Note: Descriptions are shown in the official language in which they were submitted.
7 7
1 l~8,105
FI,UORESCENT LAMP HAVING A TUBULAR ENVELOPE
OF COMPACT TRIDI~F.NSIONAL CONFIGURATION~
AND rlETHOD OF M~KING SUCH RNVELOPE
CROSS-REFE-RE,NCE TO RELATED PATENT
This application discloses and claims a compact
fluorescent lamp that is of triple-bent tub~lar config~
uration an~ is employed as the light source in the light-
ing apparatus disclosed and claimed in U.S. Patent No.
4,300,07~,lssued November 10, 1981, of H. Skwirut et al.
entitled "Screw~In Type I.ighting Unit Having Convoluted
Tridimensional Fluorescent Lamp,~ which patent is assigned
to -the assignee of this app1ication.
BACKGROI~D OF THE INVENTION
Field of the Invention:
This invention generally relates to electric
'``~
, ~,
3~ 7
~ 48,105
discharge lamps and has particular reference to an im-
proved fluorescent lamp of compact size and high bright-
ness that is suitable for use as a light source in various
kinds of residential and co~ercial lighting fixtur~s that
are designed for incandescent type lamps.
~c~e~lon of the Prior ~rt:
Electric discharge lamps having tubular enve-
loDes which provide "three-dimensional" type light sources
are generally well known in the art. U.S. Patent
2,652,483 granted September 15, 1953 to Laidig et al.
discloses fluorescent lamp units of helical configuration
(Figs. 7 and 15 embodiments) that are formed by coupling
several semi-circular lamps together to ~form one operative
assembly. Another fluorescent lamp of three-dimensional
configuration that is formed by four sections of conven-
tional fluorescent ]amp tubing which are "bundled" to-
gether and interconnected by suitable apertures in the
side walls of the respective tubes is disclosed in U.S.
Patent 3,501,662 issued March 17, 1970 to Plagge.
2 Electric discharge lamps having tubular enve-
lopes that are bent into various shapes to provide concen-
trated light sources are also known in the art. A double-
ended type sodium-vapor discharge lamp having an envelope
which is formed from a single tube that is folded or bent
upon itself twice to provide three straight tubular seg-
ments that are disposed in parallel triangular-spaced
relationship is disclosed in British Patent 854,745 pub-
lished November 23, 1960 (Figs. 3 and 4 embodiment). A
luminous discharge tuhe de3igned for advertising and
3 48,105
display purposes (or as a beacon light) and having an
envelope formed from glass tubing which is bent upon
itself eleven times to provide a corresponding number of
U-shaped sections is disclosed in U.S. Patent 1,898,615
: granted February 21, 1933 to Byrnes. Gaseous discharge
vi.Aes consisting of a heat-conserving housing that
encloses a lamp having a tubular envelope that is bent
u?or itself three times to provide four straight sections
which are spaced from one another and arranged so that the
lC electrode-containing ends of the envelope are located on
opposite sides of one of the curved segments or bends is
disclosed in U.S. Patents Nos. 2,001,511 and 2,200,940
granted to Uyterhoeven et al.
In accordance with the more recent proposal, a
screw-in type flourescent lamp of compact size is provided
by suitably partitioning the interior of a cylindrical
envelope or by making the envelope from tubing that is
bent upon itself to provide a U-shaped bulb, and which may
be additionally twisted into spiral shape or redoubled on
itself to provide a generally M-shaped envelope. A fluor-
escent lamp constructed in this manner is disclosed in
U.S. Patent 3,551,736 granted December 29, 1970 to Doehner
(t'ne M shaped tubular envelope embodiment being shown in
Fig. 5 and described along with the other aforementioned
shapes at lines 24-30, column 2).
A method of making a circular-shaped ~luorescent
lam~i~ by bending a straight tubular glass envelope around a
suitable curved jig is disclosed in U.S. Patent 3,993,465
granted November 23, 1976 to Hurx et al.
3'7'77
4 48,105
SIJMMARY OF THE INVENTION
. .
