U.S. patent number 3,898,504 [Application Number 05/416,015] was granted by the patent office on 1975-08-05 for high pressure metal vapor discharge lamp.
This patent grant is currently assigned to Matsushita Electronics Corporation. Invention is credited to Hidezoh Akutsu, Shoichi Baba, Takio Okamoto, Yoshiaki Watarai, Haruo Yamazaki.
United States Patent |
3,898,504 |
Akutsu , et al. |
August 5, 1975 |
High pressure metal vapor discharge lamp
Abstract
An electric discharge lamp having an excellent color rendition
with a color acceptability higher than 1.0, a relatively high
luminous efficacy and a good life performance, is provided, in a
high pressure metal vapor lamp using a polycrystalline alumina
ceramic tubing as the arc tube envelope within which sodium as a
metal for producing radiant emission, mercury or cadmium as a
buffer gas and xenon as a starting inert gas are contained, by
controlling such quantities which are variable in the design of the
high pressure metal vapor discharge lamp as the lamp wattage W in
watts, an increased internal diameter of the arc tube envelope of
the lamp d in millimeters, the interelectrode gap length L in
millimeters and a lowered average potential gradient of the arc
tube E in volts per centimeter in such a manner that they may
satisfy the relations: 25 .gtoreq.e .gtoreq.37.7 - 2.05d (but, d
>9) And ##EQU1##
Inventors: |
Akutsu; Hidezoh (Ashiya,
JA), Yamazaki; Haruo (Shiga-ken, JA),
Okamoto; Takio (Kusatsu, JA), Watarai; Yoshiaki
(Takatsuki, JA), Baba; Shoichi (Takatsuki,
JA) |
Assignee: |
Matsushita Electronics
Corporation (Osaka, JA)
|
Family
ID: |
27311568 |
Appl.
No.: |
05/416,015 |
Filed: |
November 15, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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204866 |
Dec 6, 1971 |
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Foreign Application Priority Data
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Dec 9, 1970 [JA] |
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45-109842 |
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Current U.S.
Class: |
313/620;
313/639 |
Current CPC
Class: |
H01J
61/30 (20130101); H01J 61/22 (20130101); H01J
61/825 (20130101) |
Current International
Class: |
H01J
61/30 (20060101); H01J 61/00 (20060101); H01J
61/22 (20060101); H01J 61/82 (20060101); H01J
61/12 (20060101); H01j 061/30 (); H01j
061/18 () |
Field of
Search: |
;313/183,184,214,220,221,225,229 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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485,274 |
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May 1938 |
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GB |
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106,842 |
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Mar 1939 |
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AU |
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Primary Examiner: Lawrence; James W.
Assistant Examiner: LaRoche; E. R.
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation-in-part application of the U.S. Ser. No.
204,866 filed Dec. 6, 1971 and now abandoned.
Claims
We claim:
1. A high pressure sodium vapor discharge lamp comprising a tube
envelope containing therein sodium, inert starting gas, buffer gas
comprising at least one of mercury and cadmium and discharge
electrodes sealed in said envelope, said lamp satisfying the
following relation between the tube diameter d in millimeters and
an average potential gradient E in volts per centimeter
E.gtoreq.37.7 - 2.05d,
wherein E.ltoreq.25 and d>9.
2. A high pressure metal vapor discharge lamp using a translucent
polycrystalline alumina ceramic tubing as the lamp envelope within
which are contained sodium as metal for producing radiant emission,
at least one of mercury and cadmium as a source of buffer gas,
xenon as an inert starting gas and discharge electrodes sealed in
said envelope, wherein the operating voltage E of the lamp is lower
than such a critical value V.sub.LO in volts of the lamp voltage
that an economical ballast can be designed, and the lamp wattage W
in watts, the lamp diameter d in millimeters and the interelectrode
gap length L in millimeters simultaneously satisfy the following
conditions: ##EQU10## wherein E.ltoreq.25 and d>9, ##EQU11##
3. A high pressure metal vapor discharge lamp as claimed in claim
2, wherein said critical value V.sub.LO is 130 volts.
4. A high pressure metal vapor discharge lamp as claimed in claim
3, wherein said critical value V.sub.LO is 0.6 Vs, where Vs is a
voltage value in volts of the power supply line.
5. A high pressure metal vapor discharge lamp as claimed in claim
3, wherein said critical value V.sub.LO is 140 volts.
