Note: Descriptions are shown in the official language in which they were submitted.
` 1070368
Thi~ invention relates to electrical dischnr~e lampJ and
more especially to hi~h-preRYure diRcharge lamps for oenernl li~htins
purposes. Such diYchar~es operate in an Atmosphere of mercury Yapour
and a small pres~ure of rare ga3 to~ether with the vaporised halide
of at least one other element. ~he rare 8as is only required t~ promote
easy startin~ of the diqcharge.
- High pressure discharges in tin halide ~apour ha~e continuous
cpectra~ with few atomic lines. The~e discharges usually ha~e e~cellent
colour renderin~ properties, and in the caseY of the chloride and bromide
hi~h efficacy~ but their chromaticity coordinates are usually on the
~reen side of the full radiator locus. Discharge~ in mixed halides of tin
ha~e been used to produce a more appealing colour appearance without a
si~nificant los~ of efficacy. The colour appearance is partly determinsd
by the relati~e guantitie~ of chlorin~ and iodine present in the Yapour~
Chemical reactions during the operation of the lamp tend to change the
~apour composition, making it difficult to keep the colour constant.
For many interior lighting purposeq~ it is desirable to have a
dif~erent colour appearance from that obtainable with tin halide dischar~es~
and more particularly a lower correlated colour temperature and chromaticity
coordinates clo~e to ths full radiator locu~.
We have now found that an i~proved high-pressure dischar~e
l~mp can be obtained which operates with the ~apours of onc or more tin
halides and one or more sodium halides, to~ether with mercury and a rare
oAs. In such a lamp hi~hly ~olatile co~plex compounds containin~ both
~odium and tin ~nd the halo~en or halo~ens are formed and produce hi~her
concentrations of sodîum halide and sodium in the arc th~n can be achie~ed
by e~aporation o~ ~odium halid~ alone.
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~07C~368
In accordance with one broad aspect, the invention
relates to an electrical discharge lamp comprising: a sealed
light-transmitting lamp envelope; arc electrodes in said
envelope; and a fill consisting essentially of mercury, rare ~-
gas, tin, sodium and halogen, the amount of tin being 5-100
mol cm 3 and wherein the fill contains 1-250P mol cm 3 sodium
halide such that there is formed at least in operation at least
one volatile complex halide compound of tin and sodium, the
halogen comprising chlorine and iodine or bromine and iodine
and wherein the amount of mercury in the fill exceeds 50~ mol
cm~3
Where the complex halide compound can be prepared and
handled as such, the compound itself can be introduced into the
lamp envelope during manufacture of the lamp. Alternatively
or additionally, however, the elements concerned may be
introduced into the envelope in any convenient form. The
invention thus extends to any discharge lamp containing a fill
of mercury, rare gas, halogen, tin and sodium in appropriate
proportions for the formation of a substantial proportion of
one or more volatile tin sodium halides. Such fills are
exemplified in the practical embodiments described below.
The high-pressure discharge lamps of this invention
overcome some of the colour appearance problems of the tin halide
discharges whilst maintaining or in some cases enhancing the
efficacy of the lamps. It has been found that the properties
of these discharges differ from those in tin halides or sodium
halides, and that they have desirable properties not exhibited
either by tin halide discharges with or without mercury or by
sodium halide discharges alone. At least some of these
properties result from the formation of complex compounds of the
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tin halides and alkali metal halides. One such compound is
NaSnC13, molecules of which can be present in both liquid and ;~
vapor phases. Other complex compounds between tin
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1070368
halides and alkali metal halides also exist. One property of these
complex compounds that is exploited in the present invention is their
high volatility. ~or example, according to vapour pressure data, there
are approximately 2 x 10 ~ cm 3 NaCl molecules in equilibrium with sodium
chloride at 953K (680C). In equilibrium aboYe liquid NaSnC13 at the same
temperature there are approximate;y 10 cm 3 of NaSnC13 molecules. When
NaSnC13 dissociate~ in the di~charge it produces NaCl molecules~ Thus
there are up to 104 timea more NaCl molecules available in the vapour
pha~e and the partial pres~ure of ~odium atoms and sodium-containing
moleculeq is greatly enhanced by this means. To obtain a concentration
of lO cm 3 of NaCl moleculeq by volatilizing NaCl would require a liquid
pool temperature in the re~ion of 1000-1100 C, thus putting a severe rs-
~triction on the choice of arc tube materials. Another desirable property
of the lamps of this invention, which i~ probably associated with the
formation of complex compoundq, is that in some cases the colour appearance
of the discharge is comparatively insensitive to the molar ratio of sodium
halide to tin halide.
Preferred practical embodiments of the invention have a discharge
tube constructed from transparent fused silica, or polycrystalline or single
crystal alumina. The power loading at the wall is in the range 10 -
lOOWcm 2 and the temperature of the coolest point in the lamp i-~ in excess
of 500 C. The discharge tube is dosed with the following constituents~
which may be introduced by using an appropriate selection from rare gaqes
(Ne~ Ar~ Kr~ Xe)~ tin halides~ mercury halides~ sodium halides~ tin metal~
~5 sodium metal, mercury, complex halides of tin and sodium, elementalhalogens or other convenient qource of the elementq concerned:-
: - : :: . . .: : : ~ : , - , :: , , ,
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071:)368
1. ~ totnl pressure of 5 to 100 torr ~at 20 & ) of rare gas or
a mixture of rare aa~e~.
