Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
PHN. 7635C.
~0;~8922
m e invention relates to low-pressure gas dis-
charge lamps.
In order to cbtain more radiation from such
lamps, it is known to increase the la~p power by in-
creasing the lamp current. A detriment~l result there-
of is that when increasing the power to more than a given
value more useful radiation is generated, but the co~ver~
sion efficiency of the electrical energy supplied to the
lamp into this useful radiation decreases. In addition
the los æs in a stabilizing element æ ries-arranged with
the la~p, for example, a choke or resistor increase when
the current intensity increases.
A known method of inhibiting the above mentioned
detriment 1 effect is to enlarge the surfa oe of the wall,
for example, by indentation as is described in U.S. Patent
Specification 2,950,410,which issued on August 23, 1960 to
Gbneral Electric Oo. m e drawback of these lamps is t~eir
oo~plicated and oonsequently expensive manufacture, and
moreover the inp~wf~ent achieved is only little. Further-
more the light output decrea æ s in the long run because
dust may oollect in the grooves on the outer side of the
lamp.
Another embcdiment is known from U.S. Patent
Specification 3,290,538, which issued on December 6, 1966
to Westinghouse Electric Cbmpany in which a low-pressure
mercury vapour discharge lamp is described which is provided
~ - .
; - 2 - ~
~ .
P]~N 7635C
1,7.75
~0389Z2
with an inner tube. Also in this case the improvement
in the increase of the light output in case of an in-
creasing load is only little when it is compared with
the same discharge lamp without an inner tube.
In a low-pressure gas discharge lamp accord- -
ing to the invention a solid state body having a struc-
ture permeable to the gas discharge is present in the
space between the electrodes; this lamp is sharacteriz-
ed in that the body is present over at least half the
electrode distance and is thinly distributed over
the discharge space, the ratio between the volume
of the body and the volume of the discharge space be-
ing between 3.10 7f/ ~ and 3.10 f/~ in which f re-
pres~nts the quotient of the volume and the area of
said body in microns and ~ is equal to 5 microns.
The electrode distance is ~nderstood to
mean the distance between the electrodes measured
along the axis of the discharge space.
The effect of the presence of said body,
which need not consist of one uninterrupted assembly,
in the discharge space is that for the same current
intensity through the lamp the lamp voltage can be
considerably increased, while the detrimental ef~ects
which in the above-mentioned known lamps are accompa-
nied by an increase of the lamp power due to an increase
o~ the lamp current occur to a much lesser extent.-This
does not only apply to lamps according to the said pa-
-
''- `~:
~- . .
PHN. 7635C.
10389Z2
tent specifications but also to an even greater extent
to normal lamps.
In addition, as ccmpared with lamps without
the said body the losses at the electrodes and the
losses in the stabilizing element are less at the -~
same lamp power due to the lower lamp current required. ~ ~.
This mEans that without an increase of the energy con-
sumption by the lamp and the stabilizing element the
light output per unit vDlume of the lamp can be oon- " --
siderably increased.
It is known from French Patent Specification ~-
1,026,044, which issued on April 22, 1953 to Atelier de
Constructions electriques de Charleroi, to provide ;
bodies of, for exa~ple, glass or metal between the elec-
trodes in a low-pressure mErcury vapour discharge lamp ~ -
having a luminescent wall so as to increase the light
output per unit valume of the lamp. ~hese bodies may
have the shape of discs, tu~es, helixes or may consist of
glass wool.
Although the object of this French Patent ~-
Specification is to increase the light output per
unit volume, as stated above, it is not stated which
conditions, p æ ticularly the quantity and the dis-
tribution of the material of the bodies must be -
satisfied to realize this increase. In case of a too
dense packing of the bcdies no stable discharge can
build up; on the other hand a too thin structure of
the bodies will not have a noti oeable effect.
.L4 ~..
PHN 7G35C
1.7.75
.