While the prior art electric discharge lamps
were functionally satisfactory insofar as they provided
the desired physical compactness and light concentration
by employing "three-dimensional" type envelopes, they were
~ifficult and expensive to manufacture since they either
required the use of a number of separate lamp or bulb
c~mponents that were joined together, or utilized enve-
, lopes made from tubing which was bent in such a way that
lr~ the electrode~containing ends of the tubing were located
at opposite ends of the convoluted envelope or on opposite
sides of one of its U-bent segments. This not only com-
plicated the base and terminal structures required to con-
nect the lamp electrodes with a suitable power source, but
made it very difficult or impossible to provide the lamp
with a screw-in type base which would permit the lamp to
be used in lighting fixtures designed for incandescent
type lamps. In addition, some of the prior art lamps also
required tubular envelopes of such complex shape that
their manufacture on a mass-production basis would be
impractica] from both a cost and quality standpoint.
The foregoing difficulties and problems are
solved in acco-rdânce with the present invention by fabri-
` cating the envelope of the discharge lamp from a single
piece of vitreous ~ubing that is bent into three conjoined
U-shaped sections which are so oriented that the ends of
the tubing which contain the electrodes are disposed
adjacer.t one another in a common plane that does not
intersect any of the U-be~d segments of the envelope.
~.
~ 3'7~7
: 5 48,105
This is accomplished by orienting the U-shaped sections of
the envelope in such a manner that two of them are dis-
posed in paired side-by-side relationship and are joined
by the third U-shaped section which is inverted and lo-
cated in a plane that is parallel to the plane containing
ttle ~ree ends of the tubing. The spatial relationship of
the three U-shaped sections of the novel envelope is
~cco~di;lgly such that two of them form a pair of spaced
. hooks or "crooks" that are aligned with one another and
have their tips laterally bent toward each other and
joined by a U-bend which forms the third U-shaped section.
The straight tubu].ar legs of the U-shaped sections are
thus disposed in rectangular columnar a~rray and the free
ehds of the envelope are located proximate and on the same
side of the U-bend which connects the tips of the paired
: "crooks."
The resulting triple-U-bent envelope is thus of
, three-dimensional. configuration and, while very compact,
still provides a single discharge channel that is more
2~ than four times the length of one of the straight legs of
the convoluted envelope. The u~ e shape of the "dual-
C~C-~ 'r~ Y~g ~r
crooked" envelope t~h~s provides a tortuous discharge path
which is not only of sufficient length to permit the lamp
to be operated efficj.ently at a practical power loading
but is so confi.gured that the electrodes are located at
the same end of the en~elope and so oriented that the
enve1ope can readily be fitted with a screw-type base and
s.ili provide a lamp that is sma~.1 enough to be used in
lightin,n fi.xtures de~igned fo-r incandescent type lamps.
7~7
6 48,105
me spaced tubular legs of the triple-U-bent
envelope also provide an air space between each of ths U-
shaped sections and a "chimney-like" central opening which
prevent~ the lamp from becoming overheated, especially if
it is oper~ted at hlgh power loadings in a confined environ-
ment. The "free-standing" orientation of the U-shaped
sections also permits the envelope to be readily manufac-
tured ~rom glass tubing of the t~pe employed for conven-
tional flourescent lamps by heating the tubing to make it
plastic and then sub~ectîng it to two bending operations
which rapidly form all of the U-bends while the glass
tubing is still soft and pliable.
Since the electrode-containing ends of the
envelope are located ad~acent to one another and on the
same side of the medial U-shaped section, these parts of
the envelope can al~o be read~ly coupled to each other by
suitable bracing means to rigidify the lamp and prevent
the envelope from breaking while the finished lamp is
being handled or shlpped.
: 20 ~RIEF DESCRIPTION OF THE DRAWINGS
A better under~tanding of the invention wlll be
obtained from the exemplary embodiment shown in the ~ccom-
panying drawings, wherein:
Figure 1 is a pictorial view of a compact fluor-
escent lamp that embodies the invention and employs the
triple-~-bent envelope of the type produced by the invention;
Figure 2 is an enlarged fr~nt elevational view
of the lamp shown in Figure 1, portions o~ the envelope
being removed for illustrative purpo~es; and
,. ...
