Note: Descriptions are shown in the official language in which they were submitted.
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High Pressure Arc Lamp With Internal Reflector and Applications Therefor
' Background of the Invention
. This invention relates to an arc lamp containing an inert gas pressurized to
several or more atmospheres. More particularly, this invention relates to a
high pressure,
short arc discharge lamp with an internal reflector and compact design to
provide a high
power point source of light. The lamp utilizes an inert gas such as argon or
xenon gas and
can operate at tens to thousands of watts. The invention further relates to
applications for
such a lamp, including curing of photocurable materials, and tooth whitening
procedures.
Arc lamps, particularly short arc xenon lamps, are known in the art for
various
applications, such as infrared and visual searchlights, fiber optic
illumination, spectroscopy,
stadium lighting, stage and screen lighting, automobile headlights, and
microscopy. The
spectral distribution of xenon lamps is similar to that of natural daylight.
In addition, short arc xenon lamps with internal reflectors are known in the
art.
The use of internal reflectors allows for compact designs. For example, U.S.
Patent No.
4,633,128 to Roberts et al. generally describes the typical construction of a
short arc lamp
with an internal reflector. Such lamps include a sealed, concave chamber with
a gas such as
xenon pressurized to several atmospheres at ambient conditions. An anode and a
cathode are
mounted along the central axis of the chamber and define the arc gap. An
integral concave
reflector serves to collimate light generated at the arc gap and a window,
typically made of
sapphire, permits external transmission of the collimated light.
In order to electrically isolate the two electrodes, existing short arc lamps
use a
ceramic body, typically made from a ceramic alumina material, from which the
concave inner
surface is formed. Metal bands are used at the base and window ends of the
ceramic body to
provide an electrical conductor for the electrodes and mount the window
assembly,
respectively. Roberts et al. illustrates this type of configuration for an arc
lamp. The internal
surface of the ceramic, which may be parabolic, elliptical, or aspherical in
shape, is provided
with a deposited reflective metal coating. As is recognized by Roberts et al.,
problems arise
. when these prior art arc lamps are used at high power levels. Temperatures
within the lamp
can exceed 20~° C, thus causing substantial temperature gradients
through the lamp body.
This can cause cracking of the reflector surface or ceramic body when the lamp
is operated at
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high wattages, i.e., exceeding 800 watts. Such cracking can cause
discontinuations or
discolorations in the reflective surface of the lamp, thereby diminishing its
effectiveness.
Moreover, cracks can lead to an explosion of the lamp.
U.S. Patent No. 3,715,613 discusses the limitations of arc lamps using ceramic
bodies when operated at high pressures. These include the limited tensile
strength of ceramic,
the limited strength of the brazed joints between the ceramic body and metal
members, and the
problems associated with cooling the lamp due to the relatively low thermal
conductivity of the
ceramic.
The use of light, and in particular light in the blue spectrum, is beneficial
in
tooth whitening procedures because light in this wavelength tends to be more
readily absorbed
by yellow/brown colored stain molecules but mostly reflected by the red
colored tooth pulp in
vital teeth. One such tooth whitening procedure utilizes a whitening agent,
such as a peroxide
compound, in combination with laser light from an argon laser to generate free
oxygen
radicals to accelerate the whitening process. Such procedures, however, can
require a lengthy
office visit due to the amount of time each tooth must be exposed to laser
light in order to
effectuate the whitening process. This is because the argon lasers used in
these procedures
typically have output powers in the range of 250 mW - SOOmW.
The spectral output of an arc lamp may be adjusted by altering the fill
pressure
and thus the gas density within the sealed chamber of such a lamp. In
particular, depending
on the gas or combination of gases used, higher fill pressures for arc lamps
are desirable
because varying the fill pressure causes slight but desirable shifts in the
spectral output of the
lamp. Such shifts are significant in that they provide for additional power in
desired
wavelengths and thus increase the efficiency of the lamp. For example, an
increase in
pressure of argon in an arc lamp results in a shift in spectral output that
increases the amount
of blue light generated. Blue light is desirable because it is useful both for
curing
photocurable resins and composites and in tooth whitening procedures. Thus, it
is possible to
increase the efficiency of an arc lamp by increasing the fill pressure to
obtain the same output
level in the blue spectrum with less input power.
