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Patent 2000521 Summary

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(12) Patent Application: (11) CA 2000521
(54) English Title: HIGH EFFICACY ELECTRODELESS HIGH INTENSITY DISCHARGE LAMP EXHIBITING EASY STARTING
(54) French Title: LAMPE A DECHARGE A HAUTE INTENSITE, A GRAND RENDEMENT, SANS ELECTRODE, ET A DEMARRAGE FACILE
Status: Dead
Bibliographic Data
Abstracts

English Abstract


RD-18,813


HIGH EFFICACY ELECTRODELESS
HIGH INTENSITY DISCHARGE LAMP
EXHIBITING EASY STARTING
Abstract of the Disclosure
Improved ease of starting at room temperature while
maintaining high efficacy and good color rendition at white
color temperatures is achieved in an electrodeless metal
halide high intensity discharge lamp wherein a mercury-free
combination of arc tube fill materials may include sodium
iodide with or without cerium halide, and either krypton or
argon as a starting gas.


Claims

Note: Claims are shown in the official language in which they were submitted.


RD-18,813

The embodiments of the invention in which an exclu-
sive property or privilege is claimed are defined as follows:

1. A mercury-free electrodeless metal halide arc
lamp comprising:
a light transmissive arc tube for containing an
arc discharge;
a fill disposed in said arc tube to generate said
arc discharge, said fill including sodium iodide and a gas
selected from the group consisting of krypton and argon in a
sufficient quantity to limit the transport of thermal energy
from said arc discharge to the walls of said arc tube; and
excitation means for coupling radio-frequency
energy to said fill.

2. The lamp of claim 1 wherein the selected gas is
krypton in a quantity sufficient to provide a partial
pressure in the range of about 100-500 torr at room tempera-
ture.

3. The lamp of claim 1 wherein the selected gas is
argon in a quantity sufficient to provide a partial pressure
in the range of about 100-500 torr at room temperature.

4. The lamp of claim 1 wherein said fill further
comprises cerium halide, said halide being selected from the
group consisting of chlorides and iodides, said sodium
iodide and said cerium halide being present in weight
proportions to generate white color lamp emission.

5. The lamp of claim 4 wherein the weight proportion
of cerium halide is no greater than the weight proportion of
sodium iodide.

-14-


RD-18,813


6. The lamp of claim 4 wherein an amount of sodium
iodide is selected so that a reservoir of sodium iodide
condensate is present during lamp operation.

7. The lamp of claim 4 wherein an amount of cerium
halide is selected so that a reservoir of cerium halide
condensate is present during lamp operation.

8. The lamp of claim 4 wherein the selected amounts
of both sodium iodide and cerium halide provide a reservoir
of mixed condensates during lamp operation.

9. The lamp of claim 4 wherein the selected gas is
Krypton in a quantity sufficient to provide a partial
pressure in the range of about 100-500 torr at room tempera-
ture.

10. The lamp of claim 4 wherein the selected gas is
argon in a quantity sufficient to provide a partial pressure
in the range of about 100-500 torr at room temperature.

11. The lamp of claim 9 wherein the selected cerium
halide is cerium iodide.

12. The lamp of claim 9 wherein the selected cerium
halide is cerium chloride.

13. The lamp of claim 10 wherein the selected cerium
halide is cerium chloride.

14. The lamp of claim 10 wherein the selected cerium
halide is cerium chloride.

-15-

RD-18,813


15. A mercury-free electrodeless metal halide arc lamp
comprising:
a light transmissive arc tube for containing an
arc discharge, said arc tube being cylindrically-shaped with
the height of said arc tube being less than its outside
diameter;
a light transmissive outer envelope disposed
around said arc tube and defining a space therebetween;
a fill disposed in said arc tube to generate said
arc discharge, said fill including sodium iodide and cerium
halide, said halide being selected from the group consisting
of chlorides and iodides, said sodium iodide and cerium
halide being present in weight proportions to generate white
color lamp emission;
said fill further including a gas selected from
the group consisting of krypton and argon in a sufficient
quantity to provide a partial pressure in the range of about
100-500 torr at room temperature; and
excitation means for coupling radio-frequency
energy to said fill.