6. A high pressure metal vapor discharge lamp using a
polycrystalline alumina ceramic tubing as the arc tube envelop
within which are contained sodium metal for producing radiant
emission, a buffer gas comprising at least one of mercury and
cadmium, inert starting gas and discharge electrodes sealed in said
envelope, wherein the lamp wattage W in watts, the lamp diameter d
in millimeters, the interelectrode gap length L in millimeters and
the average potential gradient E in volts per centimeter
simultaneously satisfy the following conditions:
E.gtoreq. 37.7 - 2.05d,
wherein E.ltoreq.25 and d>9, ##EQU12## whereby an excellent
color rendition with a color acceptability higher than 1.0 is
obtained with discharge of said lamp.
7. A high pressure metal vapor discharge lamp as claimed in claim
6, wherein said buffer gas consists essentially of cadmium.
8. A high pressure metal vapor discharge lamp as claimed in claim
6, wherein said buffer gas consists essentially of mercury.
9. A discharge lamp as claimed in claim 1, wherein the diameter d
is given in a range 9.ltoreq.d.ltoreq.13.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a high pressure metal
vapor discharge lamp using a polycrystalline alumina ceramic tube
which is translucent and within which metal for producing radiant
emission, buffer gas and inert starting gas are placed, and more
particularly to the structure of such a lamp with which the vapor
of the metal in the lamp can be maintained at a high pressure.
2. Description of the Prior Art
Since the polycrystalline alumina ceramic used for the arc tube
envelope can withstand the attack of metal vapor at high
temperatures and high pressures, as is disclosed for example in the
U.S. Pat. No. 3,248,590, a high pressure metal vapor lamp discharge
with a polycrystalline alumina ceramic envelope has been widely
used in the practical field.
One typical example of such high pressure metal vapor discharge
lamps is a high pressure sodium lamp which utilizes sodium as a
metal for producing radiant emission. The high pressure sodium lamp
produces yellowish-white radiant emission consisting of a
continuous spectrum covering the whole visible region, while the
conventional sodium lamp of low pressure type radiates mainly a
yellow light corresponding to the sodium D lines. Therefore, from
the standpoint of color rendition, the former may excel the latter
but may still be surpassed by the conventional fluorescent lamp or
the metal halide lamps.
The spectral distributions of radiant emission from a sodium vapor
discharge lamp tend to broaden gradually over the entire visible
region with rising sodium vapor pressure, so that the color
rendition is also improved. A conventional high pressure sodium
lamp operated at sodium vapor pressure of 100 to 200 Torr has a
color temperature of about 2,100.degree.K and a general color
rendering index of about 30. Furthermore, a sodium vapor discharge
lamp which is operated at a higher power input and sodium vapor
pressure of higher than 300 Torr, will achieve color temperatures
of 2,300.degree. to 3,500.degree.K and general color rendering
indices of about 70 to 90. Moreover, it is also observed that the
color acceptability of the discharge lamp with higher sodium vapor
pressure is over 1.0. However, the increase in sodium vapor
pressure might accelerate the reaction between sodium and the
alumina envelope, which results in a bad life performance of the
lamp. Moreover, the lamp voltage must be increased, so that an
uneconomical ballast of a large size and with a very high open
voltage is needed for operating the lamp. Thus, such a sodium vapor
discharge lamp will be essentially disadvantageous from the life
performance and the economic point of view, as compared with a
conventional high pressure sodium lamp.
SUMMARY OF THE INVENTION
One object of the present invention is to propose a high pressure
metal vapor discharge lamp capable of providing a good color
rendition and a relatively high luminous efficacy, while holding a
good life performance.
Another object of the invention is to provide a specific arc tube
structure of the lamp having an increased lamp diameter, with which
a good color rendition can be realized even by such a low lamp
voltage that the lamp can be operated on an economical ballast.
For further objects and features and for a better understanding of
the invention, attention is now directed to the following
description of a preferred embodiment taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial sectional view of a metal vapor discharge lamp
illustrating an exemplary lamp structure embodying the
invention.
FIG. 2 is a graph illustrating the characteristic of the lamp in
accordance with the invention in which the curve represents a
function connecting the average potential gradient in the lamp
envelope and the internal diameter of the arc tube.
FIG. 3 illustrates graphically the relation between internal
diameter of the arc tube and luminous efficacy.