However, prior art arc lamps are unable to accommodate fill pressures much
above 50 psig due to their construction using a ceramic body. And the use of
argon in a short
arc lamp at SO psig is not practical because at this pressure, the power
output in the visible
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spectrum is insufficient to create an efficient system for curing and
whitening applications. At
50 psig, xenon gas .is more efficient for providing visible output. Thus,
prior art arc lamps
utilize xenon gas due to the limitations of the design of these lamps.
Applicant has found,
however, that due to the shifts in spectral output achieved, the use of argon
gas at a fill
pressure of 200 psig significantly increases the efficiency of an argon arc
lamp system beyond
that of a short arc xenon lamp with a 50 psig fill in terms of visible output.
Moreover, argon
gas is significantly less costly than xenon gas. Thus, there is a need for a
compact arc lamp
design that can safely withstand fill pressures of at least 200 psig.
Prior art arc lamps have attempted to address this problem with complicated
mufti-part designs that attempt to place ceramic insulators in compression
rather than tension.
For example, U.S. Patent No. 4,179,037 discloses a ceramic ring separating a
cathode ring
and an anode ring. Kovar sealing rings separate the ceramic ring from the
anode and cathode
rings. This design, however, is complicated due to the two piece housing and
ceramic sealing
ring structure, and thus costly to manufacture. In addition) although the
ceramic ring is
stronger in compression than tension, it is still the weak point of the
structure and thus limits
the pressure of the gas that may be used within the arc lamp.
U.S. Patent No. 3,715,613 discloses a high pressure arc lamp with an all metal
enclosure which comprises the cathode and a ceramic insert to isolate the
anode from the
cathode. The ceramic insert is brazed to the interior of a portion of the
metal enclosure. The
design is intended to place the ceramic in compression as opposed to tension
as ceramic is
much stronger in compression as opposed to tension. This design, however, is
complicated
and difficult to manufacture because the portion of the metal housing that
encases the ceramic
insert must have a coefficient of thermal expansion that closely matches that
of the ceramic.
Thus, the housing is made from two separate materials that are joined
together. In addition,
like prior art designs using a ceramic body for the lamp, the ceramic insert
is in the heat
transfer path and thus presents problems in dissipating heat due to its
relatively low heat
transfer properties. Thus, specially designed heat transfer members are
rewired to transfer
heat from the ceramic to the metal enclosure. In addition, this design is not
readily
refurbishable.
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There is thus a need for a compact, high pressure arc lamp with an internal
reflector that is economical and easy to manufacture and does not suffer from
the drawbacks
of prior art arc lamps.
For both composite and resin curing as well as tooth whitening procedures,
higher power light sources are desirable to both reduce the time for
completing the procedure
and improve the results thereof. For example, for both these applications, the
energy
requirements are determined in accordance with a total amount of energy to be
imparted to a
given tooth. Typically, 20 joules of total energy per tooth is the maximum
energy provided
for both curing and tooth whitening applications. This figure is used to
ensure that the pulp in
vital teeth is not damaged. Existing curing lamps and lasers used for curing
and whitening
procedures generally operate at power levels of less than 1 watt. Thus, it
takes in the range of
20-60 seconds to impart the required amount of energy to a tooth. Due to the
problem of heat
dissipation, however, power levels in arc lamps using a ceramic body are
limited because of
the relatively poor thermal properties of ceramic and the greatly reduced
strength of ceramic
at elevated temperatures.
As discussed above) it is desirable to use elevated fill pressures to achieve
these
power outputs with greater efficiency. In particular, an arc lamp that can
operate at fill
pressures of 200 psig is particularly desirable because of the significant
increase in efficiency
made possible by the resulting shift in spectral output.
Improved results are obtained during curing because photocurable composites
and resins typically exhibit improved properties the faster they are cured.
Similarly, with
regard to whitening procedures using peroxide compounds, the bleaching
efficiency of the
peroxide is improved because as more energy is applied, more of the peroxide
is broken down
into free oxygen radicals. The longer the peroxide is resident on a tooth, the
greater the
amount of molecular oxygen produced, which does not have nearly the same
bleaching effect
as free oxygen radicals.
