Note: Descriptions are shown in the official language in which they were submitted.
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Title: BIASING SYSTEM FOR REDUCING ION LOSS
IN LAMPS
SPECIFICATION
This invention relates to luminaire and ballast
circuit techniques for minimizing the loss of plasma
chemicals and ions from the confining arc tube of an
energized plasma in a high intensity discharge lamp.
Back~round of the Inve~tion
It has been recogniæed for many years that sodium
ions in high pressure sodium ~HPS) lamps, as well as
ions of other elements in other lamp types, are lost by
the migration of those ions through the walls of the
arc-containing media in which the ionized gases are
confined under electrically energized and operating
conditions. The basic problem has been discussed in
texts as well as some prior patents. Metals, such as
sodium, which are placed within t~e lamps and are
evaporated and driven into a gas discharge are
essential for the creation and maintenance o~ an
ionized plasma conductor wh~ch creates the light output
produced by the lamp. Each type of lamp is produced
with a fill or starting gas, with certain amounts of
metals, halide and amalgam, and frequently with a
mixture of elem nts, each to be operated at a selected
partial vapor pressure magnitude, so that the light
- output will have the desired color spectrum and lumen
output level when it is appropriately electrically
energized. Clearly, when plasma materials escape from
the discharge lamp as a result of the ion loss, the
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characteristics of the lamp deteriorate with color
shifts and fall-off of lumen output level and are no
longer in accordance with the design and operating
characteristics desired. In addition, the useful life
of the lamp is shortened considerably because of the
drops in lamp performance and because the lamp
operating voltage ri6es which results in undesired
electrical operating changes.
While certain proposals have been advanced to
mitigate this loss, a practical, effective and
economical solution to the problem has not been found.
Sodium loss is one of the major causes of high
intensity discharge performance fall-off with operating
time.
SummarY of the Invention
An ob~ect of the present invention i6 to provide
an electrical system to reduce the loss of gas ions
from lamp structures in a luminaire.
A further object is to provide a circuit which is
simple and inexpensive, which operates effectively and
which, in conjunction with the ballast and fixture, can
be provided for lamps and ballasts o~ a wide variety of
types and sizes.
Briefly described, the invention comprises an
electrical system for inhibiting ion loss from a plasma
conductor in a high intensity discharge lamp. The lamp
includes an arc tube chamber for containing an
ionizable fill gas and plasma materials including a
metal halide which when evaporated and in discharge
; 30 contribute to the formation of a plasma conductor, the
arc tube chamber having electrical terminals. First
circuit means including a ballast provides AC operating
voltage to the terminals of the arc tube chamber. An
electrically conductive surface substantially surrounds
and encloses the arc tube chamber. Second circuit
means is connected to a voltage ~ource for developing a
DC potential, the second circuit means having positive
and negative output terminals. Third circuit means
connects one of the DC output terminals to one or both
of the electrical terminals of the arc tube. The other
of the DC output terminals is connected to the
conductive surface enclosing the arc tube to establish
an electric field between the surface and the arc tube
thereby to confine in the chamber those ions having the
same polarity as the surface.
Preferably, the electrically conductive surface
includes a reflector normall~v used physically close to
the lamp and, in a fixture having a transparent light
window surface near the lamp but on the opposite side
thereof from the reflector, a second conductive surface
comprising a substantially transparent thin film on the
glass or plastic window can be provided to establish a
lamp-enclosing elec~ric bias voltage field. Other
conductive parts of the fixture housing can also be
used as bias-producing conductive surfaces but the
physically close reflector has the greatest impact.
Some luminaires hava a primary reflector placed in
front of the lamp and a larger secondary reflector
placed behind the lamp. Each of these reflectors can
provide bias surfaces.
