CA1070368A - Electrical discharge lamp - Google Patents

Abstract

TITLE: ELECTRICAL DISCHARGE LAMP

ABSTRACT OF THE DISCLOSURE

Electrical discharge lamps containing mixed halides of superior performance are provided by the inclusion in the lamp of a volatile complex halide compound of tin and sodium. The halide may be added as a mixture of tin and sodium halide but the complex is formed in operation of the lamp and has a much higher volatility than the constituent halides. The preferred lamps contain 5 to 100 micromoles tin and 1 to 250 micromoles sodium halide per cubic centimetre.

Description

` 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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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:-: - : :: . . .: : : ~ : , - , :: , , , : ~ . .: .- . " ~ . ~

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~
- . . ~ .
~ 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 - ~ .
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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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.
. . ' .
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 ~ .
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 ~' .
the followin~ components, expressed as wei~ht per em3 s~
. .
' 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~
. ., , : .
, - 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 ,, ,, ~ "
.
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. ~ ' :. :
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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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTYOR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 5-100µ
mol cm-3 and wherein the fill contains 1-250µ 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 50µ mol cm-3.

2. A lamp according to claim 1 wherein the fill contains halogen additional to that supplied by said sodium halide and selected from chlorine and iodine in an atomic ratio from 0.5 to 5:1, bromine and iodine in an atomic ratio from 0.5 to 5:1 and bromine alone, such additional halogen amounting in total to 5 to 100µ mol cm-3.

3. A lamp according to claim 2 wherein the pressure of rare gas is 5 to 100 torr at 20°C and the quantity of mercury is in the range 50 to 150µ mol cm-3.

4. A lamp according to claim 1 or 3 wherein the lamp envelope is of fused silica.

5. A lamp according to claim 1 or 3 wherein the lamp envelope is of polycrystalline or single crystal alumina.