~,
7~'7
7 43,105
Figures 3 and 4 are simplified pictor~al views
illustrating the manner in which a straight piece of
vitreous tubing is formed in~o a triple-U-bent lamp enve-
lope by only two sequential bending operations.
While the present invention can be advantageous-
ly employed in various kinds of electr~c discharge lamps
that are suited by virtue of their small physical size and
high brightness ~or lighting homes or offices, it is
particularly adapted for use in conjunction with low-
pressure type dlscharge lamps such as fluorescent lamps
and it has, accordingly, been so illustrated and will be
so described.
The compact fluorescent lamp L shown in Figs. 1
and 2 employs an envelope 10 that is compo~ed of suitable
light-tran~mitting vitreous mater1al, such as glas~ tubing7
that is shaped to provide a tortuous discharge channel which
` extends between a pair of electrodes 12 and 14 (see Fig.
2) sealed within the ends of the en~elope. As will be
noted, the tubular envelope 10 is bent upon itself three
times in such a fashion that it has three generally U-
shaped sections which are located in three dif~erent
planes and oriented so that two of the sections are
aligned with one another in paired side-by-side relation-
ship and joined by the other U-shaped section which is
inverted. One of the paired U-~haped sections is defined
by a substantially straight tubular segment 16 that is
joined by arcuate segment 17 to another straight tubular
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3~ 7
8 48,105
segment 18. Tubular segment 18, in turn, is joined by
another arcuate segment l9 to another straight segment
20---thus forming a second U-shaped section that is lo-
cated in a plane which is substantially normal to the
plane of the first U-shaped section. Straight segment 20
s Joined by a third arcuate segment 21 to another
straight segment 22 and thereby forms a third U-shaped
section that is located in a plane which is substantially
normal to the plane of the second o medial U-shaped
section and is substantially parallel ~o the plane of the
first U-shaped section.
As shown mosr clearly in Fig. 1, each of the
arcuate segments 17, 19 and 21 of the c~onvoluted envelope
10 are U~bends of such curvature that the straight tubular
segments 16, 18, 20~ and 22 extend in the same direction
and are disposed substantially parallel to one another in
quadran~ular and columnar-spaced array. The straight
segments 16 and 2~ which contain the lamp electrodes (and
thus terminate the discharge channel and the envelope 10)
- 20 are located proximate one another in a common plane that
is substantially parallel to the plane of the inverted
U-shaped section which is formed by the straight segments
1.~ and 20 and the medial U-bend 19. The straight tubular
segments 16, 18, 20, and 22 are thus arranged in pairs
that are located in fou- different planes which are so
oriented that adjacent planes are mutually perpendicular
to one another. As a result, the overall configuration of
~he triple-U-bent envelope 10 is such that it is generally
c~r~ical or tetrahedrai in character. When the fluorescent
3'7~7
9 48,105
lamp L is energized, the envelope 10 thus provides a
three-dimensional light source which i5 quite compact but
still provides a single discharge channel that i~ consider-
ably longer than four times the overall height dimension
"h" of the convoluted envelope 10 and thus permits the
lamp L to be operated very efficiently.
As will also be noted in Fig. 1, the straight
leg segments 16 and 22 which terminate the envelope 10 and
the discharge channel are fitted with suitable base mem-
bers 24 and 25 that are secured to the sealed ends of theenvelope by cement or other suitable means and carry a
pair o~ terminals such as metal pins 26 and 27 that are
connected to the respective electrodes. me orientation o~
the three U-shaped envelope sections is such that the
based ends o~ the straight segments or legs 16 and 22
of the envelope 10 are located on the same side of the
U-bend segment 19 that constitutes part of the inverted
U-envelope section. This spat~al arrangement not only
e~fectively makes the lam~ L of single-ended construction
(and thus greatly simplifies connecting the lamp to a
suitable power source) but permits the envelope 10 to be
easily rigidified and protected from breakage by a suit-
able bracing means such as a strut 28 fashioned from rigid
wire or other suitable material. The strut is secured to
the base members 24 and 25 and laterally extends to U-bend
segment 19 to which it is coupled, as by a slip-interlock
type of fit effected by an arcuate hook 2g that is pro-
vided at the end of the strut and grips the U bend 19. As
shown, the bracing strut 28 can be fabricated from a
~:,f
48,105
sin~le piece of wire (or other rigid material) that is
bent upon itself and prevented from fle~ing by a cross-
piece 30 that is joined to the ends of the strut which are
secured to the base members 2~, 25.