Summar~r of the Invention
In accordance with the present invention, a high pressure arc lamp with an
internal reflector is disclosed. The housing of the lamp is formed entirely
from metal and is
maintained at the same potential. A concave metal, glass, or ceramic reflector
defining a
curved reflecting wall is fitted within the housing symmetrical about a
central axis of the
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lamp. A circular window is mounted within the metal wall opposite the
reflector and
symmetrical about the axis of the lamp to pass focused light. The cathode is
suspended within
' the housing and enters through this same metal wall opposite the reflector.
The cathode is
isolated from the anode by a dielectric material disposed between the cathode
and the metal
5 wall. With the design of the present invention, internal gas fill pressures
of 200 psig (at
ambient conditions) are possible in a compact design. In addition, because of
the all metal
housing, the lamp may be operated at powers of up to 3000 W and more as the
heat generated
by the lamp is efficiently transferred through the end of the lamp opposite
the window.
The present invention also encompasses a method of curing photocurable
materials using a high pressure arc lamp with an all-metal housing and
internal reflector. The .
method includes providing a light guide to direct the output of a lamp of the
present invention
to a material to be cured and energizing the lamp for a sufficient amount of
time to cure the
material. The present invention further encompasses a method of whitening
teeth using a high
pressure arc lamp with an all-metal housing and internal reflector. The method
includes
treating a tooth to be whitened with photoactivated bleaching composition, and
providing a
light guide to direct the output of a lamp of the present invention to the
tooth and energizing
the lamp for a sufficient amount of time to cure the material.
The present invention also includes a method of curing photocurable materials
using a compact argon arc lamp with an internal reflector. The method includes
providing a
light guide to direct the output of a lamp of the present invention to a
material to be cured and
energizing the lamp for a sufficient amount of time to cure the material. The
present
invention further includes a method of whitening teeth using a compact argon
arc lamp with an
internal reflector. The method includes treating a tooth to be whitened with
photoactivated
bleaching composition, and providing a light guide to direct the output of a
lamp of the
present invention to the tooth and energizing the lamp for a sufficient amount
of time to cure
the material.
An advantage of the present invention is that a compact, short arc lamp with
an
internal reflector is provided that may be operated at high pressures and
power levels. With
the design of the present invention, input powers of over 1500 watts for
continuous operation
are possible.
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An additional advantage of the present invention is that a high pressure arc
lamp
is provided in an envelope comparable to that of prior art arc lamp systems,
thereby allowing
for shifting of the spectral output of the lamp to improve its efficiency.
A further advantage of the present invention is that a compact arc lamp with
an
internal reflector is provided that is capable of safely operating at
significantly greater pressure
levels than prior art arc lamps.
A further advantage of the present invention is that a compact arc lamp with
an
internal reflector is provided that is capable of operating at significantly
greater power levels
than prior art arc lamps.
An additional advantage of the present invention is that it provides improved
methods of both curing resins and composites and tooth whitening using a high
pressure arc
lamp with an internal reflector.
An additional advantage of the present invention is that it provides improved
methods of both curing resins and composites and tooth whitening using an
argon arc lamp
with an internal reflector.
An additional advantage of the present invention is that it provides for a an
arc
lamp design that is relatively simple to manufacture and can be refurbished by
the replacement
of parts that have degraded.
Brief Description of the Drawings
The foregoing summary, as well as the following detailed description of a
preferred embodiment, is better understood when read in conjunction with the
drawings
appended hereto. For purposes of illustrating the invention, there is shown in
the drawings a
presently preferred embodiment, it being understood, however, that the
invention is not
limited to the specific instrumentalities and components disclosed herein.
Fig. 1 is an isometric view of an embodiment of the high pressure arc lamp of
the present invention.
Fig. 2 is a cross-sectional view of an embodiment of the high pressure arc
lamp
of the present invention, taken along the centerline of the lamp.
Fig. 3 is a detailed view of the cathode assembly of one embodiment of the arc
lamp of the present invention.
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Fig. 4 is a detailed view of the anode assembly of one embodiment of the arc
lamp of the present, invention.
' Fig. 5 is a cross-sectional view of a water-cooled embodiment of the high
pressure arc lamp of the present invention, taken along the centerline of the
lamp.