Brief Description of the Drawlnq_
In order to impart full understanding of the
manner in which these and other objects are attained in
accordance with the invention, particularly
advantageous embodiments thereof will be described with
reference to the accompanying drawings, which form a
part of this specification, and wherein:
Fig. 1 is a schematic diagram of a luminaire
including a plasma conductor chamber therein
illustrating the principle of the invention;
Fig. 2 is a diagram of the bias voltage fields
produced in a typical luminaire structure in accordance
with the invention;
Fiq. 3 is a schematic diagram of a first
embodlment of a luminaire including a system in
accordance with the invention;
Fig. 4 is a schematic diagram of a further
embodiment of a luminaire incorporating the system of
the present invention;
Fig. 5 is a schematic circuit diagram of another
embodiment of a luminaire incorporating a system in
accordance with the invention;
Fig. 6 is a schematic side elevation, in partial
section, of a portion of a luminaire having primary and
secondary reflectors usable in conjunction with the
present invention; and
Fig. 7 is a schematic diagram of the application
of the invention to a large number of lighting ~ixtures
in a building~ as shown with Fig . 5 .
Description of the Preferred Embodiments
Fig. 1 illustrates, in a simplified form, the
interconnection of major components of the apparatus in
accordance with the invention. The invention will be
described in the context of a luminaire having a high
pressure sodium or metal halide light source therein.
It should be emphasized, however, that a variety of
types of lighting fixtures can benefit from the
invention and that a variety of other types of
discharge lamps using gases other than sodium are
usable with the invention.
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The luminaire of Fig. 1 has a housing,
schematically indicated at 10, having a transparent
portion 12 which can be a refractor or an openable
access door typically having a glass panel therein.
The light source itself includes a plasma conductor 14
formed within a chamber such a~ ~n arc tube 16 which
contains an ionizable gas and which can be 6urrounded
by an outer jacket or envelope 17. The lamp may,
however, not have an outer jacket as is the case with
many double-ended lamps. The shapes and sizes of these
components are variable with the type of lamp and the
manufacturer. A reflector 18 is schematically
illustrated as being on the opposite side of the light
source from the door or refr~ctor 12 and, as is
commonly the case, can be curved to direct light from a
portion of the source to create a particular light
output pattern as well as to enclose the light source.
A supply circuit has terminals 22 which are
connectable to a standard AC source of voltage. Supply
circuit 20 provides an AC output on conductors 24 and
25 which are connected to the lamp terminals at
opposite ends of chamber 14. A DC circuit 28 is
conveniently powered ~rom the supply circuit 20 and
produces a DC potential at output terminals 30 and 31
which are positive and negative, respectively. In the
embodiment shown, which involves a ~odium vapor plasma
conductor 14 in chamber 16, the posltive terminal of DC
circuit i8 is connected to reflector 18 and negative
terminal 31 is connected to the arc tube at one end of
the plasma conductor.
In the operation of the ~imple circuit of Fig. 1,
the AC supply circuit 20 provides AC operating current
on lines 24 and 25 into the ends of arc tube chamber 16
to the plasma conduct~r ln chamber 16, maintaining the
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plasma in a condition to create light which passes
through door or refractor 12. The light is directed or
focused by reflector 18. At the same time, DC
potentials are placed on the reflector and the plasma
conductor causing the reflector to be positive with
respect to the plasma. Because the plasma contains
sodium ions which have ~ositive charges, a positive
potential with respect to the plasma conductor is
placed on reflPctor 18, causing an electric field
lo between the re~lector and the plasma ions which tends
to repel the positively charged plasma particles away
from the reflector and which thereby helps confine
those particles within chamber 16. This electric field
significantiy reduces the amount of migration of these
positive ions through the walls of arc tube 16,
lengthening the life of the tube and maintaining ths
sodium design balance, thus improving the color and
light output thereof for an extended interval of time.
The operation of the apparatus of Fig. 1 is
improved by adding an electrically conductive coating
34 to a surface of door or refractor 12 and connecting
positive terminal 30 to coating 34. The result of this
arrangement is to completely enclose the plasma in a
repelling electric field from all sides of the light
source, enhancing thP confinement of ions within the
plasma body and ~urther improving and lengthening the
operation thereof.
Fig. 1 also shows the connection 35 of the
positive termlnal of the DC source to fixture housing
10. The housing is made partly or entirely o~ metal
or, if not, can be made partially electrically
conductive by the addition o~ a conductive film or
filler. By connection 35 to this conductive region,
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the entire housing lo can be used to enhance the field
which aids in confinement of the ions in chamber 16.
of particular importance ls the provision of a
surface or surfaces substantially surrounding and
enclosing the lamp and the development on those
surfaces of a potential which repels and confines ions
in the arc tube chamber. This is accomplished without
adding devices inside of the structure of the lamp
itself which is an expensive and undesirable approach.