10389Z2
There is of course a relationship between
the area of the body and its shape. This relationship
becomes manifest in the shape factor f denoting the
relationship between the area and the volume of the
body.
Eminent results are obtained when using a
ratio between the volume of the body and the volume
of the discharge space between 3.10 f/ ~ and
- 3~10-3f/ ~ ,
It is not necessary that the body having a
thin structure is present over the entire distance
between the electrodes in the discharge space; in or-
der to obtain a regular distribution of radiation it
is generally desirable for the body to be present
over at least 80% of this distance.
If the above mentioned conditions-are satis-
~ fied and if the material is substantially homogeneous-
ly distributed it is found that, independent of the
material used, as an average per-cubic mm of the
volume of that part of the discharge space where
the body is present a quantity of between 5.10 mg
and 5.10 3 mg of the body i9 present.
In a preferred embodiment of a lamp accord-
ing to the invention the electrode distance divided
by the average diameter of the cross-section of the
discharge space perpendicular to the discharge axis
is greater than five. The process of producing radiation
.
. l']~N 76~5(,
, . 1.7.75
.......
103892Z
in the discharge space then proceeds in the most favour-
able way,
In,another preferred embodiment of a lamp
according to the invention the density of the thin-
structured body near the longitudinal axis of the dis-
charge space deviates from that near the wall. It may
therefore be advantageous for a lamp according to the
invention~ to choose in the discharge space à smaller
density of the thin-structured body near the longitu-
dinal axis of the discharge space than near the wall.
As a result the risk of an uneven temperature distribution
on the wall is reduced; such an uneven temperature dis-
~ibution gives rise to morcury deposits on the colder - ~ .
parts of the luminescent material in low-pressure mer~
- cury vapour discharge lamps, having a luminescent coat-
ing and to the formation of sodium mirrors on colder
. spots in low-pressure sodium vapour discharge lamps.
On the other hand, to obtain a highest possible light
.' ' output it may be advantageous, for example in the case
of a circle-cylindrieal discharge space to render the
density of the thin,-structured body near the longitu-
- dinal axis of the discharge space groater than near
, the wall.
. . A practical reaiization of a thin body in
., 25 a lamp according to the invention may consist of fila-
'~, ment wool, such as glass wool, for example, quartz
'', glass wool or metal wool, for example tungsten wool.
~ , .
. .
. . .
, . ~ . . , . - :.
:,;. - - .. - ' : ;
. .: - , . : .-. . . , .: , .. . . .
~JIN 7~)35C
1.7.75
.. ' ' ' ' . ' .
10389ZZ
In a special-embodiment of a lamp according to the in~
vention the metal wool is provided with an electrical
insulating material, so that a favourable potential
distribution over the thin-structured body may be
obtained. The average wire diameter is preferably
chosen to be between 5/um and 100/um because a suf-
ficiently thin structure is then obtained between the
limits as mentioned above.
~n a special embodiment of a discharge lamp
according to the invention the thin-structured body
may be luminescent, for example, it may consist of a
luminescent glass or of glass coated with luminescent
material such as manganese and/or antimony-activated
calcium halophosphate.
The radiation output of a lamp according to
the invention is very high if the thin-structured
body has a low absorption for the useful radiation
which may be both in the visible and in the ultra-
violet part of the spectrum. This mày be achieved
when the material of the body is chosen to be such
that this useful radiation is satisfactorily passed
or reflected. If the material itself has a too strong
absorption, a surface coating may be provided on which
reflection may occur. This coating may consist of,
for example, zirconium oxide, magnesium oxide, or
barium sulfate.
Partlcularly in the case of small dimensions
.
. ~ 7
, . .
P~IN 7G~5C
1.7.75
10389ZZ
the temperature of the discharge space may reach such
a value that the critical vapour pressure for the op~
timum conversion of electrical energy into useful ra-
diation is exceeded. The conversion efficiency may in
these cases be increased by using known means, for
example, cooling of the entire lamp or part thereof,
for example, by providing radiation shields on the
electrode stems; another means to achieve this object
is to provide an alloy regulating the vapour pressure
in the discharge space. In a low-pressure mercury
vapour discharge lamp the use of an amalgam of mer-
cury and indium is possible.