16. The lamp of claim 15 wherein the space between the
light transmissive outer envelope and said arc tube is
evacuated.

17. The lamp of claim 15 wherein the space between the
light transmissive outer envelope and said arc tube is
occupied with thermal energy barrier means.
18. The invention as defined in any of the preceding claims
including any further features of novelty disclosed.

-16-



Description

Note: Descriptions are shown in the official language in which they were submitted.


RD-18,813

2~ C~

HIGH EFFICACY ELECTROD~LESS
HIGH INTENSITY DISCHARGE LAMP
EXHIBITING EASY STARTING

Related Patent AppLications

In Dakin and Johnson United States Patent No.
i9SU~' , and assigned to the
assignee of the present invention, an electrode type lamp
utilizing sodium iodide and xenon buffer gas as the arc tube
~ fill material is disclosed. In that application it is
recognized that xenon buffer gas exerts a favorable influ-
ence on the sodium D-line spectrum and also prevents the
tie-up of halide which occurs in prior art lamps when a
mercury buffer gas is employed.
In Dakin, Anderson and Battacharya United States Patent
Number 4,783,615 which issued November 8,198~ and also
assigned to the present assignee, an electrodeless type
sodium iodide arc lamp is disclosed wherein the arc tube
lS fill comprises sodium iodide, mercury iodide, and xenon in a
sufficient quantity to limit chemical transport of energy
from the plasma discharge to the walls of said arc tube. In --
the arc tube fill, the mercury iodide is present in a
guantity less than the quantity of sodium iodide but suffi-
cient to provide an amount of free iodine near the arc tube
walls when the lamp is operating. The sodium iodide in the
arc tube fill can also be present in sufficient quantity to
provide a reservoir of condensate during lamp operation.
In Johnson, Dakin and Anderson Canadian application
Serial No. 578,095 filed September 22, 1988, and assigned to
the present assignee, an electrodeless type high intensity
discharge lamp is disclosed wherein a mercury-free arc tube
fill comprises sodium halide, cerium halide in weight
proportion no greater than the weight proportion of sodium

--1--




- '~

"

RD-18,813
Z~, C~S,.z~.~

halide in the fill, and a reservoir of these fill materials
in the arc tube to compensate for any loss of the individual
constituents during lamp operation. High pressure xenon
buffer gas is present in sufficient guantity to limit the
transport of thermal energy by conduction from the arc
discharge to the walls of the arc tube, as well as to
function as a starting gas.
Since the present invention represents still further
improvements in the electrodeless form of the aforementioned
high intensity discharge metal halide lamp and employs some
of the same arc tube materials, all three of the aforemen-
tioned co-pending patent applications are specifically
incorporated herein by reference.

Bac~ground of the Invention
This invention relates generally to high intensity
discharge lamps wherein the arc discharge is generated by a
plasma in a solenoidal electric field and more particularly
to use of a new buffer gas employed in the arc tube fill in
combination with sodium iodide or the combination of sodium
iodide and cerium halide to improve starting performance
without adversely affecting lamp efficacy or color rendi-
tion. Lamp efficiency or "efficacy", as used in the present
application, means luminous efficacy as measured in conven-
tional terms of lumens per watt. As to color rendition,
general purpose illumination requires that objects illumi-
nated by a particular light source display much the same
color as when illuminated by natural sunlight. Such
requirement is measured by known standards such as the
C.I.E. color rendering index values (CRI), and CRI values of
50 or greater are deemed essential for commercial accepta-
bility of lamps in most general lighting applications. A
still further requirement for commercially acceptable