FIG. 4 illustrates graphically the relation between lamp per unit
length of the interelectrode gap length and luminous efficacy of a
metal vapor lamp discharge embodying the invention.
FIG. 5 illustrates graphically the relation between internal
diameter of the arc tube and lamp wattage per unit length of the
interelectrode gap length of a metal vapor discharge lamp embodying
the invention.
FIG. 6 illustrates graphically a comparison between the lamp
voltage characteristics through the performances of the discharge
lamps according to the invention and the prior art.
We, the inventors have performed a series of tests with discharge
lamps using sodium as a light producing medium, that is, a high
pressure sodium lamp, in which various lamp characteristics are
investigated by varying the diameter and length of the arc tube
envelope but with the quantities of sodium, mercury and inert gas
in the arc tube being constant. As a result there have been
revealed general tendencies as described in the following.
1. For a constant color temperature, luminous efficacy increases
with decreasing lamp diameter, while luminous efficacy also
increases with increasing lamp wattage per unit length of the arc
tube.
2. Lamp wattage per unit length in excess of a certain limiting
level adversely affects the life of lamp. Namely, the lamp voltage
rises and the luminous flux shows a relatively large decrement
during life, and in some extreme cases there is caused blackening
of the arc tube envelope and a shift in the color of emitted light
due to loss of sodium in the arc tube envelope.
3. For a constant color temperature, the average potential gradient
of the arc of the lamp, which represents indirectly the vapor
pressure in the arc tube, decreases with increasing lamp diameter.
It is asserted from the inventors' experiments that the average
potential gradient of arc must not be made higher than about 25
V/cm in order to obtain a good performance. This is, for the first
time, made possible by using a lamp tube of a diameter larger than
that of the usual high pressure sodium vapor lamps.
Considering the results obtained through the repeated experiments,
the inventors have reached the conclusion that if the relation of
the lamp wattage to the interelectrode gap length of the arc tube
and the lamp diameter is appropriately controlled a preferred lamp
structure can be obtained which is well balanced from the
standpoint of the above mentioned tendencies. Namely, selecting the
values for the average potential gradient E (Volts/cm), the
interelectrode gap length of the arc tube L (mm), the internal
diameter of the arc tube envelope d (mm) and the lamp wattage W
(watt) such that
25.gtoreq. E.gtoreq. 37.7 - 2.05d (but, d>9) (I), ##EQU2## one
can attain the object of the present invention.
Reference should now be made to FIG. 1 which shows the structure of
an arc tube of the lamp embodying the invention. In the figure,
into the ends of a polycrystalline alumina ceramic tube 1 serving
as an arc tube envelope are inserted ceramic end caps 2 for
hermetic sealing, and niobium tubes 3, used as electrode
lead-in-wires, pass through central perforations of the caps 2 at
the ends of the lamp, and discharging electrodes 4 are soldered to
the inner ends of the niobium tubes 3.
The inventors have made measurements of various lamp
characteristics, assuming several combinations of the values for
the internal diameter d of the arc tube, the interelectrode gap
length of the arc tube L, and the quantities of sodium, and mercury
or cadmium as buffer gas, taken from the following table. In all
these cases Xenon is contained in the lamp to serve as an inert
starting gas.
______________________________________ d (mm) 6.3, 7.0, 7.6, 9.7,
11.5, 13.5 L (mm) 40, 60, 82, quantity of sodium (mg) 15, quantity
of mercury (mg) 3, 7.5, 30, 40, 50, 60, quantity of cadmium (mg)
10, 20, 30, 40, 60, 80, ______________________________________
FIGS. 2 to 5 illustrate in graphical fashion the various lamp
characteristics for lamps constructed for trial measurements on the
basis of the possible combinations as mentioned above. The thorough
and synthetic consideration of these characteristics will lead to
the following results.
A. The average potential gradient E of the arc of the lamp, that
is, the lamp voltage divided by the interelectrode gap length,
decreases with increasing arc tube diameter d if the color
acceptability is kept at the same level. In order to obtain a color
acceptability of higher than 1.0, the relation between the average
potential gradient E and arc tube lamp diameter d must be such that
E.gtoreq. 37.7 - 20.5d, as apparent from FIG. 2.
FIG. 2 means that the lamp with the larger internal diameter of the
arc tube can provide a good color rendition by a lower lamp
voltage, that is, a lower sodium vapor pressure in the arc tube.