Fig. 6 is detailed view of the window assembly of one embodiment of the
present invention.
Fig. 7 is a cross-sectional view of an embodiment of the high pressure arc
lamp
of the present invention including an adapter for mating with a fiber optic
connector.
Fig. 8 is the diagram for the spectral output of a filter that may be used in
conjunction with the arc lamp of the present invention for curing and tooth
whitening
applications.
Detailed Description of the Invention
The present invention comprises a high pressure) arc lamp with an all metal
enclosure and an internal reflector. The lamp housing of the lamp is formed
entirely from
metal and is maintained at the same potential. A concave metal reflector
defining a curved
reflecting wall is fitted within the housing symmetrical about a central axis
of the lamp. A
circular window is mounted within the metal wall opposite the reflector and
symmetrical about
the axis of the lamp to pass focused light. The cathode is suspended within
the housing and
enters through this same metal wall opposite the reflector. The cathode is
isolated from the
anode by a dielectric material disposed between the cathode and the metal
wall. With the
design of the present invention, a gas fill pressure of 200 psig is possible
in a compact design.
In addition, because of the all metal housing, the lamp may be operated at
powers of up to
3000 W and more as the heat generated by the lamp may be efficiently
transferred through
end of the lamp opposite the window.
The metal chosen for the housing should be high in strength, have high heat
transfer capabilities and be resistant to corrosion. In a preferred
embodiment, stainless steel is
used. The use of an all metal enclosure allows for much higher pressures and
operating
temperatures than is possible with prior art lamps that utilize ceramic
bodies. The use of a
metal enclosure also makes the lamp more durable and refurbishable and allows
for much
more efficient air and/or water cooling as compared with ceramic bodies.
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Fig. 1 is an isometric view of a preferred embodiment of a lamp housing of the
present invention. The housing 10 is in the shape of a hollow cylinder and is
made from
stainless steel with a wall thickness of about 0.06 in. and outside diameter
of 3.0 inches.
Each end of the cylinder is sealed with a cylindrical steel plate 0.25 in.
thick that is welded to
housing 10. Weld lips 39 are used to weld each of the end plates to the
cylindrical housing.
In the front end plate 15, a round hole, symmetrical with the longitudinal
axis of the housing
is cut through the plate in order to mount a window to permit passage of
light. The window
17 is made from sapphire about 1.0 inches in diameter and 0.090 inches thick.
In addition, a
hole offset from the axis of the lamp is provided to mount a fill spout 20 for
filling the
housing with an inert gas, such as argon or xenon. The fill spout is a length
of standard 0.25
inch copper tubing brazed in a through hole in plate 15, and is sealed off
after filling.
Cathode 22 is mounted to a dielectric ceramic insulator 23 which in turn is
mounted to plate
15. A u-shaped connector 12 is provided on the end of cathode 22 to provide a
mounting
surface an electrical connector. The cathode 22 is electrically isolated from
the plate 15,
which is at the same potential as the anode, by the ceramic insulator 23.
Sealing ring 21 is
used to mount the ceramic insulator 23 to the plate 15. Insulator 23 is a
ceramic cylinder with
a through hole passing through its axis for the cathode 22. The mounting
arrangement for the
cathode assembly is described in more detail in connection with Fig. 3.
Mounting holes 14
are provided in the plate 15 for attaching a fiber optic connector adapter and
a ground
potential wire.
At the opposite end, plate 25 is welded to housing 10 and is also a thickness
of
0.25 in. A through hole is provided in plate 25 symmetrical with the axis of
the lamp to
permit mounting of the anode. Cooling fins 30 may be connected to the exterior
of the plate
to help dissipate heat energy generated by the lamp in operation. Mounting
holes may be
provided in plate 25 to permit the cooling fin assembly to be bolted to the
plate. In addition,
a thermal pad or paste may be used to ensure good thermal contact between the
plate 25 and
cooling fins 30. A small fan may be used to circulate air over the fins if
required due to the
duty cycle of the lamp.
The welded construction of the arc lamp of the present invention allows for
the
plates to be easily removed so that the lamp can be refurbished. For example,
the reflector,
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which will degrade as a result of operating the lamp, can be replaced and the
lamp filled with
fresh gas.