RD-18,813
2il~ '(iS.~

general purpose illumination is the white color temperature
provided wit~ such lamp, which is fixed at about 3000K for
the warm white lamp, about 3500K for the standard white
lamp and about 4200K for the cool white lamp, as measured
by the C.I.E. chromaticity x and y values.
The lamps described in the present invention are part
of the class referred to as high intensity discharge lamps
(HID) becauce in their basic operation a medium to high
pressure gas is caused to emit visible wavelength radiation
upon excitation typically caused by passage of current
through an ionizable gas such as sodium vapor or mixed
sodium vapor and cerium vapor. The original class of such
HID lamps was that in which the discharge current was caused
to flow between a pair of electrodes. Since the electrode
members in such electroded HID lamps were prone to vigorous
attack by the arc tube fill materials, causing early lamp
failure, the more recently developed solenoidal electric
field lamps of this type have been proposed to broaden the
choice of arc tube materials through elimination of the
electrode component. Such more recently developed solenoi-
dal electric field lamps are described in J.M. Anderson U.S.
Patent Nos. 4,017,764 and 4,180,763, and Chalek and Johnson
U.S. Patent No. 4,591,7S9, all assigned to the assignee of
the present invention, and generate a plasma arc in the arc
tube comoonent during lamp operation, all in a previously
known manner.
Conventional electrodeless HID lamps suffer from the
disadvantage that they are difficult to start. This is
because the xenon buffer gas also functions as the starting
gas. ~owever, xenon is difficult to start, especially when
used at a high pressure, such as 200 torr, as compared with
the more conventional starting gas pressures of 30 torr or
less. The difficulty of starting high-pressure xenon,

RD-18,8i3
2i J / ~ S.~,

combined with the low solenoidal electric field available
from the lamp induction coil, has heretofore made room
temperature HID lamp starting impossible.
One method that has been used for starting HID lamps
involves immersing the arc tube in liquid nitrogen so as to
condense most of the xenon. Thereafter, the induction coil
current is increased, and the lamp usually starts at a
current of 18 amps or less. If necessary, a spark coil is
used to apply high-voltage pulses to help start the dis-
charge. Once the lamp is started, heat from the dischargeevaporates the condensed xenon and normal xenon pressure is
reached.
~ he liquid nitrogen method is effective because there
is an optimum xenon pressure for starting the discharge.
While this optimum pressure is not known with great preci-
sion for the above stated starting conditions, it is never-
theless well below 200 torr and above the saturation vapor
pressure of xenon (2.5 millitorr) at the temperature of
liquid nitrogen (77K). Since the liquid nitrogen starting
method is clearly not practical for commercial lamps, it is
desirable to employ a more practical starting method for
room-temperature operated HID lamps.

Obiects of the Invention
One object of the invention is to buffer chemical
transport of energy from the plasma arc to the arc tube
walls in an electrodeless sodium iodide or sodium
iodide/cerium halide arc discharge lamp with krypton starting
gas.
Another object of the invention.is to buffer chemical
transport of energy from the plasma arc to the arc tube
walls in an electrodeless sodium iodide or sodium


-4-
.

~ RD-18,813
(r~

iodide/cerium halide arc discharge lamp with argon starting
gas.
Another object of the invention is to improve the ease
of starting an electrodeless arc discharge lamp while
maintaining high efficacy and good color rendition.
Still another object of the invention is to optimize
the starting and operating performance of an electrodeless
sodium iodide or sodium iodide/cerium halide arc lamp at
room temperature.

Summar~ of the Invention
In accordance with the invention, a particular combina-
tion of fill materials in the arc tube of an electrodeless
metal halide arc lamp is used to provide white color lamp
emission at improved efficacy and color rendition, accompa-
nied by reliable starting in a room temperature ambient.More particularly, this improved lamp features a light
transmissive arc tube containing a mercury-free fill com-
prising sodium iodide or a mixture of sodium iodide and
cerium halide, along with either krypton gas or argon gas in
the proper weight proportion to generate white color lamp
emission at an efficacy of 200 lumens per watt (LPW) or
greater and accompanied by color rendering indices (CRI) of
at least 50. The white color temperature for the improved
lamps extends from about 3000K up to about 5000R so that
such lamps are suitable for general illumination purposes.
Useful cerium halides in the sodium iodide/cerium halide
mixture employed as the lamp fill can be selected from the
group consisting of chlorides and iodides, including mix-
tures thereof such as cerium chloride (CeC13) and cerium
iodide (CeI3). The weight proportion of cerium halide is
maintained no greater than the weight proportion of sodium
iodide in the fill in order to provide the aforementioned




.

.