As shown in the enlarged view of the fluorescent
l-~nlp L illustrated in Fig. 2, the triple-U-bent envelope
10 is provided with the customary inner coating 11 of a
suitable phosphor material that converts the ultraviolet
radiation produced by the discharge into visible radiation
The terminating legs or segments 16 and 22 of the envelope
are hermetically sealed by stem assemblies 13 and 15 of
conventional construction that are fused to the envelope
and carry the thermionic electrodes 12 and 14. The elec-
trodes comprise the usual tungsten wire coils that are
coated with electron-emission material and are electri-
cally connected by lead wires 35 and 36 to the pin termi-
nals 26 and 27 of the respective base members 24, 25
fastened to the sealed ends of the envelope. In accord-
ance with standard lamp-making practice, the envelope 10
contains a suitable ioniæable medium such as a fill gas
and a dose of mercur~77 thac are introduced into the enve-
lope through a tubulat:ion 23 that extends within stem 15
and is subsequently tipped-off and sealed in the usual
manner. A suitable fiil gas is argon at a pressure below
about 10 Torr, and preferably about 3 Torr. The mercury
dosage will vary accordin~ to the physical size of the
envelope 10 and the power loading at which the lamp L is
operated The mercury dosage is sufficient to provide
~,~rcury vapor at a partial pressure of from about 6 to 10
'7'~7
11 48,105
milli~orrs when the lamp is operated at its rated wattage.
While any suitable phosphor or admixed phosphors
can be used to form the inner luminescent coating 11, in
lighting applications where optimum visual clarity and
color rendition of the illuminated objects or scene are
requi.red, coatings which contain a blend of three phos-
phors that emit visible radiations in three different
se1ected regions of the spectrum (specifically, the wave-
leng~h regions of about 450 nm, 540 nm and 610 nm) are
desirably employed to provide a so-called "prime color"
.luorescent lamp, pursuant to the teachings of W. A.
Thornton in the article entitled "Luminosity And Color-
Rendering Capability Of White Light"~ Journal of the
Optical Society of Anlerica~ Volume 61, ~o. 9 (September
1971), pages 1155-1163. As a specific example, a suitable
phosphor blend for a fluorescent lamp having such an
enhanced light output contains manganese-activated zinc
silicate, europium-activated strontium chlorophosphate,
and europium-act:ivated yttrium oxide phosphors---all of
whi^h are well known to those skilled in the art.
As iliustrated in ~ig. 2, the wire brace 28 has
two laterally deper.ding legs 31 and 33 that extend through
suitable openings in thf base members 24, 25 and are
terminaLed by arcuate segments 32 and 34 which nestingly
seat within the base collars and securely couple the brace
to the based ends of the envelope 10. The hooked end 2f?
of rhe brace 28 slips over and interlocks with the U-bend
segment 19 l:ha~ is located opposi~e the based ends of the
enve'.o}e, as previously described.
3'77~7
12 48,105
; _VELOPE MAN7~FACTURE (FIGS. 3 AND 4)
An important feature of the invention is that
the configuration of the convoluted en~7elope 10 is such
that it can be readily manufactured from a straight piece
of glass tubing by only two bending operations (illus-
trated in Figs. 3 and 4) and a single heating operation,
all of which can be performed efficiently with automated
,~?chines. The first tube-bending operation is shown in
~ig. 3 and consists of first placing a straight piece 10'
of suitable glass tubing of predetermined length in a pair
of holders 38, 40 which grip the end segments of the
tubing and are swingable toward one another along arcuate
paths (as indicated by the arrows) in~ a plane that is
substantially aligned wiLh and contains the tube axis. As
a specific example~ soda-lime glass tubing of the type
conventionally used in the manufacture of fluorescent
lamps can be employed. Such glasses are well known in the
art and typically have a softening point in the order of
693C, an annealing point of about 515C, and a strain
point of around 470C.