2. Tin ~n the r3n~e 5 - lOO ~mol zm 3.
3. One or more of the ~odium halides NaCl~ NaDr~ NaI~ to give
a total quantity of sodium halide in the range 1 - 250 ~m~l cm 3.
~. Additional halogen atoms which should include Cl or ~r in the
- range 5 - 100 ~mol cm 3~ with
(a) an atomic ratio of Cl/~ in the range 0.5 to 5j or;
(b~ an atomic ratio of Br/$ in the range 0.5 to 5~ or -
~c) bromine only present. ~ -
5. Mercury in the range 10 to 150 pmol cm 3.
In the accompanying drawing~
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~ Fi~. 1 is a side view of one example of a discharge tube
suitable for the purposes o~ this invention; and
Fi~. 2 i~ a side ~ie~ of a iurther example of a form of di~c-arge
la~p al~o suitable for this in~ention.
In the lamp Or Fig. 1 a silica discharge tube 11 iR closed at ;~
either end by pinches 12 which make hermetic seals round the current leads
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13. These current leads are oonnected to tungsten electrodes 14 which may
incorporate electron emissive material. The discharge operates betw-en
the electrodes. The discharge tube has an internal diameter of 6 mm with
the tips of the tun~sten electrodes separated by 20 mm. The volume may
typically ba 1 cm'. A ~imilar dischar~e tuba~ shown in Fig. 2~ has a
volume of 4.3 cm3~ an internal diameter of 15 in the centre and electrode -
separation 20 mm. An auxili~ry electrode 16 mny be included to assi~t in
~tartin~. The ends nre shaped to make the temperature of the coole~t
region a~ hi~h a~ possible. In both examples~ the temperature of the
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~o70368:
end~ of the di~chnr~e tube may al~o be increaed by n eoatin~ Or
zireonia on the tube end-~ or by any other ~uitable meana.
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In both example~ the di~char~e tube ean be mounted in a
eon~entional type of hard ~la89 bulb ~a~ shown Sor ex~nple in Fl~. 2
5 preferably With a ~upport frame of a type known to inhibit sodium
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misration through the di~eharge tube.
' The following are ex~nples which illustrate tho practice~of~
the in~ention. ,-
~xampie 1 ' , ~ ~'
io A diseharge tube of the type ~hGwn in ~i~. 1 wa~ dosed with ~'
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the followin~ components, expressed as wei~ht per em3 s~
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' H92C12 ' 6.2 mg - , ~ ,
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' 8~I2 3.1 m~
' Hg, 18.2 m~
1g' ' ' Sn , ' 4.9 my , '' '
NaCl 0.88 mg and also with s
- - Ar~o~ - - 5D torr at room ~emperature. ,
_, ,
- '- This di~eharge tube therefore contained 41 ~mol em 3'Sn~
15.1 ymol cm 5 NaCl~ other halogen atoms (Cl~I) 39.9 ~mol cm 3~ iD an
~0 atomie ratio Cl:I of 2:1~ and mereury 12~ /umol em 3. ,~ , ',
' Thi~ dischar~e lamp eould be operated with the following'',,
eharacteristieq: power 260W~ effieaey 90 ImW , temperature of eonden~ed '~
halide 700C~ ehromaticity eoordinate'~ ~ ~ .385~ y = .387~ eorr~lated ~
eolour temperature 3~50 ~ CI~ ~eneral eolour renderin~ indes 76.~ ,
~5 ~ 3 . ~ ~
A disch~r~e tube of the type shown in Flg. 1 waY do~ed with '
the ~me component~ a~ ~n Example 1 except that the ~odium chloride ,,
W~i~ht wa3 2.9 m~ em 3 ~50 ~moI cn 3),
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107(~368
This discharge lamp could be operated with the foIlowing ','
characteristicss power 260W, efficacy 95 lmW ~ temperature of
condensed halide 700 C, chromaticity coordinates x = .385, y = .38l,,
correlated colour temperature 3900X~ CI~ general colour rendering ~ '
index 72. -,
These two examples illustrate that the chromaticity co~
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, - ordinates are very insensitive to the proportion of NaCl.
~xample 3
,, A discharge tube of the type shown in Fig. 2 was dosed with the following~ ,
10 ~ components~ expressed a~ weight per cm3: , ' ~ , ~' "' '~ "'^-
- HgzCl2 o.76 mg - ~ ~ -
~GI2 0.72 mg ,, ,, ~ "
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Hg 3.03 mg
,
Sn 0.59 mg
NaCl 0.30 mg and also with~
Argon 30 torr at room temperature.
Th;s discharge tube therefore contained 5.0 ~mol cm 3 Sn, 5.1 ymol cm 3 '
NaCl~ 6.4 ~mol cm 3 other halogen atoms (Cl~ I) in an'atomic ratio ClsI of
and mercury 19.9 ymol cm 3. ~ '
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Thls discharge lamp could be operated with the following characteri~tic~:
power 253W~ efficacy 50 lmW ~ temperature of condensed,halide 590 & ~
chromaticity coordinates x = .359~ y = .375~ correlated colour temperature' ' -
4600 K~ CIE general cDlour renderin~ index 56. It could also be operated
at 400W when the efficacy was 69 lmW , the chromaticity coordinate~; ' -
25 x = .359~ y = .354~ correlated colour temperature 4500 K and CI~ general '
colour rendering index 65. '!'
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