It will be apparent that when extra devices are
included in the lamp outer jacket, they are necessarily
thrown away with the lamp when its useful life has
ended, but circuitry added to the luminaire structure
remains and is effective to lengthen the life of every
lamp installed therein.
Fig. 2 schematically illustrates the relationship
between a light source 38, a reflector 39, a refractor
40 and an enclosing housing 41 where the reflector is
metal or has a metallized surface and the refractor 40
also has a metallized surface, both of these components
and the conductive.housing 41 being connected to the
positive terminal of DC ~ource 28 while the negative
terminal thereof is connected to the plasma conductor
light source. Again, assuming a sodium vapor lamp, a
three-dimensional field 42 is produced between the
plasma conductor and the surroundi,ng ~hell-like bodies
which is extremely effective in confining the plasma
components within their containing chamber. Because
the bodies themselves substantially surround or enclose
the light source, the confining effect is considerable.
~he geometric relationship illustrated is commonly
arranged as shown in Fig. 2 for optical reasons but has
not been employed for electric field reasons or for the
confinement of ions in a plasma stream heretofore.
The application of this principle to one form of
luminaire is shown in Fig~ 3 wherein the components of
the luminaire are largely contained within a housing
44. Housing 44 is either metal, filled with metal
particles or is coated with a metallized surface. The
housing includes an opening which receives a glass or
plastic refractor 46 having a conductive coating 48 on
the inner surface thereof. Coating 48 can be, for
example, a thin layer of tin oxide or indium oxide
which leaves the refractor substantially transparent
but which renders the inner surface thereof
electrically conductive. Such a layer can be placed on
glass by conventional deposition techniques.
Behind the refractor 46 is a plasma chamber 16
surrounded by an outer ~acket 17 and behind this light
source is a reflector 18.
An AC supply circuit indicated generally at 20
includes a conventional metal halide lamp ballast
indicated at 50, the ~allast typically being a constant
wattage auto-transformer or peak lead autoregulator
with the tap and common points arranged for connection
to an AC source. The usual ~ingle ballast capacitor,
which would be connected in series between the ballast
transformer and the plasma chamber, i~ replaced by two
ballast capacitor~ 52 and 53 which are connected in
series with the two AC lines leading from the ballast
transformer to the light source. In order for the lamp
operating wattage to be correct, each of capacitors 52
and 53 is selected to have a value of twice the
capacitance of the single series capacitor which would
normally be used with the ballast transformer. These
capacitors provide isolation for the light source so
that a DC bias can be placed thereon.
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A voltage divider means includes a potentiometer
54 connected across the output of transformer 50 with
the movable contact 55 being connected to the DC
circuit means 28. Contact 55 is connected through a
series resistor 56 and diode 58 to the parallel
connection of a capacitor 60 and a resistor 61. The
other side of the parallel circuit is connected to the
common line which is also connected to conductive
housing 44 at a screw terminal 62.
lo The positive output terminal of this DC circuit,
which is the common line, is also connected to
reflector 18 and conductive coating 48 on the
refractor. The negative side is connected to the
movable contact 59 of a potentiomet~r 57. The ands of
the potentiometer are connected to the terminals of the
plasma conductor chamber. The resulting field tends to
confine positive ions in chamber 16, inhibiting
migration thereof through the walls of the chamber.
Because the positive terminal is connected to the
housing at terminal 62, the housing itself, which is
made of conductive material, can participate in
creation of the confining field.
As previously indicated, this apparatus as
illustrated in Fig. 3 can be used without coating 48,
relying upon the field produced by physically close
reflector 18 and the housing. As suggested by Fig. 2,
reflector 18 can be formed as a shell-like structure to
more fully enclose the chamber and improve the effect
of the confining field.
It should also be noted that the reversal of diode
58 causes reversal of the DC field so that either
positive or negative ions can be confined using
essentially the same circuit, the choice being made on
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the basis of the type of lamp and the ions or chemicals
used therein.
