Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
COMPACT FLUORESCENT LAMP WITH
C~.PP.~-ARC EXCI~ATION
Back~round of the ImTention
This invention rela~es ~o fluorescent lamps and
more parti::ularly to fluorescen~ lamps corltainiTIg an interior
arc discharge tube. Moreove~, the present in~ention also
0~ relates to a combination fluorescent and arc discharge
lamp in which the l~ght ou~put may be var;ed as between
light from ~che arc an~ light from the p~osp~o~.
At present) much of present-day lighting needs axe
supplied throu~ the use of iFIefficient incandeseent la~ap~.
While these lamps are relatively in~cpensive and are
produced~ in large quantities with knowrl technolo8;y, nonet:hele~s
the increasing cost of electric energy has, in rece~ years,
chaDged the econo~nic situation. In particular, i the
cost of operating ~ncandescent lamps is considered, along
with their relat~vely short lifetimes, the incandescen~
~ may be uneconomical in certain situations parti ularly
those in which they are compared agalnst long life, high effi-
ciency lamps. A number of different kinds of lamp geometries
and designs have at~empted to ulill this need,
Conventional fluoresee~t lamps, in wh~eh the
vi~ible radiation is prod~ced by a phosphor coating on the
nterior of a partially evacuated disrharge tube, are
eficient and long lived but lack the geometry necessary or
use in standard luminaires and fixture~s,
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Another potential incandescent lamp replacement
is the solenoidal elec~cric field lamp (Sl:F ~ amp) which is
similar in operation to a fluorescent lamp but in which
an electronic ballast drives a ferrite core disposed wi~hin
05 an arc discharge medium to produce ultraviolet radia~ion
which impi~ges upon a phosphor coate~ upon the 1æmp tu~P
w~ll S9 as to produce the des~red radiation. Ihese lamps
are smallt c~mpact and, with an appropriate electronic ball~st,
easily replace the con~entisnal incandescent lamp in most
fixture~/ It is not, h~wever, an arc lam~ in which the
prlmary llght source ls from the arc discharge, Rather, it
is a fluorescent lamp in which the primary light source i5 a
phosphor material.
Another s~ cant candidate for a lamp ~o
replace the incandescent ~ulb is the ~ ~ developed by
~he pre~ent assignee. ~ ~ is a trad~ark of the General
Electric Company, Cleveland~ OH, In this lamp, the light
output is provided solely by the ~islble electromagne~ic
radlation frGm the arc discharge tube itself, which is
20 surrounded by an outer jacket for protectiorl and for the~nal
insulation purposes. In ~he HALARC~) lamp, the ra~ed ou~pu~
color spectra is a function solely o~ the arc tube ingredien~s
and the operating conditions,
Lastly, another possible replacemen~ ~or the
25 in andescent lamp lncludPs such lamps as the folded discharge
l~mp, in which a converltional fluorescent lamp is desi~ned
and built with a long discharge path length formed by folding
or otherwise reconfiguring the discharge ~ube,
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A signific.ant difference between ~he lamp of ~he
present invention and other lamp designs is that, in the
lamp of the presen~ invention, ~he arc discharge ultraviolet
source is physically isolated from the phosphor as opposed ~o
05 conventional fluorescent lamps where the glow discharge
ultravioLet source is in contact wi~h the phosp~or.
Accordingly, the glass part of a convelltional 1uorescen~ l~mp
may be best be described as a discharge envelope. The glass
employed in such a lamp ~s not cri~ical. Howeve~, in lamps
which produc~. their prlmary ~isible light output f~om an arG
discharge, rather than from a phosphor, the arc tube mNs~
typically be operated at relatively high temperature rangin~
for example, from approximately 400 C to approxim~tely
900 C. For sueh high ~emperatures hard glasses may be-
required, particularly for temperatures in ex~ess of
approximately 700C, At lower opera~ng temperatures, say
for example 600 C, a softer, less expensi~e glass may be
~mployed for the arc tube~ ~dditionally, con~entional
fluoresce~lt l~mps generally operate at a total internal vapor
pressure of less than 3 torr, This vapor pre~sure ar~ses
fr~m a partial pressure o~ less than approximately 3 ~orr
for argon and a partial pressure of mercury of between 1
a~d 10 millitorr. In contrast, l~mps of the presen~ i~ven~ion
pre~erably operate with total arc tube vapor pressure of
between app~ox~ma~ely 1~0 and approx~mately 3000 torr. This
~o~al pre~sure arises from partial pressures o argon,
mercury and copper halide.