Increasing the internal tube diameter, on the other hand, makes it
possible to reduce the reignition voltage of the lamp and therefore
the open voltage of the ballast with which the lamp is operated.
Consequently, by utilizing an arc tube envelope with a large
internal diameter, the life performance of the lamp might be
improved and moreover the lamp can be operated on an economical
ballast (of lower power loss, lighter weight and lower cost) as
compared to conventional high pressure discharge lamps.
On the other hand, it is asserted from the inventors' experiments
that the average potential gradient of the arc must not be made
higher than about 25 V/cm in order to obtain a good performance
characteristic in co-operation with such an economical ballast.
Further it is asserted that the use of the lamp of a diameter not
smaller than 9 mm is indispensable when consideration is made to
the possible variations between the lamp electrodes or in the lamp
characteristics through its performance. It is noted that the
conventional high pressure sodium lamps have a diameter ranging
from 6 to 8 mm. Therefore the lamp intended by the invention is,
for the first time, achieved by using a lamp tube having a diameter
exceeding the range. Accordingly, the average potential gradient E
is given as 25.gtoreq. E.gtoreq. 37.7 - 2.05d (but, d>9). This
relation is given by the preceding condition (I).
The inventors' experiments, with respect to the range of the
diameter d, have resulted in a comparative graph as indicated in
FIG. 6. The characteristic curve A (thick line) of FIG. 6 shows a
performance of a first group of test lamp tubes which has a 9 mm
lamp diameter and 65 mm interelectrode gap. The characteristics
curve B (dotted line) of FIG. 6 shows a performance of a second
group of test lamp tubes which has a 9.5 mm lamp diameter and 60 mm
interelectrode gap. Both lamp tubes were fabricated as a trial by
the inventors and have an equal lamp wattage, i.e. 400 watts.
As clear from the comparative graph, the lamp voltage along the
characteristic curve A quickly increases after the 3,000 burning
hours. This quick increase of the lamp voltage also brought about a
considerable reduction in the light emission of the lamp. Thus it
was concluded that the design of the lamp tube having the
characteristic A could not be practically employed. In contrast the
curve B shows the lamp voltage which almost uniformly increases
along an easy slope. This increase of the lamp voltage brought
about little reduction in the light emission of the second test
tube. About 85 percent of lumen-maintenance of this tube was
confirmed after 6,000 burning hours. Thus it is concluded that the
design of d = 9.5 mm ensures the desirable lamps for practical use
having a service life of 6,000 hours. In order to obtain the
measurements of the graph of FIG. 6, as mentioned above, the two
groups of several sample lamps were respectively prepared for the
case where d is equal to 9.0 mm and l equal to 65 mm and for the
case where d is equal to 9.5 mm and l equal to 60 mm. Each
point-mark on the curves A and B represents the arithmetic mean
value of the lamp voltages which were measured on the respective
group of sample lamps at the corresponding time of burning hour.
The vertical line indicated through each point-mark represents a
range of distribution of the lamp voltages of the respective group
measured at the corresponding time of burning hour. The upper and
lower ends of each vertical line represent the upper and lower
limits of the lamp voltages measured.
For better understanding brief explanation of the term "color
acceptability" used herein should now be made. The chromaticness of
rendered colors of 8 CIE test samples by the test lamp according to
the invention, are connected with one another by line segments to
form an octagon, on the chromaticness (U*, V*) plane, the area of
which is represented by St. In like manner, another similar octagon
whose area is given by Sr, is formed by the reference illuminant of
the same color temperature to that of the test lamp. The color
acceptability is defined as the ratio of St to Sr, i.e. St/Sr. The
color acceptability of higher than 1.0 means that the test lamp in
accordance with the invention produces light of more saturated
chroma than the reference source of light.
B. For lamps giving a color temperature of 2,500.degree.K and
having a constant interelectrode gap length and a constant lamp
input of 400 watts, the relation between the lamp diameter and the
luminous efficacy is shown in FIG. 3, that is, luminous efficacy
increases with an decreasing arc tube diameter. Accordingly, it is
preferable to adopt a diameter d not larger than 13 mm from the
viewpoint of the lamp efficiency, because a considerable reduction
of the efficiency is brought about with a diameter d above 13 mm.
In combination with the condition (I), the diameter d must be given
in the range 9<d.ltoreq.13.
