ecting barrier 12 constitute a ?attened spherical
re?ecting surface acting upon the light rays as
already explained in connection with the lamp
of Fig. 1. The ?attened transmitting portion
4
9,110,590
with a mount therein, and a ?lament coiled in
Bl may be clear or frosted as desired and, of
course, may have a greater or lesser radius of
curvature than as illustrated. The stem, mount
helical fashion and arranged as a ?at loop, a por
tion of the surface of the bulb serving as an
e?icient re?ecting surface and being divided into
and lead-in wires are omitted in Figs. 1 and 2
since they may be of any conventional or com
mercial construction.
two parts, one a paraboloid of revolution which
is a surface generated by revolving a partial
parabola about the axis of the bulb and at a
-
As one example of a bulb of satisfactory shape
to accomplish the results above discussed, the
constant distance from said axis, so that the
focus ‘of the parabola transcribes a circle about
- dimension of that shown in Fig. 2 may be as fol
said axis, and said circle determining the posi 10
10 lows, where it is assumed that the "diameter of
the circular axis of the ?lament is 0.86, inch:
-
statlon
Distance 0
tion of said filament, and a second re?ecting
portion beyond the ?rst, the surface of which is
a ?attened hemisphere and shaped to re?ect the
Outside
to station bulb radius
light from one or more points on the ?lament
back to the ?lament at a point directly across 15
from the point of emission, said second re?ecting ~
15
0.15
0.50
0.25
0.00
0.25
0.50
0.15
1.00
1.25
1.50.
1.15
2.00
2.25
2.50
20
25
2.68
0. 00
1.04
1.15
portion thereby shaped to reinforce the light fall
ing on the parabolic re?ecting surface.
4. A re?ecting incandescent lamp having a
1.21
1.38
1.54
1.00
1.81
1.04
2.05
2.11
2.21
2. 31
2. 40
symmetrical bulb, a mount and a ?lament ar
faces of which the principal surface is formed
by revolving a parabola about the axis of the
mount at a constant distance therefrom so that 25
__________ -_
2.15
0.00
s. 25
3.50
s. 05
the focus of the parabola describes a circle about
the axis of the mount and this circle coincides
substantially with the circle bounding the ?la
ment, the said parabolic surface having its fo
cus relatively close to its apex and terminating
at the level of the plane containing the ?lament,
2 45
2.20
1.00
1. 01
0.00
30
In Fig. 3 is shown a polar diagram showing
the distribution and intensity of the light emitted
by the lamp of Fig. 2. This indicates a very high
the secondary portion of the re?ecting surface
being globular in shape and located between the
?lament and the base of the lamp.
intensity of light within a cone having an in
35 cluded angle of 26°, a concentric cone of rapidly
5. A re?ecting incandescent lamp including in 35
decreasing intensity out to an included angle of
its structure a bulb having a ?lament arranged
in a plane at right angles to the main axis of the
bulb, the bulb being shaped and coated to pre
sent an integral and continuous re?ecting sur
76° and an outer concentric cone of less rapidly
decreasing intensity out to an included angle of
100°. It will be understood that the light dis
face including a substantially parabolic portion 40
truncated and terminated approximately at its
focal plane and supplementediby an enlarged
globular portion located between the ?lament
and the base of the lamp, the plane of said ?la
ment coinciding substantially with the focal
plane of the parabolic portion of the bulb and
both portions of the bulb cooperating to direct
the light of the lamp in a concentrated beam,
while the'globular portion furnishes space for
40 tribution‘ indicated in this diagram is merely typ=
ical of that derived from one lamp constructed
in accordance with my invention, and that the
angles mentioned may be varied within a con
siderable range by appropriate modi?cation of
45 the bulb dimensions.
'
Having thus described my invention, what I
claim as new and desire to secure by Letters
Patentof the United States is,—
1. A re?ecting incandescent lamp having a bulb
50 shaped and coated to present a re?ecting surface
convection currents of gas tending to cool the re
which is a paraboloid of revolution expanded until
the locus of its focal points constitutes a circle
.of appreciable diameter, a ?lament located in
the plane of the focal points of said parabola,
55 and a concave globular re?ecting surface of dif
?ecting coating of the bulb ‘and so prevent dam
age from overheating.
6. A re?ecting incandescent lamp including in
its structure a symmetrical bulb having a para
bolic outer portion and a bulging elliptical inner
- ferent curvature located behind the focal plane
portion, a mount, and a ?lament disposed in a
of the parabolic portion of the bulb and shaped
single plane which is perpendicular to the axis
so as to ‘aid in re?ecting rays from the lamp in
of the mount and which includes the focus of said
a'cone of divergent rays of intensity diminishing
60 from the center outwardly.
2. A re?ecting incandescent lamp having a bulb
shaped and coated to present a re?ecting surface
which is a paraboloid of revolution expanded until
the locus of its focal points constitutes a circle
65 of appreciable diameter, a ?lament located in the
plane of the focal points of said parabola and
acting to supply a reinforced beam of light as
substantially parallel rays, and a ?attened hemi
spheric-a1 re?ecting surface located behind the
70 focal plane of the parabolic portion of the bulb
and shaped to re?ect rays from the ?lament so
that these re?ected rays reinforce the partial
focusing action of said parabolic portion of the
parabolic portion, the bulb providing a re?ecting
surface formed by revolving about the axis of the
75
re?ecting surface.
3. A re?ecting incandescent lamp having a bulb
20
ranged concentrically with respect to the bulb,
the bulb presenting cooperating re?ecting sur
50
mount, and at a distance therefrom, a compound
continuous curve, the outer part of which is a
partial parabola and the inner part of which is a
partial ellipse, the two parts of such curve having
a common focal point which lies in the said plane~ 65
of the ?lament of the lamp and describes a circle
in the revolution of said compound curve.
7. A re?ecting incandescent lamp including in
v
its structure a bulb having a coiled ?lament ar
ranged in a plane at right angles to the main '
axis of the bulb, the bulb being shaped and coated
to present an integral and continuous re?ecting
surface including a substantially parabolic por
tion truncated and terminated approximately at
its focal plane and supplemented by an enlarged
2,110,690
5
globular portion located between the ?lament ' convection currents of gas tending to cool the re
?ecting coating of the bulb and so prevent dam
age from overheating, and’ a re?ecting disk lo
plane of the parabolic-portion of the bulb and - cated in the bulb as a substantial continuation'of
'
'
5
both portions of the bulb cooperating-to direct said globular portion.
and the base of the lamp, the plane of-said ?la
ment coinciding substantially with the focal
the light of the lamp in a concentrated beam, '
while the globular portion furnishes space for
_ JOSEPH FRANCIS COOKJIRY.
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