A circuit which uses an electromagnetic regulator
i6 illustrates in Fig. 4. Many of the components
including the housing, refractor, reflector and light
source are the same as in Fig. 3 and are similarly
numbered. The AC supply circuit indicated generally at
64 includes a magnetic regulator having a core 66 with
three windings all of which are electrically insulated
from the core and from each other. An isolated primary
winding 68 is connectable to a conventional AC source.
An output winding 70 is connected at its ends to
chamber 14 and is tapped for connection to a starting
circuit 72. Starting circuit 72 can be any of a
variety of starting circuits which are now conventional
in this art, using a discharge circuit to provide
voltage pulses across the smaller, upper portion of
winding 70 which is magnified by the auto transformer
effect in winding 70 to provide a relatively high
voltage pulses across conductors 74 and 75 for
application to the deionized lamp to effect ignition.
A suitable starting circuit is shown, for example, in
Fig. 2 and other figures of U.S. patent 4,763,044,
Nuckolls et al. Magnetic shunts 65 and 67 extend
across windings 68 and 70.
A separate floating ballast capacitor winding 76
is provided with a shunt capacitor 78 which performs
the ballast capacitor function. This separate ballast
winding does not interfere with the electrical
isolation ~f the primary winding and does not interfere
with the normal AC operation of the ballast-lamp
system. Winding 70 is connected through a diode 80 to
; a capacitor 82 across which the DC bias voltage appears
for connPction to the light system components. A
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bleeder resistor ~3 is connected in parallel with
capacitor 82. In the embodiment shown, intended for
use with a sodium vapor lamp, the negative terminal of
this DC supply is connected to common line 75 and to
the plasma conductor chamber 16. The positive terminal
is connected to reflector 18, conductive coating 48 and
the conductive housing 44. The function is the same as
in connection with the other embodiments discussed
above in which a field is produced between the
reflector, the refractor and the plasma conductor
chamber to confine gasas and ions therein.
These biasing techniques permit lamp design
changes such as increased arc tube wall loading (watts
per square cm.) with quartz and polycrystalline alumina
to generate higher lumen-per~watt (L.P.W.) output and
better color and other characteristics without the
normal increase in the rate of sodium loss from the
plasma and arc tube.
Fig. 5 shows a still further embodiment of a
plasma-combining circuit apparatus in accordance with
the invention which is particularly simple and
therefore economically advantageous as well as being
effective. In a manner similar to the embodiment of
Fig. 3, an auto-transformer 92 i5 connected to a AC
source and 5uppl ies AC current to a lamp indicated
generally at 94 through series capacitors 96 and 97. A
lamp starting circuit ~8 is connected between the lamp
sides of capacitors 96 and 97. A reflector 99 is
positioned to reflect the light produced within lamp
94.
A DC circuit indicated generally at 100 includes
the series connection of a diode 102 and a resistor 104
with the addition of a radio frequency choke 106 which
is included to block high ~requency, high voltage
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pulses from the lamp starting circuit. The diode is
polarized so that the inductive ballast side of
capacitor 97 is positive relative to the lamp side of
the capacitor, and the polarization o~ capacitor 96 is
also such that the inductive ballast side of the
capacitor is positive with respect to the lamp side.
Capacitor 96 is dielectrically insulated from the
housing of the fixture. Finally, a conductor 108
interconnects the neutral or ground side of the line at
lo inductor 92 to the reflector and also to the lamp
housing 90.
With this circuit, the neutral side of the
inductive ballast i8 positive with respect to the lamp
as well as the lamp circuitry on the lamp side of
capacitors 96 and 97. Thus, the plasma conductor
itself is negative with respect to the reflector and
the housing, again producing the ion migration-inhibit-
ing field which improves lamp operation and lengthens
life. Electrical isolation of capacitor 96 from the
fixture housing by dielectric insulation prevents the
high frequency, high voltage lamp ignition pulses from
circuit 98 ~rom being capacitively shorted out. The
ballast secondary coil serves as an inductancP which
holds off the starting pulses from the starter circuit.
The charging network comprising diode 102, resistance
104 and the choke charges the ballast capacitor 36 with
the polarity shown. When the lamp strikes and draws
high AC lamp current, part of the charge on capacitor
96 is conducted to ballast capacitor 97 until their DC
voltages are equal and opposite so that the net DC
voltage around the lamp power loop is zero. However,
the lamp plasma circuit is biased negatively with
respect to the neutral or metal parts.
