Note: Descriptions are shown in the official language in which they were submitted.
~L2Z~;313l5
PEIN 11 485 l 17-2-1986
"High-pressure mercury vapour discharge lamp".
The invention relates to a high-pressure mercury
vapour discharge lamp having a given power consumption
during operation, provided with a discharge vessel having
a wall of gas-tight, radiation transmitting ceramic
material, said discharge vessel enveloping a discharge
space and being provided with an ionizable filling com-
prising a rare gas, mercury, sodium halide and thallium
halide, an electrode being disposed within said discharge
vessel in the proximity of each of two end wall parts,
the electrode tips facing each other being locat~d at
a mutual distance EA.
A lamp of this type is known, for example, from
rJnited States Patent Specification 3,363,133 showing a
discharge vessel of ceramic material, namely densely
si:ntered polycrystalline aluminium oxide. In addition to
mercury and a halogen, the known lamp comprises one or
more metals such as thallium and furthermore i~ may
comprise an alkali metal, for example, sodium.
The addition of metal haLides, in most cases
~20~ metal iodides, to the ionisable filling of a high-pressure
; ~mercury vapour d scharge lamp is a step that has been used
for quite some time in lamps havin~ a quartz glass dischar-
ge vesselO Its object is to obtain a higher density of
metal~at~ms in the discharge space by utilizing the greater
25~ volatility of the metal halides~as compared wit~ th~t of
; the metals themselves, and hence a areater contribution
of the metals to ~e radiation emitted by the lamp. This
~results in an improvement of the relative luminous flux
and parti~ularly also the colour renditlon of the~lamp.
Alkali metals such as sodium and lithium are used in a
halide form because these metals themselves are too
aggressive relative to the quartz glass wall of the dischar-
:~ ,
~ ~ ge vessel.
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PHN 11 ~85 -2- 17-~2-19~6
In lamps conta:i.ning metal halc1e -the hali~e
pressure is cletermined by the temperature of th~ coldest
spot Tlcp wi-thin the discharge v~ssel. The maximum admlsslbLe
value of T~cp is limi-ted by the material of the discharge
vessel. In -the case oE quartz glass discharge vessels
Tkp may not be more than approximately 800C. It has al-
ready been recognlzed at an early stage that the use
of materials for the wall of ~e discharge vessel which can
be subjected to a hlgher thermal load may lead to higher
hallde pressures. Unlted States Patent Specification
3,234,421 already states the possibility ~ using densely
sintered aluminium oxide as a material for the discharge
vesselO
A halide filling which is frequently used in quartz
glass lamps consi~s of the halides of thallium and sodium
to which mostly indium halide is added. Experiments have
shown that as compared with the quartz glass lamps an im-
provement is o~tained concerning the relative luminous
flux and also to a very slight extent the colour rendition
if such a filling is used in a ceramic lamp vessel as
stated in the above-mentioned United States Patent
Specification 3,363,133. Such a lamp has, however, some
great drawbacks, so that its practical use is not very
well possible. In the first place the colour rendition is
still insufficient for many uses and furthermore these lamps
have among themselves a strong spread in their colour
point and a variation thereof during their lifetime.
Secondly it is found that the colour point of these lamps
is greatly dependent on variations in the power consumption
~30 of the lamp. These variations are the result of malns volt-
age variations that cannot be avoided in practice.
Vnited States Patent Specification 3,334,261
mentions lamp fillings comprising halides of;rare earth
metals. It has been found that lamps having a satisfactory
colour rendition are possible particularly with Dy, Ho,
Er, Tm and/or La. A drawback of these lamps is that they
have a high colour temperature (4000 K or higher). For
practical uses a lower colour temperature is often very
.
~i3~
PHN 11 485 -3- 17-2-1986
much desired. IE the colour temperature in -these lamps is
to be decrea~ed, the use of sod:lum hali.de ls generally
required which must be used in comparative].y larcJc quanti-
ties~ This resul-ts in a great decrease o~ the contribution
of the rare earth metals to the radiation emitted by the
lamp so that the colour rendition of the lamp is adversely
affected.