' Fig. 2 is a cross-sectional view of the interior of a lamp of the present
invention, showing many of the same features as Fig. 1. At the base portion of
the lamp 25,
plug 35 is welded in a central through hole of plate 25 with its exterior
surface flush with the
exterior surface of plate 25. Plug 35 comprises a base portion and a portion
that extends into
housing 10. The anode portion of the arc lamp of the present invention is
shown in greater
detail in Fig. 4, discussed below.
The anode 35 protrudes through a hole in the base of ellipsoidal reflector 40.
Reflector 40 is an electroformed optical component comprising a nickel
substrate and an
electrodeposited coating of enhanced aluminum. Other coatings may be used)
such as
rhodium. Rhodium is a precious metal with greater than 70% reflectivity in the
near
ultraviolet through infrared ranges. As will be recognized by those of skill
in the art, the
coating is chosen dependent on the particular application for the lamp and
desired wavelength
of transmitted light. For example, for photocuring resins and composites and
tooth whitening
applications, it is desirable to use a dichroic coating which reflects visible
light but does not
reflect infrared light. Reflectors with various surface coatings are available
from Opti-Forms,
Inc. of Temecula, CA.
As indicated, in a preferred embodiment of the present invention, a 3.0 inch
diameter housing 10 is used, although the all metal design permits the arc
lamp of the present
invention to be easily manufactured in larger or smaller sizes. An advantage
of the use of a
3.0 inch diameter housing as compared with 2.0 inch diameter housings that are
standard in
the art is that the increased gas volume obtained with the larger diameter
design dilutes the
impurities released into the gas by the electrodes. That is, given the same
size electrode, the
density of impurities in the gas is less the greater the gas volume. In this
manner, the life of
the reflector is increased because less of the impurities are deposited on the
reflector surface.
As shown in Fig. 2, reflector 40 is held in place within the cylinder 10 by
mounting the forward facing edge of the reflector against a step 41 provided
in the inner
radius of housing 10. The width of the step is formed to approximately the
same dimension as
the thickness of the reflector at its edge. In order to keep the reflector in
place during
operation of the lamp, the reflector 40 may be held in place through the use
of ring 42 toward
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its base, as shown in Fig. 2. Ring 42 is made from 0.060 inch thick stainless
steel and is
welded or brazed to the interior surface of housing 10. The ring is provided
with 4 through
holes approximately 0.25 inches in diameter to permit the flow of gas through
the reflector.
Ring 42 may also be brazed to the exterior surface of reflector 40, but need
not be. Those of
5 ordinary skill in the art will recognize that other means of holding the
reflector in place may
be used. For example, a spring may be provided with one end mounted to the
base of
reflector 40 and the other to the anode 35. In this manner, as the temperature
and pressure
within the lamp increase during operation, thereby causing expansion of the
housing, the
spring would act to hold the reflector in place against the lip in the wall
10.
10 Alternatively, the reflector can be used as the pressure bearing surface
rather
than the cylindrical housing 10 and plate 25. This would require brazing the
reflector 40 at its
base to the anode 35 and at its edge to the lip of the housing 10. In
addition, it is advisable
to use heat transfer pads at the brazes to ensure good thermal contact between
the reflector 40,
housing 10, and anode 35. The advantage of this design is that due to its
curved surface, the
reflector 40 may utilize thin wall construction and still be able to withstand
operating
pressures. In contrast, using a flat end plate 25 requires a greater thickness
of material to
withstand operating pressures. Thus, a reduced weight design can be achieved
by making the
reflector 40 a pressure bearing component of the lamp.
A metal strip 50, referred to as a "getter," may be secured within the housing
as shown in Fig. 2. The strip SO is approximately 8.0 mm wide and 0.30 mm
thick and is
bent to form an accordion-like cross-section as shown in Fig. 2. The getter is
fabricated from
a base strip of nickel plated iron and a layer of ST 101 alloy which consists
of 84
zirconium and 16 % aluminum by weight. Letters are used to absorb impurities
formed
within the cavity during operation of the lamp generated by, e. g. ,
outgassing of impurities
contained within the lamp components. The getter is spot welded at each end to
the interior of
the housing 10. A suitable getter is the ST 101/CTS/NI/8x6 Db0 getter made by
Saes Letters
S.p.A., an Italian company.