The invention may be used for the most wide,-
ly divergent types of low-pressure gas discharge lamps;
typical examples are low-pressure sodium vapour discharge
lamps and low-pressure mercury vapour discharge lamps
provided or not provided with a luminescent coating.
Since the radiation output per unit volume
; is very large, lamps according to the invention can
be very satisfactorily used for reproduction purposes.
The lamps may then be formed, for example, as so-called
- aperture lamps through which a very strong directed
beam of light is obtained. On the other hand it is
possible to make very compact fluorescent lamps hav-
~ing a high light output from a small total volume.
It is of course desirable that the material
of the body during manufacture and during the lifetime
PIIN 7G35c
1 . 7 . 75
103892Z
of the lamp is not disturbing. Consequently, materials
are preferably chosen whIch emit as little gas as pos-
sible, which are not decomposed and cannot be attacked
by the gas discharge. Since the gas discharge in a low-
pressure sodium vapour discharge lamp is very agressive,-
it is desirable that the thin-structured body in such
lamps is sodium resistant; particularly a body consist-
ing of or coated with gehlenite glass is suitable for
this purpose.
The invention will now be described with
reference to a drawing and some examples.
Fig. 1 is a diagrammatical cross-section of
a low-pressure mercury vapour discharge lamp according
to the invention, provided with a luminescent coating.
- Fig. 2 shows an embodiment of a low-pressure
mercury vapour discharge lamp for emitting ultraviolet
radiation in which the filling body does not consist
of one uninterrupted assembly. .
Fig. 3 shows a U-shaped curved embodiment
of a low-pressure mercury vapour discharge lamp ac-
cording to the invention.
Fig. 4 shows an embodiment of a low-pres-
sure sodium vapour discharge lamp according to the
invention.
; 25 The lamp of Fig. 1 has a glass envelope 1
provided with a luminescent coating 2 which may con- ~ ~ -
sist of, for example, manganese and/or antimony- ~-
.- . , :
- ' '. ,:
- 9
' '
- ~lIN 7G35
1.7.75
~0389ZZ
activated calcium halophosphate. The lamp is filled
with mercury vapour and a rare gas or a combination
of rare gases. Thermally emittin~ electrodes 3 and 1
are provided at the ends of the discharge space. The
discharge space accommodates over substantially the
entire space a body 5 consisting of thinly packed
- quartz glass wool.
The lamp in the embodiment according to
Fig.- 2~ likewise as the lamp according to Fig. 1,
contains thinly packed glass wool denoted by 6. The
glass wool 6 does not constitute an uninterrupted
body, but is distributed over three packets 7, 8 and
9. Between these packets and between the packe~s and
the electrodes there are spaces not accommodating
glass wool. The sum of the lengths of the packets
measured along the discharge axis is larger than half
the distance between the electrodes, namely approxima-
tely ~8% of this distance.
; Fig. 3 shows a modification of the lamp
according to Fig. 1 in which the discharge tuba is
curved to a U-shape.
The lamp according to Fig. 4 has a U-shaped
discharge tube 10 surrounded by an outer envelope 13.
Thcrmally emitting electrodes 11 and 12 are provide~d
at the ends of the discharge space. The discharge
space accommodates over substantially its entire
space a body 15 consisting of thinly packed
. . .
-- 10 _ ,,
, . . . ' . -:
: : ::
. . ~ : . . . . . .
- P~IN 7G35c
1.7.75
103~9ZZ
gehlenite glass wool.
A number of measurements were performed on
a 40 W low-pressure mercury vapour discharge lamp
according to Fig. 1; the results are shown in table
I. The lamp is filled with 58 mg of quartz wool hav-
ing a thickness of 10/um and comprises mercury and
neon at a pressure of 1 torr.