It is an object of the invention to provide lamps
with which hoth a high relative luminous flux and a satis-
factory colour rendition are obtained in the low range ofcolour temperatures (approximate].y 2600-4000 K).
According to the invention a lamp of the type
described in the opening paragraph is characterized in
that the wall load, defined as the quotient of power
consumption and outer surface area of the part of the wall
of the discharge vesse]. located between the electrode
tips, has a value of at least 25 W/cm2, in that the ratio
between the effective internal di.ameter ID of the discharge
vessel and EA has a value in the range of 0.4 ~ ID/EA C 0.9,
ID heing defined as the square root of the quotient of the
volume of the discharge space between the electrode
tips and EA, and in that the ratio between the largest
internal diameter ~if the discharge vessel and EA is at
most equal to 1.1.
25 : : The invention is based on the recognition of the
: fact that a satisfactory colour rendition~is possib].e when
sodium halide is used in the filIing of a lamp if during
;~ : operation of the lamp there is a strong broadening and
reversal of the emission of the sodium in the Na-D lines
which:are located at 589.0 and 589.6 nm at ve.ry low
: partial Na-pressures. By broadening and reversal the Na-D
lines~assume the shape of emission bands, the short-wave
: band being shifted to shorter wavelengths:and the :
long-wave band being shifted to longer wavelengths as the
emission is more reversed. A measure of the reversal is
therefore the distance ~ ~ in nm between ~he maximum
~:~ values of the Na-emi.ssion bands. The long-wave emission
~ : band of the Na i9 shifted to the red part of the spectrum~
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~G~3 !3
PHN 11 ~85 -~- 17~-19~6
which is very favourable for the col.our rendition proper-
ties. It has been found that a better colour rencli,tion,
that is to say, a h.~gl1er val.ue oE -the average colour
renderi,ng :Lnclex Ra8 ls obtai.ned as ~ ~ has a higher value.
The colour rendering inclex Eor deep red colours, ~9, which
is often negative to deeply negative in di,scharge lamps
may assume positive values in lamps according to the
inventi,on if ~ ~ is relati.vely high. The value of ~A at
which given colour rendition properties are obtained is
still dependent on the lamp type and the lamp filling. Thus,
in lamps having a low power consumption (for example, less
than 100 W) lower values of ~ ~ may generally suffice to
obtain the same colour rendition properties as in lamps
having a higher power consumption, because a higher mercury
pressure prevails in these low-power lamps so that an
increasing Van der Waals broadening is an extra contri-
bution, predominantly to the long~wave side of the Na-D
lines.
It has been found that two conditions are to be
: 20 fulfilled for a strong broadening and reversal of the Na-D
: l.ines. In the first place a large contribution of Na-D
emission is required. This involves a high sodium halide
pressure and hence a high temperature of the coldest spot
: Tkp in the discharge vessel, for example, 300C or more.
This requirement for Tkp e~cludes the use of quartz glass
for the discharge vessel. In a lamp according to the
invention a gas-tight, radiation transmitting ceramic
material is therefore used for the wall of the discharge
vessel. A very suitable material is aluminium o~ide which is
3~ usable in a densely sintered polycrystalline form and
a].so in a monocrystalline form (sapphire). Other possible
materials are, for example, densely sintered yttrium oxide
and yttrium aluminium garnet. The said high values of
Tkp are attained in a lamp according to the invention by
: ~ 35 dimensioning the discharge vessel for a given power
consumption during operation in such a manner that the wall
load has a value of at least 25 W/cm . The wall load is
defined as the quotient of power consumption and surface
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PHN 11 485 -5- 18-2~1986
area oE the discharge vessel, cons.Lder:Lng only ~.hat part of
the outer surface area of the discharge vessel that is
loca-ted between the electrode tips.