An advantage of the disclosed design is that the ceramic insulator 23 is
subject
only to compressive loads, unlike the ceramic bodies of prior art designs that
are in tension.
In addition, there is no ceramic in the heat transfer path from the anode.
Rather, the design
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of the present invention provides for an all-metal heat transfer path in a
simple design that
significantly increases the power level at which the lamp can operate.
The present invention also includes a novel design for mounting the cathode to
the lamp. As shown in Fig. 3, the cathode 22 is mounted within ceramic plug 23
in order to
insulate it from plate 15, which is at the same potential as the anode. The
cathode may be
made from any suitable metal as will be recognized by those of skill in the
art. In a preferred
embodiment, the cathode 23 is comprised of a nickel rod 0.09 inches in
diameter and is bent
to the shape illustrated in Fig. 2. The circumference of the rod 23 is brazed
to the interior
surface of a through hole provided in the ceramic cylinder 23, which is made
from a ceramic
alumina material. A tungsten electrode 29, terminating in a point as shown in
Fig. 2, is
brazed at the end of the cathode 22. As is known to those of ordinary skill in
the art, the
power level of the lamp may be changed by adjusting the position of the
electrode 29 in the
cathode 22 so as to change the size of the arc gap. At the opposite end of the
cathode 23
external to the lamp, a terminal 31 is provided for applying voltage to the
cathode. A s
IS shown in Fig. 3, a ring 21 with a "z" cross section is used to mount the
ceramic cylinder to
the plate 15. In a preferred embodiment, ring 21 is made from stainless steel
but may be
made from kovar or any other suitable metal. The inner circumference of the
ring is brazed
to the ceramic 23 and the outer circumference is brazed or welded to the plate
15. A step 24
is provided in the outer circumference of the ceramic cylinder 23 to
accommodate the ring 21.
Due to the "z" cross section of the ring 21, a gap 26 exists on the exterior
side of the plate 15
between the plate and the ceramic cylinder 23. Similarly, on the interior side
of the plate 15
a gap 27 exists between the plate and the ceramic cylinder 23. Because the
ring 21 is flexible, the ceramic cylinder 23 may be moved in any direction
transverse to its
axis in order to adjust the position of the cathode 22 relative to the anode
35.
Fig. 4 is a detail drawing of the anode assembly of one embodiment of the
present invention. Anode 35 may be welded or brazed in a through hole provided
in plate 25.
In the embodiment illustrated in Fig. 4, the anode 35 is welded to the plate
25 and a weld lip
39 is provided for this purpose. As shown in Fig. 4, the base portion of anode
35 includes a
Zip 38 around its periphery to make contact with the interior surface of plate
25. The lip
allows for self fixturing of the anode 35 in the plate 25 when the two are
welded together.
Tungsten electrode 45 is brazed to the end of the protruding portion of the
anode 35. In a
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preferred embodiment, the tungsten electrode 45 is first brazed or welded to
the anode 35, and
then the combination is machined to the shape shown in Fig. 4. Copper is the
preferred metal
for the anode 35 because of its heat conducting properties, but other metals
may be used. In
order to allow for gas flow around the reflector, the interior radius of
reflector 40 at its base
is made larger than the radius of the protruding portion of anode 35 in order
to provide an
annular gap 43 between the base of reflector 40 and the anode 35. In addition,
the base of
reflector 40 is spaced from the base portion of anode 35 to allow for thermal
expansion of the
reflector 40 when the arc lamp is in operation.
The design of the anode 35 in conjunction with plate 25 provides for
significantly improved heat transfer as compared with prior art ceramic arc
lamps. Rather
than transferring heat from the anode through a ceramic material as in prior
art designs, the
heat is transferred directly through a highly thermally conductive material
such as copper. As
shown in Fig. 2, the anode 35 may be thermally coupled to cooling fins 30 to
facilitate heat
removal.
Fig. 5 illustrates an alternate embodiment of the present invention intended
for
high duty cycle operations and power levels greater than 1600 watts. The
design of the
present invention provides for much improved water cooling capabilities than
existing designs.