TABLE I
electrode distance (cm) 55
diameter (cm) 3.6
current intensity (mA) 300-
light output (lumens) 2520
efficiency lamp (lumens/watt) 63
-' efficiency lamp +
stabilizing element (lm/W) 55
For the lamp there applies that the ratio between
the volume of the body and the volume of the discharge
space is 7x10 5f/~ . As an average per cubic mm of the
volume 10 mg is present.
A number of measurement# were performed on a
40 W low p--essure mercury vapour discharge lamp accord-
ng to Fig. 1 and on a fcw lal~ps without a fill~ng body
, - 1i - ' . :
.' ' ' . "''.
- . '
~ .. , . . . . . , : . , ~ . .
PlIN 7()35C
1-7-75
.
.. ' . ' '.
- 10389ZZ
5 but having the same structure; the results for the
different lamps are shown in Table II. In this Table
the light output and the efficiency of a discharge
lamp according to the invention filled with 140 mg of
wool of glass having a composition in percentage by
; weight of: 68.7~ of SiO2; 2.95% of B203; 9.1% of NazO;
- 10.85~ of K20; 6.85~ of BaO; 1.5~ of Al203 and 0.05%
- of SrO and having a thickness of 36/u are compared with
the corresponding values of a discharge lamp without
; 10 glass wool. Both lamps contain mercury and a mixture
of 75~ by volume of argon and 25~ by volume of neon at
a pressure of 2,5 torr.
.
TABLE II
-- with 140 mgwithout
glass woolglass wool
~ ~1
e]octrode distance (cm) 55 55
diameter (cm) 3.6 3.6
current intensity (m~) 400 900
light output (lumen) 3000 2200
light output per cubic cm 5.4 3.9
efficiency lamp (lm/w) 75 55
efficiency lamp +
stabilizing element (lm/w) 62.5 37
- 12
- ' . ' ': '
.
I'IIN 7~)35
1.7~15
10389Z2
This Table shows that the light output per
unit volume of a low-pressure mercury vapour discharge
lamp according to the invention is larger than that of
such a lamp without glass wool.
The Table also shows that the efficiency of
the lamp has considerably increased. Furthermore it
is found that the efficiency of the lamp in series
with the required stabilizing element has increased
by nearly 60~. This also resides in the fact that the
current intensity has become considerably lower so
that considerably fewer losses occur in the stabiliz-
ing element and on the electrodes.
-The ratio between the volume of the body and
the ~olume of the discharge space is 9.6 x 10 5f/ A ~
for this lamp. As an average per cubic mm of the volume
2.5 x 10 4mg is present. -
Table III shows'some measuring results of
two similar 20 W low pressure mercury vapour discharge
lamps with and without filling body 5. In this Table
the light output and the efficiency of a discharge
lamp according to the invention filled with 20 mg of
- glass
quartz/wool having a thickness o~ 10/u are compared
with the corresponding values of a discharge lamp with-
out quartz/~g~rool. ~oth lamps contain mercury and a
mixture of 72~ by volume of neon and 28~ by volume of
helium at a pressure of 6 torr.
,' ' ,
:' . ~
- :. ! . - ":-... .: ~ ~ .
P~IN 7G~ ~c
1.7.75
10389ZZ
TABLE III
Wit}l 20mg without
quartz glass quartz glass
wool wool
electrode distance (cm) 20 20
diameter (cm) 2.5 2.5
operating voltage (volt) 130 65
current intensity (mA) 200 400
]ight output (lumen) 960 580
light output per cubic cm 9.8 5.9
efficie~cy lamp (lm/W) - 48 29
efficiency lamp + ~,
stabilizing element (lm/w) 40 20
This Table shows that the efficiency of the
lamp in series with the required stabilizing element
is doubled.
The ratio between the volume of the body and
the volume of the discharge space is 1.5 x 10 f/
As an average per cubic mm of the volume 2 x 10 mg
is present.