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The AC voltage swings across the operating lamp in
this circuit are allowed to have a peak amplitude
approaching or nearly equal to the DC biased voltage.
Thus, there exists very little if any voltage time in a
half cycle in which a reverse-bias exists and which
would tend to drive sodium ions through the walls of
the arc tube.
The DC voltage is self-adjusting by the lamp
voltage clamping mechanism in this circuit. Note that
lo two of these charging networks loo could be used, but
it is not necessary because the AC power operation
carries the re~uired charge from one capacitor to the
other.
Resistor 104, typically having a value of 10 K
ohms, 1 watt, is used to limit the charging circuit
current. As previously indicated, the RF choke tends
to block the high voltage from the starter, allowing
the high frequency, high voltage to raise and ignite
the lamp and also keeping the high voltage from
damaging other charging circuit components. The diode,
of course, allows the half-wave DC charging to take
place.
If discharging of the ballast and starter capac-
itors are required when the ballast is deenergized,
high resistance bleeder resistors can be connected
across those capacitors. Rapid discharging, if
desired, can be accomplished by connecting a small
relay having individual normally closed contacts series
connected with a small resistor across each capacitor,
the relay coil being connected across the line or the
ballast secondary.
Fig. 6 shows a reflector arrangement which can be
used in conjunction with the present invention to
considerable advantage. In some fixtures, the lamp 110
is positioned between a primary reflector and a
secondary reflector 112. The two reflectors are used
to project light from the lamp through refractor or
cover 113 in a particular pattern. As before, these
components are mounted in a housing 114.
By connecting one side of the DC supply to both
reflectors and the other side of the supply to one or
both terminals of the lamp, the reflectors form an
enclosing field which is highly effective because the
reflectors substantially enclose the lamp and are
physically closer to the lamp than the remainder of the
housing. Any of the circuit arrangements discussed
herein can be applied to this reflector arrangement.
~he invention has thus far been described in the
context of a single lighting fixture or luminaire.
However, it is quite possible to apply the invention to
all lighting fixtures of a similar type in an entire
building. As will be recognized, this has advantages
of economy. A technique ~or doing this is
schematically illustrated in Fig. 7 wherein a building
120 has a large number of lighting fixtures, two of
which are illustrated at 122 and 123. Each fixture
typically has a ballast transformer 125 and a ballast
capacitor 126 which can be arrangad in a manner similar
to the circuits illustrated in Figs. 3 and 4 but need
not be. Each fixture also has a lamp 127, such as a
sodium vapor lamp, and a reflector 128. Starting
circuit means can also be provided in or associated
with the ballast circuitry.
The primary winding of an AC power and DC
isolation transformer 130 is connected to the
~onventional AC lines feeding the building. ~he
fixtures 122, 123, ... are connected in parallel across
~he high and common terminals of the transformex
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secondary windlng. In the particular embodiment of the
fixtures shown, the primary portion of each fixture
ballast transformer is connected thus to the AC supply.
A DC supply unit 132 is connected between the AC
common line from the secondary of transformer 130 and
building ground, i.e., the green wire in a three-wire
electrical system, with the positive output terminal of
the DC source being connected to building ground. This
establishes a DC bias between the common line and
building ground with ground being positive relative to
the common line. In order to provide the desired bias
to confine the material in the lamp in accordance with
the invention, it i5 only necessary to connect the
reflector and/or the housing of each fixture (depending
upon the specific reflector and housing structures) to
building ground. Since the plasma conductor is
connected to the common AC line, it is automatically
biased negative relatlve to ground. The reflector
and/or housing is thus made positive relative to the
plasma, creating the desired confining field. It is
necessary to be sure that all wiring used for fixtures
in this fashion are connected to the isolation
transformer 130 if other AC supply cables are employed
~; for other purposed in the building. A dedicated cable
for this DC biasing is preferred.
While certain advantageous embodiments have been
chosen to illustrate the invention, it will be
understood by those skilled in the art that various
changes and modifications can be made therein without
departing from the scope of the invention as defined in
the appended claims.