The second conditi.on which is to be fulfilled to
obtain a sufficiently high ~ ~ is that the actual discharge
arc in the discharge vessel is to ke surrounded with a
sufficiently thick layer of Na-atoms in the fundamental
state. I`his means that the discharge vesse]. must fulfil
given geometrical requirements, notably a relatively wi.de
discharge vessel is necessary. In a lamp according to the
invention the ratio between the effective internal diameter
ID of the discharge vessel and the electrode distance EA
has a value in the range of 0,.4 ~ ID/EA ~ O.9. ID is
herein understood to mean the square root of the quotient
of the volume of the discharge space between the electrode
tips and EA. It has been found that also in ].amps having a
discharge vessel deviating from the cylindrical shape a
thick shell of Na-atoms in the fundamental stat.e is formed
around the discharge arc such that a strong reversal of the
Na-D lines i5 possible if the ahove-rnentioned condition
of ID/EA is fulfilled. A lamp as shown in the United
States Patent Specification 3,363,133 already referred
t.o above ~has ah ID/EA value of approximate~y~.0~,25. It has
: ~ been found that for ID/EA values of less than 0.4 a :
too small ~ ~ is obtained and therefore a too low Ra8
: value. ID/EA values of more than 0.9 are not used be-
cause at such values Tkp easily assumes a too low value.
Experiments have also shown that a further condition is to
be imposed as regards the largest internal. diameter 0i :
~: 30 for Iamps having a strongly curved wall surface o~ the
: discharge vessel, far example, ellipsoidal, spherical or
approximately spherical lamp vessels. In fact, the ratio
between 0i and EA must be not more than 1.1 because~a too
low Tkp is obtained: at higher values, even if the con-
dition for ID/EA is satisfied. For cylindrical discharge
: vessels ID is substantially equa:l to 0.89 0i so that the
condition for 0i/EA is always satisfied if the con-
dition for ID/EA lS satisfied.
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~;3~.3~
PE-IN l1 ~85 6- 17-2-19~6
In a preferred embodiment ,llof a lamp accordi.ng to
the invention the distance between the electrode -tips
and the adjacent end wall parts of the discharge vessel
is not more ~han hal:E the largest internal diameter
(~0i) In that case the required high value of the tempera-
ture of the co].dest spot in the lamp can more easily be
attained, generally also without extra steps for heat
insu].ation of the lamp extremiti.es.
The lamps according to the invention have the
advantage that for agiven filling they have only a little
spread in the colour point of the emitted radiation and
also a very sma].l variation of the colour point during
their lifetime. A great advantage of these lamps is that
they do not substantially show any colour variation when
varying the supplied power within fairly ample limits. It
has been found that the effects of variations in the power
counteract each other, in a sense, as a result of the
relatively high sodium pressure and the lamp geometry
used, so that a colour point st.abilisation is obtained.
For the quantity of mercury which is used in the
lamps according to the invention considera-tions apply that
are analogous to the known metal halide-containing high-
pressure mercury vapour discharge lamps. Generally the
mercury quantity is mainly determined by t~e arc voltage
desired in the lamp. The mercury quantity will fre~uen~ly
: be relatively low for lamps having a high power (for
; ~ example at least 1 mg per cm3 o the discharge space at
powers of the order of 2000 W) and will increase with a
decreasing power (to, for example 100 mg per cm at powers
of the order of 10 W~.
The filling of the lamps according to the in-
vention comprises halides, preferably iodides, of sodium
and of; thallium. The sodium halide is present in~excess,
that is to say, unevaporated sodium halide is still
~ 35 present during operation of the lamp. In practical lamps the
: sodium halide quantity is generally at least 10 /u mol
per cm3 of the discharge space (for lamps having a higher
: ~ power) and assumes larger values as the power decreases
.