In the case of a U-shape (see ~'ig. 3) a -
lamp is obtained having approximately the same dimen-
sions as an incandescent lamp which requires a power
of approximately 75 W for the samc light output.
.
j _ 14
.
- . : ~
- PlIN ~G35c
1.7.75
10389ZZ
Table IV shows some measuring results of
two similar 20 W low-pressure mercury vapour discharge
lamps having a luminescent coating with and without
filling body. The lamp according to the invention is
filled with 96 mg of tungsten wool having a thickness
of 15/um. Both lamps contain mercury and a m:ixture
of 72 ~ by volume of neon and 28~ by volume of helium
at a pressure of 4 torr.
TABLE IV
, ' '
with 96 mg without
tungsten wooltungsten wool
electrode distance (cm) 20 20
diameter (cmj 2.5
operating voltage (volt) 120 65
current intensity (mA) 200 400
light output (lumens) 600 580
light output per cubic cm 6.1 5.9
efficiency lamp (lm/W) 30 29
efficiency lamp ~ stabilizing
element (lm/W) 25 20
This Table shows that the efficiency of the
lamp with tungsten wool in series with the required
`~ ' ' ~ .,
I - 15
PHN. 7635C.
103892Z
stabilizing element is 25% higher.
The ratio between the volume of the body and
the volume of the discharge spa oe is 6.6 x 10 5f/A
for this Lamp; as an average per c~bic mm of the volume
9.8 x 10 4 mg is present.
Table V shows some measuring results for a
lcw-pres Æ e sodium vapour discharge lamp according to -
the invention (see Fig. 4) having a power of 35 W in a
U-shaped discharge tube within an outer envelope. 110 mg -
;~,~, .
of gehlenite glass wool resistant to the action of sodium ` ,c
(see United Xingdom Patent Specification 1,204,670 which -
issu~d on Sept~mber 9, 1970 to Philips'Electronic
Industries) having a thickness of 15 /um is present in the
discharge spac~. m e results are compared with a lcw-
pressure sodium vapour discharge lamp without a filling
body, but of the same structure.
," '
' :
~, .
- 16 -
... , ~ .- ,, . : : ,
- - . . -
- I'JIN 7~>35C
1.7.75
103892Z
TABLE V
with 110 mg without
gehlenite gehlenite
glass wool glass wool
electrode distance (cm) 43 43
diameter (cm~ . 1.50 1.50 . ~.
operating voltage (v~lt) 149 70 -~
current intensity (mA) 300 600
light output (lumens) 5250 4450
light output per cubic cm 70 59 : ~
- efficiency lamp (lm/W) 150 127 ~ ~ :
efficiency lamp + stabilizing
element (lm/Watt) 107 78 .
~; .
This Table shows that the light output per
unit vQlume of a low-pressure sodium vapour discharge
lamp according to the invention is larger than of such . :
a lamp with the same power, but without gehlenite wool.
The Table also shows that the efficiency of
the lamp has increased. ~urthermore the efficiency .Vf
the lamp in series with the required stabilizing ele-
.~ - ment is found to have improved by 37~. This also resides
n ' . in the fact that the current intensity has become con-
"~ siderably lower.
. ' The ratio between the volume of the body and
.~ ' , . - 17
.
~N 7G35C
1.7.75
~ 892Z
the vo7ume of the discharge space is 7.6 x 10 f/A
for this lamp. As an average per cublc mm 1.25 x 10 3 mg
is present. '
The lamps provided with a thin-structured body
whose data are shown in the Tables I to V are provided
with the thermionic electrodes which are commonly used
for low pressure mercury vapour discharge lamps and for
low pressure sodium vapour discharge lamps. A favour-
able ratio can then be obtained in a simple manner be-
tween the useful electric power supplied to the lamp
and the losses in the power supply apparatus when the
ratio V/l ~ 7 where V is the operating voltage
in volts and l the electrode distance in centimetres.
.
" ~ ' .
,
_ 18
. . .
. ~Ar . . ~ I
s