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Ano~her lamp ha~in~ a structure resembling the
present invention ls the so-called color-corrected mercury
lamp. In this lamp at least 80 percent of the light ou~put is
from a mercury arc. There is also presen~ some light output
05 fr~m a phosphor coatlng an exterior enclosing envelope.
Ho~ever, in such l~mps only about 10 to 15 pereent of the
light output is due to the phosphor coating. Such lam~s use
~he phosphor to ~odify the color perception of the light
produced by the arc. In such lamps the ultra~iolet ou~p~ttfrom
10 the arc tube i5 low. In contrast, the ultraviole~ ou~pu~
of the present invention is enhanced and controlled to produce
ul~ra~iolet radiation having ~pecific wavelengths (typically
ln excess of 300 nanometers) to promote transmissi~ity thro~gh
glas~, notably the harder glasses. This pr~motes con~rollable
light production fr~m the phosphor and from the arc ~oo.
~ nother si~nificant fact concerning ~he presen~
~nYention is that glass is ~ften not vei~ tran~missi~e for
ultra~lole~ radiation. Accordingly, thç selection o
radiating discharge medium species which may be ineluded
in the arc tu~e is not trivial. Not only ~st the species
radia~e a~ the proper wa~elength to assure opt~mum ~rans-
mi~sivity throùgh the arc tube, but it should a~so radiate in
a fairly narrow band of the spectrum in order ~o provide
higher e~flciencies. Further more, the discharge medium
mNst be easy to work with and nonreacti~e with the arc
; tube material e~ployed. Furthermore, the ~apor pres~res o
the radiating species employed should have desir~ble values
within the range of operating temperatures employed.
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Summary of the Invention
In accordance wq~h a preferred embod~ment of
the present in~ention a fluorescent arc lamp c~mprises a gas~
tight, ultraviolet-transmissive arc tube wl~h electrodes
05 dlsposed in either end, and an exterior visible-light ~ransmis-
siYe gas-tight en~elope en~losing the arc tube; the envelope,
having an ultraYiolet ~ensitive phosphor eoated thereon w~th
conductors disposed through the envelope for electrical
eonnection between said electrodes and an ex ernal s~uroe of
electrical energy. F~rthermore? in accordance with this
embodiment the arc tube has disposed therein a vaporizable
discharge medi~m camprising materials selected from the halides
of copper, silver, and rhenium.
Furthenmore, in accordance with a furthe~ em~odimen~
of the present invention, mercury is also disposed within
the arc tube. The use of varying proportions o mercu~y
within the arc tube permits the construction of an e~tire
range of combination "fluorescent/arc-discharge lamps in
which the visible radiation is pr~duced not only from the
phosp~or, but also from the arc discharge wi~hin the arc
~u~e itself. By increasing the pro~o ~ ion of mercury
wi~hin the arc ~ube, the lamp of the present i~vention
tends to exhibit lamp eharaeteristics more closely assoelated
with lamps whose sole visible light outpu~ ar Pes from the
arc discharge itself.
~ ccordi~gly, it is an object of the pre~ent
inYPntion to pro~de an efficient re~lacement for the incan-
d~cent lam~.
~ ~05 ~ 3 .
It is a further object of the prese~t inventisn
to provide 8 combination fluorescent and ~rc discharge
lamp in which the arc discharge is physically isolated from
the phosphor.
05 . It is also an object of the prese~t in~ention to
providP a range of lamp~ in which the proportion of li~h~
produced by the arc dlscharge as compared to the portion
produced by ~he radiating phosp~or, can be varied.
Las~ly, in sum it is an object o~ the presen~
~- 10 invention to produce an eficient long life l~mp, operable
~n a~y position.
Descripti n of the Fi~u~es
The subjec~ matter which is regarded as the in~ention
i9 particularly pointed out and dis~inctly claimed in ~he
~15 concluding portion of the specification. The inven~ion,
b~t~ as to organization and method of practice, together
with further objec~s and advantages thereof, ma~ besll: be
unders~ood by reference t~, the following description ~aken
in connection with the accompanying drawings in which:
FIGURE 1 is a partial cross-sec~ional side eleYatio~
vi~w of a la~..p ~.anufactured in aecordance with the pre3en~
~vention.