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~G3~L3~3
PHN 11 ~85 -7- 17-2-1986
(for example, to 500 /umol per cm3 for the smallest lamps).
In the lamps the thallium halide contributes in the
form of the predominantly green thallium radiation so that
white or substantially white light can be obtained in
combination with the sodium radiation. Lamps are preferred
which are characterized in that the molar ratio between
thallium halide and sodium halide is at least 0.05
and at most 0.25. The lamps according to this pEeferred
embodiment emit light at a comparati.vely low colour tempera-
ture, which is very much desirable for certain uses(for example, lighting for the living room and decorative
lighting). The colour temperature is dependent on the
Tl:Na ratio chosen and has values of approximately 2500 K
(colour point slightl~ below the line of the black radiators
and h.aving a slightly yellow colour aspect) to approximately
3000 K (colour point slightly above the line of the klack
radiators and having a slightly green colour aspect). Lamps
having a colour pcint which is substantially on the line
of the black radiat.ors have a colour temperature of approxi-
mately 2700 K.
A further advantageous embodiment of a lamp accord-
ing to the invention is characterized in that the discharge
vessel further comprises at least one halide of a metal
radiating substantially in the blue or purple part of the
spectrumr which halide, compared with sodium halide, has
a hi~h volatility ~nd i.n which the molar ratio between
th~ halide and the halides of Na and Tl combined has a val.ue
of up to 0.1 at a maximum. The use of blue or purple
radiators provides the possibility of obtaining lamps hav-
ing a higher colour temperature of the emitted radiation(higher than approximately 2700 K). To maintain sat.isfa tory
colour rendition properties, it is required for the halide
of the blue or purple radiator to be used in relatively
small quantities because otherwise the sodium halide is too
much diluted so that ~ ~ would be adversely affected.
Therefore volatile halides are chosen (saturated vapour
pressure at 900C at least. a factor of 10 larger than
that of sodium iodide) in which the molar ratio between
these halides and the halide of Na and Tl combined is not
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~3~3~
Pl-IN 11 ~85 -~- 17-2-1986
more than 0.1 and preferably of the order of 0.01. In
this manner lamps can be obtained havlng a hicJh e~ficlency,
a satisfactory colour rendition and a colour -temperature
of up to approxima-tely 3200 K. Lamps of this type are
preferred which comprise at least one halide of at least
one of the elements In, Sn and Cd because the best results
are achieved with these halides.
A further preferred embodiment of a lamp accord-
ing to the invention is characterized in that the di~charge
vessel also comprises at least one halide of at least one
of the elements Sc, La and the lanthanides, in which the
molar ratio between these halides and the halides of
Na and Tl combined has a value of at least 0.02. The said
elements Sc, La and the lanthanides have an emission
consisting of many lines distributed over the entire
spectrum with the centre generally being in the blue part
of the spectrum so that these elements, if used only in
a lamp, yield a colour point of the emitted radiation of
5000 K. Consequently, with the lamps of this embodiment
as compared with the lamps comprising only Na and Tl
higher colour temperatures can be attained whilst main-
taining high luminous fluxes and very satisactary
colour rendition properties. Values of the molar ratio be-
tween the halides of Sc, La and/or lanthanide and the hali-
des of Na and Tl combined are then chosen to be at least0.02 because then generally colour temperatures are
attained of at least 3000 K. In fact, for colour tempera-
tures of less than 3000 K the embodiments described herein-
before with volatile, blue radiators are found to be
more advantageous. In these lamps having a colour tempera-
ture of 3000 K or more the use of at least one halide of
at least of one of the elements Dy, Tm, Ho Er and La is
preferred. With Dy lamps can be obtained having very high
values of Ra8 and Rg and with colour temperatures of up to
approximately 3600 K. The molar ratio between dysprosium
halide and sodium and thallium halide is then preferably
0.03 or more. With one or more of the elements Tm, Ho, Er
an~ La it is possible to make lamps having colour tempe-
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6~3~;3~3
PHN 11 485 ~9~ 17-2-1986
rat~lres of up to approximately ~500 K, where -the molar
ratlo between the halides of these lanthclnides and the
sodium and -thallium halide is preferably chosen to be
0.04 or more.