RD-18,813
2ii~

characteristics, with a reservoir of these fill materials in
the arc tube be ng desirable to compensate for any loss of
the individual constituents during lamp operation. With
respect to the relative weight proportions of the aforemen-
tioned sodium iodide and cerium halide mixture, it has beenfound that too much sodium iodide lowers CRI values whereas
too much cerium halide iowers lamp efficacy. The composite
white color lamp emission provided with the aforementioned
mixture of fill materials results mainly from otherwise
conventional high pressure sodium discharge emission to
which has been added visible radiation provided by cerium
halide which extends in ~ continuous manner over the 400-700
nanometer visible wavelength region.
The improvement in starting is attributable to main-
taining controlled proportions of krypton gas or argon gas
in the lamp fill. Specifically, the replacement of xenon
with krypton or argon at high pressures allows the krypton
or argon to serve as a barrier or buffer against undesirable
transport of thermal energy from the arc discharge to the
arc tube walls so as to preserve the efficacious radiation
output and other benefits attainable when utilizing xenon as
both a buffer gas and a starting gas, while at the same time
rendering room temperature starting of the lamp easier and
more reliable.
The amount of krypton or argon employed in the present
arc tube fill to achieve the above noted lamp starting
performance gains must be sufficient to provide a partial
pressure in the range of about 100-500 torr at room tempera-
ture.
A preferred lamp structural configuration utilizing the
above disclosed arc tube materials to optimize lamp starting
performance features a cylindrically-shaped arc tube of a
height less than its outside diameter, a light transmissive




:
-
.

-

RD-18,813

Z~J~

outer envelope disposed around the arc tube and defining a
space therebetween, and excitation means for coupling
radio-frequency energy to the arc tube fill. The arc tube
is preferably formed of a high temperature glass, such as
fused quartz, or an optically transparent ceramic, such as
polycrystalline alumina. A plasma arc is generated inside
the filled arc tube during lamp operation by excitation from
a solenoidal electric field associated with the lamp, all in
known manner. The excitation is created by a magnetic
- 10 field, changing with time, to establish within the tube an
electric field which closes completely upon itself, resulting
in the light-producing high intensity discharge. The
excitation source in the preferred lamp design comprises an
induction coil disposed around the outside of the outer lamp
envelope and connected to a power supply through an imped-
ance matching network. The spacing between the arc tube and
outer envelope in the preferred lamp device can be occupied
by thermal energy barrier means, such as metal baffles or
quartz wool, or even a vacuum. Such thermal barrier means
desirably reduces heat loss from the lamp.

Brief Description of the Drawinqs
The novel features of the invention are set forth with
particularity in the appended claims. The invention itself,
however, as to organization and method of operation, together
with further objects and advantages thereof, may best be
understood by reference to the following description taken
in conjunction with the accompanying drawings in which:
Figure 1 is a cross-sectional side view depicting an
electrodeless lamp configuration of the present invention
together with apparatus for exciting the lamp fill; and




:

RD-18,813
Zl~ 5~'!1.

Figure 2 is a graphical depiction of the approximate
discharge current-voltage characteristic for xenon at
200 torr.

Detailed Descri~tion of the Preferred Embodiment
Figure 1 depicts an electrodeless arc discharge lamp
which includes an arc tube 10 for containing a fill 11. Arc
tube 10 comprises a light-transmissive material, such as
fused quartz or a refractory ceramic material such as
sintered polycrystalline alumina. An optimum shape for arc
tube 10, as depicted, is a flattened spherical shape or a
short cylindrical (e.g. hockey puck or pillbox) shape with
rounded edges. The diameter of arc tube 10 is greater than
its height dimension. A light-transmissive outer enve-
lope 12, which may be comprised of quartz or a refractory
ceramic, is disposed around arc tube 10. Convective cooling
of arc tube 10 is limited by outer envelope 12. A blanket
of quartz wool 15 may also be provided between arc tube 10
and outer envelope 12 at the bottom and sides of the arc
tube to further limit cooling. Quartz wool 15 is comprised
of thin fibers of quartz which are nearly transparent to
visible light but which diffusely reflect infrared radia-
tion.
A primary coil 13 and a radio-frequency (RF) power
supply 14 are employed to excite a plasma arc discharge in
fill 11. As previously indicated, this configuration
including primary 13 and RF power supply 14 is commonly
referred to as a high intensity discharge solenoidal elec-
tric field (HID-SEF) lamp. The SEF configuration is essen-
tially a transformer which couples radio-frequency energy to
a plasma, the plasma acting as a single-turn secondary for
the transformer. An alternating magnetic field which
results from the RF current in primary coil 13 creates an