. FIGUR~ 2 is a partial cross-sectional side elevation
vlew lllustrating a detailed view o the arc tube ~wn in
FIG. 1.
.
FIG. 1 illustrates one embodimen~ of the present
~nvention in ~hich the outer jacket 12 and a~c tube 20
are conigure~ ln the general size and shape of the above-
described HALAR ~ lamp. ~owever, the lamp of the pre3en~
` inven~ion may a~sume a lar~e range of sîzes and shapes.
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- In FI(:. 1, lamp 10 is seen to possess an outer
jacket or envelope 12 having interior phosphor coat 14. The
exterior e~velope 12 is gas-tight and transmissive to light
at visible waveleng~hs, at ~east in those embodiments of
05 the present i~vention in which phosphor 14 is disposed on
the interior of the envelope. Outer jacke~ 12 m~y be
co~veniently fastened to base 17,
Envelope 12 surrounds arc tube 20, which is more
particularly described and discuss~d in FIG. 2 below.
Arc tube 20 is a source of radiation at specific ultraviolet
wavelenths and m~y comprise either relatively hard or
relati~ely soft glass depending upon the operating temperature
of the lamp. Arc tube 20 is supported within jacket 12 by
means o~ stiff electrode lead~ 18 and 19, as shown in F~G. 1.
Leads 18 and 19 are also electrically and mecha~ically
connected to leads 16, which pass through the w~ll of jacket 12.
In a preferred embodimen~ of the presen~ in~ention jacke~ 12
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include~ a relatively thiek glass base 17, through whl~h
elect~ode leads 16 pass and which also serves as a stable
2~ pla~f~rm for fixedly mounting arc tube 20 wlthin jacke~ 12.
As is conventionally known in the art, elèctrodes 16
~yp~cally co~prise or are coated with a meta~ composition.
such a to which the glass in platform 17 is particularly
adherent. In this way the gas-tlght integrity of ou~er
en~7elope 12 is maintained. As is also well-known in the
l~mp arts, electrodes 16 are coupled in a conv~entional
manner to an appropriate electronic ballast which opera~e~
~o supply starting and running voltage for ~hé lamp.
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A number of phosphors might be employed as an
interior coating on ~acket 12. The principle requirement
for these phosphors is that they absorb radiation in the
ultraviolet region and reradiate visible light. For example,
05 but without limitation, these phosphors may include such
compounds as yttrium vanadate doped with europium (YV04:Eu),
zinc silicate-germanate doped with manganese ~n2(SiGe)O4:Mn,
and magnesium germanate doped with manganese (MgGeO4:Mn).
Space 15 between arc tube 20 and outer envelope 12 preferably
comprises a vacuum for the above-mentioned phosphor ma-terials.
A vacuum is also preferred whenever a phosphor coating 14 is
employed in which the phosphor is most efficient when
operating at or near room tempera-~ure. In other embodiments
of the invention in which phosphor coatings 14 are employed
for which the phosphor exhibits higher efficiencies at
elevated temperatures, space 15 preferably includes inert
gas such as nitrogen or argon so that some convective and/or
conductive heat flow may be provided to the phosphor
coating to permit arc tube 20 to provide the desired operating
temperature for the phosphor coating.
FIG. 2 more particularly describes the construction
of arc tube assembly 20 which preferably comprises a gas-tight
ultraviolet transmissive tube 22 with an interior space 28
having electrodes 24 exposed at either end thereof.
Electrodes 24 may actually comprise enlargements of
the ends of electrode leads 18 and 19 which are
disposed -through the arc tube 22. In order to provide
a gas-tight seal, a portion of leads 18 and 19
is a foil of metal 21 which is specifically chosen to
form a gas-tight adhesive bond both to the metal of the
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electrode leads and to the glass of the arc tube. Such
foil 21 typically comprises molybdenum.