Embodiments of lamps according to the ~vention will
now be further described with reference to the accompanying
drawing and a number of measurements.
The drawing shows in a cross-section a high-press-
ure mercury vapour discharge lamp according to the invention,
intended for a power consumption of 160 W.
In the drawing the reference numeral 1 denotes the
discharge vessel of a lamp according to the invention hav-
ing a nominal power of 160 W. The discharge vessel 1 has
a cylindrical wall part 2 of densely sintered polycrystal-
line alumini~lm o~ide having a total length of 19 mm, anexternal diameter of 8.45 mm and an internal diameter of
6 85 mm. End wall parts 3, 4 and 5, 6, likewise of densely
sintered aluminium oxide are sintered in a gas-tight
manner to the respective ends of the part 2. These end
wall parts consist of discs 3 an~ 5 having a thickness
of 2 mm and projecting tubes 4 and 6, respectively. The
projecting portion of the tubes 4~ 6 has a length of 8 mm,
an external diameter of 3 mm and an internal diameter
of 2.05 mm. Tungsten pins 7 and 8 having a diameter
of 0.2 mm are sealed in the tubes 4, 6, respectively, to-
gether with aluminium oxide pack:ing pieces 17 and 18,
;~; respectively with the aid of~ a halide-resistant melting
glass denoted by the reference numerals 9 and 10, respective-
ly. The ends of the pins 7, 8 located inside the discharge
vessel 1 constitute electrodes 11 and 12, respectively,
;~ with the tips 13 and 14 facing each other and are provided
with tungsten electrode filaments 15 and 16, respectively
(2 layers, 5 turns each o~ wire having a diameter of 0.3 mm).
The distance EA between the tips 13 and 14 is 10 mm. The
effective internal diameter~ID of the discharge vessel
1 is 6.07 mm. The ratio ID/EA is therefore 0.6. (The
largest internal diameter ~i is 6.85 mm and thus 0i/EA =
0.685). The dlstance between the electrode tips 13 and 14
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~Z~i3~3~s
PHN 11 485 -10- 17-2--1986
and the ell~ wall parts 3, ~ and 5, 6, respectively, is
2.5 mm. The conten-ts of the vessel I are 0.55 cm3.
For a power oE 160 W the wall load~oE this lamp l~s 60 W/cm~.
The discharge space within the vessel 1 contains an
ionisable filling comprising mercury, argon as an ignition
gas and halides. The discharge vessel 1 of the lamp is
generally built in an outer envelope (not shown in the
drawing).
EXAMPLE 1
A ]amp having a construction as shown in the
drawing was provided with 12 mg of mercury (approximately
21.8 mg Hg per cm3 contents of the discharge vesse])
and argon up to a pressure of 200 mbar. The lamp also con-
tained 9.2 mg of a mixture of sodium iodide and thallium
iodide, with the molar ratio between Na and Tl having a
value of Na:Tl = 92.5:7.5. During operation of the lamp a
relative luminous flux of 93 lm/W was measured at a power
consumption of 160 W. The coordinates of the colour point
of the emitted radiation were x = 0.465 and y = 0O403 and :
the colour temperature T had a value of 2565 K. For the -
average colour rendering index RaB a value of 8~ was found
and for the colour rendering index R9 a value of +20 was
found. The distance between the maximum values of the Na
emission bands, ~ ~ , was found to be 145 nm. Variation
in the power consumption o~the lamp proved to have little
influence on the colour point. At a power of 150 W x was
0.466 and y was 0-404 (Tc = 2560 K) and at a power of
175 W x was 0.464 and y was 0-403 (Tc = 2570 K).
EP~IPLES 2 to 10.