After the glass tubing 10' is placed in the
holders 38 and 40~ the medial portion of the tubing ex-
tendillg between the holders 38 and 40 is heated by gas
fires (or other suitable means) to a uniform temperature
which softens the glass sufficiently to permit the tubing
to be ~ent without fracturing or collapsing. A tempera-
ture of around 780C is suitable in the case of the afore-
Mentioned soda-lime type glasses. The center of the
~ubing 10' is then place~ against the arcuate work surface
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13 48,105
of a preheated mold colllrc,nent 42, which surface is con-
toured to define a peripheral groove 43 that nestingly
accommodates and effects a mechanical interlock with the
tubing, While the glass is in its heat-softened condition,
. holders 38 and 40 are rapidly swung through an arc of
~pproxima-tely 90, in the manner indicated by the arrows,
thus bending the central part of the heated tubing 10'
- around the mold 42 and forming a U-bend 19 that transforms
the straight tubing into a U-shaped tubular component 10"
which has long leg sections that are substantially paral-
lel to one another and CI the same length, As indicated,
the segments of the U-shaped tubing 10" immediately adja-
cent the U-bend 19 constitute the tubular segments 18 and
20 of the finished en~7elope 10, and the rigid end segments
16 and 22 of the tubing that are gripped by the holders 38
and 40 constitute the corresponding tubular segments which
terminate the finlshed envelope.
The second bending operation is depicted in Fig.
4 and is begun immediately after the first bending opera-
tion is completed while the glass tubing is still in itsheat-softened ~nd plastic condition. As shown, the legs
of the embryonic U-shaped envelope component 10 " are
sea~ed ~gainst the edge of the working surface of another
prehea~eG mold component 44 that is reciprocally movable
(as indicated b~7 the arrows) and indexed into bridging
posit-on with both legs after the first bending operation
ha, beer, cc:mpleted. As will be noted, the working surface
o ~ seccr.d mold 44 is also of arcuate configuration and
ccn.~urec, to pro~7ide a pair of channels or grooves 45 and
3 1 ~
14 48,105
46 that are spaced to nestingly accommodate the legs of
the U-shaped tube component 10" and thus serve as guides
during the second bending operation.
Immediatel~7 after the U-shaped tube 10 " is
seated against the rim of mold 44, t7r.- holders 38 and 40
ng with the gripped tube ends 16 and 22) are heid
stationary and mold component 42 and the U-bent end 19 of
the tube 10 " are swung through an arc of approximately
1~0 (indicated by the arrow) along a plane that is sub-
stantially normal to the plane of the first bending opera-
tion, thereby effecting the second bending operation. As
shown, the bending action is such that selected medial
portions of both legs of the tube 10 " are wrapped around
the grooved portions of the second mold component 44 and
formed :into two additional U-bend segments 17 and 21 that
are spaced from each other and disposed in substantially
parallel-paired relationship. The mechanical interloclc
with the tube lC " effected by the grooved working surface
of mold component 42 is such that mold component 42 grips
the U-bend 19 sufficientl~ to permit the mold to apply the
necessary tor~ue to the tubing for the second bending
operation when mold 42 is swung through the aforesaid arc.
.~s will be noted from the phantom showing in Fig. 4, the
second bending opera~ion places the first-formed U-bend 19
adjacent the end segments 16 and 22 (the latter being cut
way for illustrative purposes) and completes the forma-
tior. o~ the finished convoluted tubular envelope 10.
~ tile the glass tubing is still hot and plastic,
a s~ream of inert gas (such as compressed air) is prefer-
~ 7~ 7
48,105ably introduced into one end of the tubing to produce a
positive pressure and "round out" any deformities in the
circular shape of the tubing which may have occurred
during the bending operations, especially in the U-bent
segments.
If the tubular envelGpe lO is still in heat-
softened condition, it is then subjected to a stream of
co~l air to set the tubing in its new shape. Mold com-
ponent 42 is then lowered, rotated 180 and withdrawn.
Molc' component 44 is also manipulatecl. to free it from
U-'bends 17 and 21 and withdrawn from the envelope lO.