As shown in Fig. 5, a water (or other coolant) supply tube 36 may be made
integral with
anode 35 so as to provide cooling water to the rear surface of tungsten
filament 45. In this
embodiment, to facilitate welding of the anode 35 to the plate 25, the weld is
placed in the
internal side of the plate 25. In this case, a lip is provided on the external
side of anode 35 to
provide for self fixturing during welding. Due to the design of the arc lamp
of the present
invention, a very short thermal path for heat generated by the lamp is
provided to permit
continuous operation at high power levels. A return tube 37 is welded or
brazed to tube 36 to
provide a return path for the cooling water.
Fig. 6 illustrates a detail of the sapphire window assembly. Window 17 is
brazed along its periphery to kovar ring 18, which is welded or brazed to the
plate 15 along
its outer circumference. In the embodiment shown in Fig. 6, the kovar ring 18
is welded to
the plate 15 and a weld lip 39 is provided for this purpose. As shown in Fig.
2, a lip 19 is
provided in the kovar ring 18 along the interior surface to provide a surface
upon which the
window 17 bears. This helps to minimize the risk that the window can be forced
from the
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enclosure due to the internal pressure. An annular gap 13 is provided between
the plate 15
and the kovar ring 18 to allow for thermal expansion of the window assembly
during operation
of the lamp.
Fig. 7 illustrates the arc lamp of the present invention provided with a fiber
optic connector 70 mounted to the exterior of plate 15. In a preferred
embodiment of the
present invention, the body of the lamp, including the housing 10 and end
plates 15 and 25,
are maintained at ground potential. This allows for the mounting of metal
components to, and
easy handling of, the lamp. The coupling may thus be made from stainless steel
or another
metal and is provided with an internal conical portion 72 that tapers to a
cylindrical portion
74, both central with the axis of the connector 70 as shown in Fig. 8. In
addition, an area 75
is provided in which to place an optical filter if desired for the particular
application of the
lamp. The point at which the transition is made from the conical portion to
the cylindrical
portion is the focus point of the light provided by reflector 40 through
window 17. The free
end of connector 15 is designed to receive a standard fiber optic coupling.
One advantage of
the present invention is that any type of coupling or adapter may be mated
with the lamp as it
is at ground potential.
The present invention also relates to improved methods of curing photocurable
resins and composites and whitening teeth using the arc lamp of the present
invention. For
curing applications, tungsten, halogen, and metal halide lamps are commonly
used because of
their relatively flat spectral distribution in the visible range. In addition,
it has been found
that visible light, particularly in the blue spectrum, is useful both for
curing and tooth
whitening applications. An optical filter is used to provide output light
primarily in the blue
range, i.e., approximately 470 nanometer wavelength.
In accordance with the present invention, improved methods of curing and tooth
whitening may be realized by using the arc lamp of the present invention
filled to 200 psig of
argon in these procedures. A short arc argon lamp filled to about 200 psig
exhibits a peak in
spectral output at about 470 nanometers. Thus, an argon arc lamp operating at
200 psig
provides for significantly improved efficiency in terms of delivering optical
energy in the blue
wavelength as compared with a xenon arc lamp. For example, with an input power
of 1500
watts, a minimum of 5 watts may be delivered from the lamp, through a light
guide to the
composite to be cured.
CA 02277088 1999-07-08
WO 98131043 PCT/US98/00167
14
The following conversion table shows the energy setting used with a lamp of
the present
invention as a function of the composite curing time recommended by the
manufacturer of the
composite, based on a conventional tungsten halogen curing light with an
output power of 500
mW/cm2 and a 0.950 cm~ probe (for a total output power of 475 mW). Also shown
in Table
1 are curing times for the system of the present invention, based on an
assumed power of S.0
watts at the distal end of a light guide, which is placed proximate the
composite to be cured.
It is likely that the actual power output is significantly higher, however, as
a fill of 200 psig
optimizes the output in the range of about 430-505 nanometers, so that the
curing times will
actually be even lower than those indicated.