A significant aspect of the present invention ls
the inclusion within the arc ~ube of an appropria~e ~mount
05 o a vaporiza~le discharge medium. For ex~ple, ~his medium
may.be disposed within the arc tube 20 as a pe~let 30. In
accordance with a preferred embodiment of ~he present
inven~ion the discharge medium comprises either copper hal~de,
rhenium halide, or silver halide. Howe~er~ co~per halide
is ~he preferred choice since rhenium and silver are no$ as
easy to work with in their halides forms. ~owever, ei~her
copper bromide or copper iodide may be e~ployed to produce
the desired ultraviolet ou~put from arc ~ube 20. Copper
ro~ the halides exhib~ts a s~rong and efficien~ ou~pu~
at a wavelength of 327.4 and 324.7 nan~metexs. Furthermore,
e~en though ~heir halide~ may be dificult to work with,
bot.h rh~nium and silver exhibit ultraviolet radiation at
appropriate ~avelengths and may be employed in the lamp of
the prese~t inve~tion, In particular~ rhenium exhibi~ ul~ra~
vlolet radiation ha~ ng a wavelength of 346.5 nan~meters.
Likewlse, silver exhibits ultraviolet radiation at a wave
length of 328 nanometers. Magnesium has been sugges~ed in
~he past as a radiating species; howe~er~ magnesium has a
s~rong resonance line at 285.2 naometers, bu~ this radia~ion
is absorbed by mos~ plastics and glasses m~king i~
ess desirable for the use in ~he present inven~ion.
For example, i copper iodide is em~loyed in
pellet 30, and if the lamp is operated at a reservoir
temperature between approximately 500 C and approx~m~ely
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900C, the copper iodide exhibits respectively correspondiny
vapor pressures of between approximately 1 and approximately
100 torr. However, the preferred operating temperature of
the present lamp is approximately 600C. At this temperature
05 an arc tube comprising relatively expensive fused quartz
is not required and a less expensive, hard glass may be used
for arc tube 20.. Additionally, it is also desirable to add
small amounts of argon or other noble gas to arc tube 20
for the purpose of facilitating lamp starti~g. However, such
noble gases may be added for other purposes and in amounts
which vary according to the function desired.
I~ one preferred embodiment of ~he pxesent inve~-
tion, copper halide is added to arc tube 20-along or with small
amounts of noble gases. In such an embodiment, arc tube 20
generates ultraviolet radiation at a wavele~gth which readily
passes through the glass of arc tube 20 to impinge upon
phosphor 14 on the inner wall of jacket 1~. Accordingly, in
this embodiment all of the vi~ible waveleng~h outpu~ is du~
to-the phosphor. However, i~ should be appreciated that
the lamp of this embodiment is not only a fluorescent lamp
but it is also, in fact, an arc discharge lamp and is thus
re~erred to herein as a fluorescent~arc-discharge lamp.
.. In accordance with another significant embodiment
of the present invention, arc tube 20 m~y also contain small
r ~ 25 am~unts of mercury, such as may be supplied by droplet 26
disposed within arc tube 20. The amount of mercury chosen is
generally sufficient to maintain a partial mercury vapor pres-
sure of from about 0.1 to 10 atmospheres at operating temper
atures. m e use of mercury as an added species in the
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discharge medium significantly alters the nature of the lamp.
In particular, with increasing amounts of mercury disposed
within arc tube 20, more and more visible wavelength rad-
iation is produced within the arc tube. ~hus it has been
05 found that under certain operating conditions and proportions
of ccpper iodide and merc~lry, significant amounts of
visible radiation come from mercury in the discharg~, as well
as from surrounding phosphor 14. Under other conditions, the
mercury radiation may be suppressed, resulting in behavior
. 10 re closely resembling that o~ a conventional fluorascent
lamp rather than in behavior describable as a combination
fluorescent and arc.lamp. Thus based on arc tube ingredients
and operating conditions, a whole range of lamps combining
light output from arc and phosphors excited from ultraviolet
radiation from the arc is possible. Near tha arc-end o~ this
range of lam~ behaviors, lamp~ of the present invention
become similar to color-corrected mexcury lamp5 in which
about 10 to 15 percent of the light output arises from the
pho~phor. In the present lamp, however, at least 20% of the
~- ~O vt~ible light output is derived from the phosphor. At ~h
other end of this behavior range is the above-described embodi-
ment of the present invention in which only silver, copper,
or rhenium halides are employed as ultraviolet radiating
species.
In the lamp~ of the present invention, the copper,
rhenium or silver halide is added in a quantity, depending
on volume, sufficient to produce a partial vapor pressure of
~ from about 1 to about lO0 torr corresponding to reservoir
; operating temperatures between about 500 to about 900~C,
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typically between about 0.05 mg/cc and 2 ms/cc of arc tube
volume. If mercury is used as an additive, it is chosen to
be present in an amount t~ produce a partial vapor pressure
between about 0.1 and about 10 atmospheres~ For argon9 vapor
05 pressures of from about 2 to about 100 torr are employed for
the purpose of improved lamp starting characteristics, as
is conventionally known.