C. For lamps giving a color temperature of 2,500.degree.K and
having a constant arc tube diameter, the relation between the
luminous efficacy and the lamp wattage per unit length of the
interelectrode gap length (i.e. the lamp wattage W divided by the
interelectrode gap length) is illustrated in FIG. 4. In this case
the lamp wattage W is so designed as to be kept constant.
Therefore, as seen from FIG. 4, luminous efficacy increases with
decreasing gap length, that is, increasing the lamp wattage per
unit length. On the basis of a series of curves in FIG. 4 for lamps
having the same color temperature of 2,500.degree.K but different
arc tube diameters, lamp wattages per unit length W.sub.e
(watts/cm) with which luminous efficacy of more than 60 lumens/watt
is attained, are approximately given by the expression
W.sub.e .gtoreq.13.3d - 76.4 (IV)
which corresponds to the region a in FIG. 5.
D. On the other hand, the increase in the lamp wattage per unit
length of the interelectrode gap length in excess of a certain
limiting level is accompanied by a relatively large lumen decrement
of the lamp and the increase in the lamp voltage during life, which
are due to the accelerated reaction between the sodium and the
alumina envelope. As a result of a series of life tests performed
by the inventors, such a limiting value, here referred to as
W.sub.p, for lamps with different lamp diameters is approximated by
the relation
W.sub.p = 16d - 58 (V),
where W.sub.p is in watts per centimeter unit, i.e. watts/cm, which
corresponds to the curve b in FIG. 5. The limiting value W.sub.p
corresponds to those lamp wattages per unit length which secure
lumen maintenance of more than 70 percent and keep the increase in
lamp voltage within 15 percent of initial value in around 6,000
hours.
By the harmonic combination of the results (A) through (D) as
described above an electric discharge lamp can be provided which
attains the object of the invention. The process of deriving the
essential conditions for a lamp satisfying the object of the
invention, is now described in the following.
In order to get a good color rendition and obtain good performance
characteristics, from the formula (I) it should follow that
25.gtoreq.E.gtoreq.37.7 - 2.05d (but, d>9)
From the stand point of lamp wattage, the luminous efficacy and the
life performance of the lamp should be taken into consideration so
that the above relation (IV) and (V) must hold.
Namely, from the relation (V) it follows that ##EQU3## which is
identical with the relation (II) as mentioned before. Moreover, it
follows from the relation (IV) that ##EQU4## which is equivalent to
the relation (III) mentioned before.
As has hitherto been described, in order to realize a high pressure
metal vapor discharge lamp having a high luminous efficiency, a
good life performance, and color acceptability of higher than 1.0,
the lamp should be so designed that the above given relations (I),
(II), and (III) may be simultaneously satisfied.
When the discharge lamp is operated together with a ballast, it is
desired to use a ballast of lower power loss, lighter weight and
lower cost. Accordingly a lower operating voltage of the discharge
lamp is desired which can cooperate with such an economical ballast
as described former. As one example, it is noted that the operating
voltage of the discharge lamps needs to become not higher than 180
volts for use with usual ballasts whose secondary voltage must not
exceed 300 volts according to the Regulations for Japanese
Electrical Manufactured Articles. The condition which makes it
possible to operate the lamp together with such an economical
ballast at such a relatively low open voltage, can be obtained
through the modification of the formula (I). Namely, it follows
that ##EQU5## where V.sub.LO is the value in volts of a critical
lamp voltage, below which the economical lamp ballast can be
designed.
The most economical ballast is a single choke one, which is usually
used for popular high pressure vapor discharge lamps.
In order to utilize a choke ballast for the lamp made in accordance
with the invention, V.sub.LO should be taken to be about 60 percent
of the supply voltage Vs. Namely, the formula (IV) might be again
modifieid as follows: ##EQU6##
Here if the power supply line has a voltage of 230 V or 240 V, then
##EQU7##
If the line voltage of the power supply is 220 V, ##EQU8##
Further, if the line voltage of the power supply is either one of
220 V, 230 V and 240 V. Vs in the formula (VII) may be taken to be
the minimum value of 220, then, ##EQU9##
As is apparent from the above description, a promising high
pressure sodium lamp from the lamp characteristics and economic
point of view cannot be provided without satisfying the relation
(VI), especially (VII) except (II) and (III).
The features of the invention believed to be novel will be more
particularly pointed out in the appended claims.
* * * * *