Ta le 1
Joule Equivalents
for Manufacturer
Recommended
Curing Times
Recommended Joules for Composite CuringJoule Equivalent
Composite Curingconventional Time (for high (for high
Time (for curing pressure arc pressure arc
conventional light (based lamp) lamp)
curing light) on an
output power
of
475 mW)
10 seconds 4.75 0.3 seconds 1.5 Joules
seconds 9.50 0.6 seconds 3.0 Joules
seconds 14.25 0.9 seconds 4.5 Joules
20 40 seconds 19.0 1.2 seconds 6.0 Joules
50 seconds 23.75 1. S seconds 7.5 Joules
60 seconds 28.50 1.8 seconds 9.0 Joules
When the lamp of the present invention is used for both curing and whitening
25 applications, a filter may be used to reject undesirable wavelengths of
light and in a preferred
embodiment has the characteristics shown in Fig. 8, which illustrates the
percent transmission
as a function of wavelength. As indicated in this figure, the filter
substantially eliminates light
with a wavelength below about 430 nanometers and above about 505 nanometers
but transmits
light between these two wavelengths. As discussed above, reflector 40 may be
provided with
30 a dichroic filter to prevent infrared energy from being transmitted through
window 17. If a
reflector without a dichroic coating is used, a separate, dichroic filter may
be employed to
absorb and dissipate infrared energy.
CA 02277088 1999-07-08
WO 98/31043 PCT/US98/00167
As will be apparent to those of skill in the art, the actual curing time will
depend on the power levels of the optical energy delivered to the composite
(in the frequency
range passed by the filter), which in turn depend on the input power to the
arc lamp and the
fill pressure and specific gas or gases used.
5 The benefits of using a high powered light source in both curing and tooth
whitening applications -- in terms of both reducing the time required for the
procedures and
improving the results obtained -- are discussed in copending patent
application titled "Portable
High Power Arc Lamp System and Applications Therefor," filed December 24, 1996
by John
C. Cipolla, the disclosure of which is incorporated herein by reference. In
addition, the use
10 of the high pressure argon lamp of the present invention allows for
delivery of higher power
in desired frequency ranges and thus reduces the required power input.
In order to adapt the arc lamp of the present invention for use in curing and
tooth whitening applications, a light guide made from flexible material, such
as a bundle of
fiber optic cables housed inside a flexible sheath, may be attached to the
fiber optic connector
15 adapter 70. This permits the delivery of the output of the lamp to desired
tooth surfaces. In
a preferred embodiment, a more flexible, high power, solid state light guide
made from a
partially polymerized polymer is used, available from Translight of Pomfriet,
Connecticut.
Flexibility of the light guide is important to provide the user with
sufficient maneuverability of
the light guide. Therefore, several feet of light guide are required to
provide a sufficient
length for normal work conditions.
For tooth whitening applications, the lamp of the present invention may be
used
in conjunction with tooth bleaching compositions such as those containing
peroxide
compounds. Existing methods of tooth whitening use comparatively low powered
argon lasers
to activate the bleaching composition. Use of the present invention, which can
operate at
much greater power levels, will greatly reduce the time required for such
procedures and
improve the results because the faster the light energy is applied to, for
example, hydrogen
peroxide, the greater the amount of free oxygen radicals produced as opposed
to molecu'.ar
oxygen, which is far less effective in bleaching teeth.
The invention has been described in greatest detail with respect to the
particular
embodiments and exemplary applications described above. It is understood by
those of
ordinary skill in the art that changes may be made to the embodiments
described herein
CA 02277088 1999-07-08
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16
without departing from the broad inventive concepts thereof. The invention is
not limited by
this embodiment and examples, but is limited only by the scope of the appended
claims. For
example. the lamp of the present invention may be filled with any inert gas or
combination
thereof. The much higher pressure capacity of the lamp as compared with prior
art designs
allows for many more options than previously available with regard to the
ability to adjust the
gas fill to maximize output power in a particular frequency band. Moreover,
the higher power
outputs and superior heat dissipation capabilities of the lamp of the present
invention allow for
its use in every field in which low pressure, ceramic arc lamps, typically
filled with xenon
gas, are presently the lamp of choice, including infrared and visual
searchlights, fiber optic
illumination, spectroscopy, stadium lighting, stage and screen lighting,
automobile headlights,
surgical and other medical applications, and microscopy.