RD-18,813
2~ 5~.

electric field in arc tube 10 which closes upon itself
completely. Current flows as a result of the electric field
and an arc discharge results in arc tube 10. Since
a more detailed description for such HID-SEF lamp
structures is found in previously cited United States
Patent No. 4,017,764 and in United States Patent
Number 4,180,763. An exemplary frequency of
operation for RF power supply 14 is 13.56 megahertz.
Typical power input to the lamp can be in the range of
100-2000 watts.
The problem of starting an electrodeless HID lamp
employing xenon as a starting gas is illustrated by the
curve shown in Figure 2. As the initial discharge current
increases from zero, much higher electric fields have to be
applied to the discharge than during steady state operation,
where sodium iodide or sodium iodide/cerium iodide elec-
trodeless lamps operate at discharge levels of approximately
lO amps and 10 volts per centimeter. After the discharge
current has increased above approximately 1 milliamp, the
electric field necessary to sustain the arc discharge
decreases to a value well below that needed to initiate the
discharge. While the discharge characteristic for xenon at
200 torr is not known accurately, tests have shown that the
electric field required for starting is higher than what can
be obtained from an electromagnetic induction coil of
reasonable size and power loading. For example, using an
arc tube such as shown in Figure 1 with a 20 millimeter
outside diameter and 17 millimeter outer height, an induc-
tion coil made from 1j8" diameter copper tubing with seven
turns, a central opening of 26 millimeters in diameter and
an impedance of 145 ohms at 13.56 MHz can produce a solenoi-
dal electric field in the discharge region of approximately
20 volts per centimeter at the maximum safe coil current of



.. -- - ~ :

RD-18,813

21~ 5~1 -

18 amps. This field is too low to start the electrodeless
lamp with a xenon buffer gas in the fill.
The following examples are provided to demonstrate
other, successfully tested arc tube Eills for the present
metal halide arc lamp. In all five examples, the arc tube
had a rounded cylindrical shape, with a 20 millimeter
outside diameter and 17 millimeter outer height.

EXAMPLE I
An arc tube was filled with 4.0 milligrams NaI, 2.0
milligrams CeI3, and approximately 250 torr partial pressure
of krypton gas at room temperature. The lamp started at
room temperature and operated at approximately 218 watts
input power to produce 207 LPW and a 52 CRI value.

EXAMPLE I I
An arc tube was filled with approximately 3.8 milli-
grams NaI, 2.0 milligrams CeI3, and 250 torr partial pres-
sure of krypton gas at room temperature. The lamp started
at room temperature and operated at approximately 243 watts
input power to provide 198 LPW efficacy and a 54 CRI value.

For purposes of comparing normal operation of the lamps
having a krypton starting gas, the following three examples
were performed using xenon as the starting gas.

EXAMPLE I I I
In this example, the arc tube fill consisted of approx-
imately 6.3 milligrams NaI and 2.8 milligrams CeI3 along
with xenon gas at a partial pressure of approximately
250 torr at room temperature. When supplied with 244 watts
input power, the lamp exhibited 202 LPW and a 50 CRI value.


--10--




,

RD-18,813
Zq~

EXAMPLE IV
An arc tube was filled with 6.5 milligrams NaI, 3.1
milligrams CeCl3, and 500 torr partial pressure of xenon at
room temperature. At 260 watts input power the lamp pro-
5 duced 205 LPW and a 51 CRI value.

EXAMPLE V
An arc tube was filled with approximately 6.0 milli-
grams NaI, 2.3 milligrams CeC13, and 500 torr partial
pressure of xenon at room temperature. When operated at 265
10 watts input power, the lamp produced 203 LPW at a 54 C~I
value.