Nine lamps having the same construc~ion as the
lamp of Example 1 were provided with an iodide mixture
which in addition to the iodides-of Na and Tl also contain-
ed an iodide of a blue radia~or (indium, lanthanum or
a lanthanide). Likewise as the lamp of Example 1 these
lamps were provided with 1~ mg of mercury, with the except-
35 ion of Example 2 (10.1 mg Hg) and Example ~ (10 mg Hg).
The following Table states for each Example the total
mass M of the iodide mixture, the blue radiator used
and the molar ratio of the iodides. Furthermore the Table
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~2G3~38
PHN 11 485 -11- l7-2-l986
s-ta-tes for each lamp the results o:~ measurement.s at
a power consump-tion of 150 W. The relative ].urninous :~lux
~ (ln/W), the colour point x,y, the colour temperature
Tc (K), the colour renderin~ indices Ra8 and R9, and the
distance ~ ~ (nm) were measured.
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PHN 11 4 85 -12- 17-2-1 9~S
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PHN 11 485 -13 '17-2-1986
EXAMPLE 1 1
A lamp having a construction as shown in the draw-
ing, but intended for a power of 110 W was manufactured.
The lamp had an external diameter of 6.0 mr~l, a (laryest)
internal diameter of 4.8 mm ~effective internal diameter
ID = 4 . 25 mm~ and an electrode distance EA of 8 mrn. The
ratio ID/EA was therefore 0. 53 . The end wall parts consisted
of a disc having a thickness of 3 mm and a projecting tube
having an external diameter of 3 mm ~length projecting
portion 7 mm). The distance between the electrode tips
and the respective end wall parts was 1. 5 mm. The contents
of the discharge vessel were 0.20 cm3. At a power of 110 W
the wall load was 73 W/cm2. The lamp was provided with 5 mg
of mercury (25 mg Hg per cm3) and argon up to a pressure
f 200 mbarO Furthermore 4.9 grams of a mixture of sodium
iodide and thallium iodide (molar ratio Na:Tl = 92.8:7.2) was
added to the filling. A relative luminous flux ~ = 88 lm/W,
chromaticity coordinates x = 0.444 and y = 0.414, colour
temperature TC = 2970 K, Ra8 = 84, P~g = -19 and A ~ = 91 nm,
were measured on the lamp.
EXAMPLES 12 and 13.
Two lamps having a construction analogous to that
of the lamp shown in the drawing, but intended for a power
consumption of 40 W were manufactured. The external diameter
f these lamps was 4.4 mm, the llargest) internal diameter
was 3.5 mm (ID = 3.1 mm) and the electrode distance
EA was 3.5 mm. The value of ID/EA thus was 0.69. The end
wall parts had a disc having a thickness of 3 mm and a
projecting tube having an external diameter of 2 mm
(le`ngth projecting portion 3 mm). The distance between
electrode tip and end waIl part was 1.25 mm. The contents
of the discharge vessel were 0.0S8 cm3. At a power of 40 W
the wall load was 82 W/cm2. The lamps were provided with
argon up to a pressure of 800 tnbar, with mercury (Example
1 2 : 2.89 mg: Example 13: 3.63 mg), and with a mixture of
iodides of Na, Tl and In. The lamp of Example 12 contained
2 . 4 mg of this mixture in the molar ratio Na:Tl:In =
84.95:14.50:0.54. The lamp of Example 13 contained
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~L2~3~
PHN 11 485 -14- 17-~2-1986
2.74 mg of -this m:Lxture in the molar ratio Na:Tl:In =
80.80:i8.67:0.52. The followlng measurements were made
at a power consumption oE 40 W:
lExampl~ ample 13
~-tlm~/w) r78.5 70
x 1Ø441 10.436
y '0.378 ~0.399
Tc (K) ~2715 !2965
a8 ,89 192
Rg .24 ¦47
~ ~(nm) ,129 ¦141
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