While the preferred embodiment of the present
invention disposes phosphor 14 on the interior of jacket 12,
it is also possible to employ a phosphor coating on ~he
exterior of jacket 12. If such a configuration is employed~
it is~ of course, d2sirab1e that the glass of envelope 12
be transmissive to the ultraviolet radiation from arc tube 20.
Moreover, in this con~iguration it is also desirable th~t
~ 15 some form of protective coating, such as clear plastic or
glass, be disposed over the phos~hor.
There are a number of features of the present
invention which provide significant improvement over o~her
: light sources. In particular, the arc from the copper halides
. 20 produces resonance radiation very efficiently~ The o~her
copper radiation lines are very feeble compared to the reso-
nance lines at wavelengths of 324.7 and 327.4 nanometers.
Additionally, the vapor pressures of copper iodide and copper
bromide are several torr at 600~C and thus the arc tubes o~
the present invention may be operated at this temperature
rather than the 750C temperature usually re~uired for meta~
halide lamp~. This lower temperature further serves to
reduce the loss caused by infrared incandescence of the axc
tube. In particular ! in the present invention this loss is
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cut in half. Moreo~er, the lower operating tempera~re
permits the use of a softer ~lass, such as borosilica~e
glass, in place of a ~used quar~z arc tube since this and
simila~ glasses may be used at temperatures up to abou~
05 700Q C. At the same t~me, these glasses transmit the
relatively long waveleng~h ultraviolet at approxima~ely 32S
nanometer with negligible at~enustion. ~he use of these
glasses in place of fused quartz reduces bo~h ~aterial a~d
abrica~ion costs. Also, the lower heat loss reduces
io heating of adjacent electronic components w~ich may be
employed in an attached ballast assembly. ~fficiency is
- also ~mproved over conventional fluorescent l~mps because
the energy lost in conver~ing a 326 nanome~er light qu~tum
to a 555 nan~meter visible light quantum is only 1.2 electron
lS vol~s as compared to the 2,1 eleetron volt loss incurred in
converting 254 nanometer wavelengths to visible radia~ion,
Whlle theconcept of employing longer wavelength ul~raviole~
rad~a~ion sources to reduce quantum lo~s ha3 been proposed
be~ore, i~ has also been shown that the propo~ed use of
cadmium to effect this reduction actu~lly results in no
impro~ment in efficiency because long waYele~gth ult~aviolet
is only a small part of the radiated output for cadmium,
See the article titled '~ow-Pressure High-Current Cadmium
Vapor Discharge in the Middle Ultraviolet" in Yolume 49,
page 553 of the Journal o~ Applied Physics ~1978), by
Peter D. J~hnson.
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In the present invention, since the required
vapor pressure of copper halide is easy to attain and ~he
arc is based on a single radia~ing component system, ~he
output of the lamp is independent of operating position.
~5 Furthermore, copper halides are che~ically ~able and do
not react with arc tube components. Additionally, they are
non-h~groscopic which simplifies l~mp fabrication. A further
improvement ~co be noted in the copper fluorescent arc lamp
is ~he fact ~hat the pho~phor is isolated rom the discharge.
10 As opposed to conventional fluorescent lamp~, the
environment of the phosphor, vacuu~ and inert ga~ can be
selected independently thereby eli~ nating phosphor de~eriora-
tion due to the presence of mercury atoms or ions, electron~,
or very short wavele~gth ultrav~olet radi~tion,
From the abo~e it may be apprecia~ed that ~he
lamp of the presen~ invention provides a unique and no~el
l~mp whic~ acts as an efficient, long lived replacemen~ for
the conventional incandes ent lamp. ~oreover, t~rough the
add~-t~-on of varying amo~nts of mercury wi~hin the arc ~u~e,
a whole range of lamps may be fabrica~ed in accordance`with
~he present inven~ion.
. While the invention has been described in detail
herein, in accordance with cer~ain preferred embodime~ts
thereof, many modifications and changes therein may ~e
effected by those ~killed în the art, Accordingly, it is
intended by the appended claims to cover a~l such modifications
and change~ as fall withi~ the true spirit of the in~en~ion.
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