Holders 38 and 40 are opened and the released triple-U-
bent envelope lO is then transferred to a suitable anneal-
irg apparatus and subsequently subjected to the sealing-in
operations, etc., required to transform it into a fluores-
cent lamp.
For ease of manufac~ure, the straight piece of
glass tubing 10 ! iS provided with an inner coating of
phosphor (not shown in Figs. 3 or 4) before it is heated
and sub~lected to the two bending operations. However, if
optir.l~1m light output from the finished fluorescent lamp is
desired, then the phosphcr-coating operation is performed
after a- clear glass length 5f tubing is reshaped into the
desirecr~ trip1e-lT-be~t configuration since this would
increase the lumen output of the finished lamp by approxi-
matel ~
If the envelope lO is ~o be made in the manner
.c~ ed abov--, it is imperative that the glass tubing
~:' be uni formlJr heated to the proper temperature before
7~ 7
16 48,105
the bending operations, and that all of the U-bends be
made very rapidly before the glass begins to cool and
r, rigidify.
- Uniform heading of the medial portion of the
tubing lO' is best accomplished by continuous rotation of
t.~e tu~ing on rollers over an open burner or in an oven
whlch are designed to keep both ends of the tubing cool
and rigid so that the heated tubing can be transferred to
arld gripped by the movable pair of holders 38 and 40.
The fact that the last two U-bends 17 and 21 are
made simultaneously, pursuant to the invention~ enables
the tube-reshaping process to be performed in a very short
period of time (in the order of from~ about lO to 20
seconds)---before the glass has cooled to a point that the
tubing begins to rigidify. In addition, the tube-holders
38 and 40 and the mold components 42 and 44 are so con-
structed that they can readily be made parts of a single
machine having drive means, indexing units, etc., which
actuate and move the holders and molds in the proper
~equence automatically in a very precise and controlled
manner---thus reducing the time required for the tube-
bending operations to a minimum.
_PECIFIC EXAMPLE
Fo].lowing is a specific example of a compact
tridimens~onal fluorescent lamp which embodies the fea-
tures of the present invention.
A conventional 40 watt fluorescent lamp having a
'IlO t~pe envelope (approxi.mately 32 mm. outside diameter)
a~d a-- overalI lengrh (unbased) of about 4 feet (approxi-
17 48,105mately 122 cms.), when bent into three U-shaped sections
of substantially the same length and curvature, forms a
generally rectangular convoluted lamp which has an overall
height of about 9-3/4 inches (24.76 cms.~ and a width
dimension of about 5-1/2 inches (13.97 cms.) along each
~;.r.'e with a 3 inch (7.62 cms.) spacing between each of the
adjacent legs of the U-bent sections. Since the lumen
OU~p~lt (published) of a conventiolla]. 40 watt T10 rapid
st:art lamp is 3200 lumens and the lamp has a published
lC life of 18,000 hours, it ~ill provide a triple-U-bent lamp
of the foregoing dimensions that has the same useful life
and only a sl.ight decrease in lumen output (perhaps a loss
of 350 lumens) due to the masking or light-blocking effect
of the juxtaposed legs of t;rie U-sections.
Hence, despite its very com.pact size (approxi-
mately ~4-1/2 cms. by 14 cms.~, the aforementioned triple-
U-bent lamp provides a light source which will produce
about 2850 lumens at an efficacy of around 57 lumens per
watt (when operated on a conventional rapid start ballast)
that consumes about 10 watts) and have a useful life of
appro.Y~marely 18,Q00 hours. The cost savings and power-
conscrvation advartages derived from such a convoluted
~;luol-escent lall;p are accvrdingly quite substantial com-
pared to a ].50 ~,ati incandescent type lamp that produces
around 28')() lumeIIs at an efficacy of about 18 or 19 lumens
per watt and ha~ an average life (published) of only 750
ours .
As wil~ be apparent to those skilled in the art,
riple~ bent lamps of the present invention can be
37~77
18 48,105
fabricated from glass tubing of various diameters and
lengths to provide a new family of compact tridimensional
low-pressure discharge lamps that can be used as cost-
saving and energy-saving replacements for incandescent
lamps now used for general lighting applications in many
d-fferent kinds of fixtures (table lamps, floor lamps,
etc.).
