Electric lamp and discharge devices – With gas or vapor – With particular gas or vapor
Reexamination Certificate
1999-12-06
2002-11-19
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
With particular gas or vapor
C313S643000
Reexamination Certificate
active
06483241
ABSTRACT:
TECHNICAL FIELD
The invention proceeds from a metal halide lamp according to the preamble of claim 1. It deals with mercury-free metal halide lamps, preferably with a ceramic discharge vessel.
PRIOR ART
The use of the halides of hafnium and/or zirconium for metal halide lamps together with mercury as the buffer gas has long been known. EP-B 627 759 has disclosed a metal halide lamp with a high light efficiency which uses mercury as the buffer gas. One exemplary embodiment in that document also shows a mercury-free fill for daylight use, with a color temperature of 5350 K, using HfBr
4
as the metal halide and with an addition of elemental tin. In this case, xenon (cold filling pressure 1 bar) takes over the role of the buffer gas. However, these lamps have enormously high restarting peaks of about 600 V and therefore can only be operated with complex circuit engineering. In addition, the service lives of the lamps described in this document lie between a few hours and, at best, 2100 hours. These lamps are therefore unsuitable for general-purpose illumination.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a metal halide lamp according to the preamble of claim
1
which does not contain any mercury and is still able to achieve a long service life of greater than 5000 hours.
This object is achieved by means of the characterizing features of claim
1
. Particularly advantageous configurations are given in the dependent claims.
The invention firstly provides Hg-free metal halide lamps, in particular with a ceramic discharge vessel, with properties similar to those which are already known for metal halide lamps with a discharge vessel made from quartz glass and Hg-containing fill, i.e. a high light efficiency of at least 70 Im/W and a high color rendering index Ra of at least 80, preferably for low outputs of up to 250 W. In this case, the service life is at least 5000 hours. The light color lies in the range from warm white to daylight white. Operation is advantageously on an electronic ballast.
For the first time, it has now become possible to achieve excellent maintenance of the light flux. Blackening of the wall of the discharge vessel is substantially avoided. This results from an optimization of the tungsten cycle which is no longer, as is generally known, controlled only by means of the halogens in the fill, which are usually present in the form of metal halides. Surprisingly, it has emerged that the addition of the metals Hf and/or Zr (“HZM”) as halides (“HZH”), while maintaining certain concentration relationships, improves the efficiency of the cycle decisively and thus allows long service lives even with Hg-free fills.
The discharge vessel may be a quartz glass bulb. Preference is given to a ceramic discharge vessel which may be tubular or bulged.
One condition for a cycle which proceeds particularly efficiently is a specific minimum concentration of metals which are active in the cycle (“HZM”), primarily Hf and Zr. They are present in the form of their halides, abbreviated as halides of hafnium and/or zirconium (“HZH”). Suitable halogens X are bromine, chlorine and iodine. The specific quantity of HZH in the discharge vessel must be at least 3 &mgr;mol/cm
3
:
HZH≧
3 &mgr;mol/cm
3
.
It is a fortunate state of affairs that these two metals at the same time have pronounced properties relating to the formation of a voltage gradient, so that they are able to partially replace the mercury in this respect. However, it is necessary for at least one further metal halide to be added to the fill as a voltage generator, in order to achieve as good a match as possible to the voltage gradient of mercury.
Metal halides MYn which vaporize readily and where Y is a halogen selected from bromine, chlorine and iodine are suitable for this purpose. These readily vaporizable metal halides are generally present in completely vaporized form, since they have a boiling point or a sublimation point of at most 1100 C. This temperature is reached at the vessel wall primarily when operating ceramic discharge vessels. Furthermore, elemental metals are suitable additions in order to make the cycle particularly effective and, in this way, to ensure a long service life of more than 6000 hours. Suitable elemental metals N are those which, together with free halogens, are able to form metal halides or metal halide complexes which vaporize readily at typical wall temperatures of around 1000° to 1100° C. The following metals are suitable in elemental form or as metal halides: Al, Bi, In, Mg, Sc, Sn, Tl, Zn, Sb, Ga.
The sum of the amount of halogen X which is bonded in the Hf/Zr halides and the amount of halogen Y which is bonded in the added readily vaporizable metal halides MY
n
(in each case in &mgr;mol), based on the metal content (HZM) which is bonded in the Hf/Zr content, must maintain a specific range in order to ensure an efficient cycle:
5≧(
X+Y
)/
HZM≧
15.
A value of between 8 and 13 is preferred. Without the addition of further metal halides to the metals HZM (i.e. when using elemental metals as in the prior art), this ratio would be equal to 4.
In particular, it is possible to achieve a longer service life if the total molar metal content “G” of all the voltage gradient generators (inc. Hf and Zr, i.e. HZM) in the fill in relation to only the molar content of the metals Hf and Zr (“HZM”) is carefully measured. The metals G (i.e. the sum of M, N and HZM) are present in the fill as virtually completely vaporized metal halides and elemental metals or metals which, with free halogens, are able to form metal halides and metal halide complexes which are virtually completely vaporized at vessel-wall temperatures of typically 1050° C. The G/HZM ratio should be at most 12, i.e.:
G/HZM≧
12.
The natural lower limit, in accordance with the definition, is G/HZM=1.
This upper limit in the ratio between all the metals G which are added as voltage gradient generators and the metals Hf and Zr (HZM) which also affect the cycle results from the fact that if this upper limit in relation to the metals HZM which are active in the cycle is exceeded, there is an excessive concentration of competing metals (M and N) in the vicinity of the electrodes. This impairs the tungsten transport process and ultimately leads to significant worsening in the maintenance.
A further metal which promotes the cycle is titanium. It is therefore suitable as an addition to Hf or Zr, but should only constitute up to 50 mol % of the total amount of HZM.
In a particularly preferred embodiment, there is an excess of the total molar halogen content X+Y (normally bonded in the readily vaporizable halide compounds). The sum of X+Y is at least 1.4 times the total molar metal content G which is bonded in the readily vaporizable compounds MY
n
and metals N together, i.e.:
(
X+Y
)/
G≧
1.4.
Setting this ratio is assisted in particular by the high valency of the HZH (their valency is normally four).
If all the conditions mentioned above are satisfied, the result is an optimum cycle which leads to service lives of over 6000 hours.
The most suitable operating mode is a square-wave current injection with a high edge gradient (i.e. a duration of the voltage change during a polarity change between two square-wave pulses of different polarity), preferably less than 30 &mgr;s. Operation with constant output is advantageous.
In the case of Hg-free metal halide lamps, metal halides with a high vapor pressure which, at the wall temperatures which are established in the discharge vessel, pass either completely or predominantly into the vapor phase are used to set the voltage gradient in the discharge arc and to set the thermal properties of the lamps. Typical examples of voltage gradient generators in long-life systems which are suitable as an addition to Hf and Zr are halides of In, Zn, Al, Mg. Further suitable additions are the metal halides of Bi, Sc, Sn, Tl, Sb and Ga. These are combined as G (total metals in the voltage gradient generators).
However, the voltage gradient generators,
Clove Thelma Sheree
McNeill William H.
Patent-Treuhand-Gesellschaft fuer elektrische Gluehlampen mbH
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