As to ease of starting, three lamp fills were tested in
an arc tube comprised of a rounded cylinder of fused quartz
having an outside diameter of 20 millimeters and an outside
15 height of 17 millimeters. The lamp fills all contained
6 milligrams NaI, 3 milligrams CeI3 and a starting gas of
either xenon or krypton.
Five turns of copper bar (2.5 x 3.8 millimeters) were
wound to form a solenoid of 20 millimeters bore to fit the
20 arc tubes fairly tightly. A spark coil was used to provide
the initial ionization. Current in the induction coil was
gradually raised while ~bserving the arc tube. The current
levels were recorded at which a sustained glow discharge and
the full high-current SEF mode appeared. The results for
25 three lamps are as follows:

RD-18,813
2~Jt,J~!;s~



Coi1 CurrentCoil Current
for for
Inert Gas Sustained SEF
Lam~ No. Gas PressureGlow Mode Mode
5 W-73 xenon 250 torr28 amps 28 amps
W-72 xenon 500 torr35 amps 35 amps
W-75 krypton 500 torr 28 amps 29 amps

Thus it is evident that for the two xenon-containing lamps,
starting was easier at 250 torr than at 500 torr; however,
the higher pressure (500 torr) krypton-containing lamp was
easier to start than the 500 torr xenon-containing lamp,
reducing the current level required in the induction coil
for lamp starting from 35 amps to 29 amps.
Finally, an electrodeless lamp of rounded cylindrical
shape and comprised of fused quartz having an outside
diameter of 20 millimeters and an outside height of 17
millimeters was filled with 6 milligrams NaI, 3 milligrams
CeI3 and argon starting gas at 250 torr partial pressure.
Although this lamp started even easier than comparable
krypton-containing lamps, its efficacy was approximately 10%
lower than that of similar krypton-containing or xenon-
containing lamps. Hence argon can be employed to provide
easier starting than krypton, but wit~ a reduction in
efficacy as a trade-off.
Thus HID lamps of the new type herein described can be
started into the full SEF mode without use of liquid nitro-
gen or of internal starting probes, and without adverse
effect on lamp operation, at coil currents significantly
below those required for starting HID lamps employing xenon
as a buffer gas (and also a starting gas).


-12-

RD-18,813
2~ 5~ :

The HID-SEF lamps of the present invention thus exhibit-
optimum performance when containing the combination of arc
tube fill materials including sodium iodide, with or with-
out, cerium halide, and with either krypton or argon starting
gas. As has been shown, efficacy of over 200 LPW is obtained,
accompanied by CRI values of 50 or greater.
The foregoing describes a broadly useful, improved HID
electrodeless lamp exhibiting superior starting performance
without adverse effect on normal operation. The invention
~ 10 is relevant to fills including sodium iodide, or a mixture
of sodium iodide and cerium halide, as a starting gas.
While only certain preferred features of the invention
have been illustrated and described herein, many modifica-
tions and changes will occur to those skilled in the art.
It is, therefore, to be understood that the appended claims
are intended to cover all such modifications and changes as
fall within the true spirit of the invention.




.. . . . _ _

.
.

Representative Drawing
A single figure which represents the drawing illustrating the invention.
Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date Unavailable
(22) Filed 1989-10-12
(41) Open to Public Inspection 1991-04-12
Examination Requested 1994-02-09
Dead Application 1996-04-14

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Application Fee $0.00 1989-10-12
Registration of a document - section 124 $0.00 1990-04-12
Maintenance Fee - Application - New Act 2 1991-10-14 $100.00 1991-09-19
Maintenance Fee - Application - New Act 3 1992-10-12 $100.00 1992-09-03
Maintenance Fee - Application - New Act 4 1993-10-12 $100.00 1993-09-16
Maintenance Fee - Application - New Act 5 1994-10-12 $150.00 1994-09-15
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
GENERAL ELECTRIC COMPANY
Past Owners on Record
WITTING, HARALD LUDWIG
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Drawings 1991-04-12 1 23
Claims 1991-04-12 3 95
Abstract 1991-04-12 1 15
Cover Page 1991-04-12 1 15
Representative Drawing 1999-07-16 1 12
Description 1991-04-12 13 499
Fees 1991-09-19 2 70
Fees 1994-09-15 1 51
Fees 1992-09-03 1 38
Fees 1993-09-16 1 39