Patent Publication Number: US-7595593-B2

Title: Metal halide lamp with an ionizable fill with vanadium and rare earths, excluding manganese

Description:
TECHNICAL FIELD 
   The invention is based on a metal halide lamp or a high-pressure discharge lamp having an ionizable fill comprising at least one inert gas, mercury, with at least one halogen, the fill comprising Tl, Cs and rare earths as metals. It deals in particular with fills for lamps with a luminous color similar to daylight. 
   BACKGROUND ART 
   To achieve luminous colors similar to daylight, metal halide discharge lamps generally contain thallium. By way of example, U.S. Pat. No. 6,107,742 describes a lamp which contains a metal halide fill comprising the metals Cs, Tl, and rare earths, such as Dy, Tm, Ho, and has a luminous color similar to daylight. 
   Moreover, US-A 2003184231 has disclosed a fill for metal halide lamps which contains V and Mn halide. The fill may additionally contain metal halides comprising the metals Cs, Tl, and rare earths, such as Dy, Tm, Ho. Mn is used as a replacement for Na. The purpose of this is to lower the color temperature. 
   Finally, DE-A 35 12 757 has disclosed a fill for metal halide lamps which contains a metal silicide, such as V 5 Si 3 . The fill additionally contains rare earth or Sc halide and the corresponding rare earth oxyhalide and/or Sc oxide. The silicide in this case acts as a halogen getter. 
   US-A 2004253897 has disclosed a metal halide lamp with a two-ended outer bulb which surrounds only part of the discharge vessel. 
   DISCLOSURE OF THE INVENTION 
   It is an object of the present invention to provide a metal halide fill for metal halide discharge lamps having an ionizable fill comprising at least one inert gas, mercury, with at least one halogen, the fill comprising Tl, Cs and rare earths as metals, which are adapted to particular conditions of an outer bulb. 
   This object is achieved by the following features: the fill additionally comprises V halide. 
   Particularly advantageous configurations are given in the dependent claims. 
   The invention uses a metal halide fill which uses Cs, Tl and rare earths and, in addition, V halide. Other components with further halides are not used. The halogen used is iodine and/or bromine. Mn is not used, since there is no need to lower the color temperature and, on the contrary, the aim tends to be a high color temperature of at least 5000 K. Given this objective, the color temperature is set primarily by the rare earths. 
   When producing metal halide lamps with discharge vessels made from quartz glass, it has been found that considerable cost savings can be achieved by using a new design with an outer bulb, in which the outer bulb only partially surrounds the discharge vessel. A gas fill is used in the outer bulb. However, this leads to an altered temperature balance for the discharge vessel. The fill comprising metal halides of Cs, Tl and rare earths that has hitherto been customary has too much of a green tinge under these conditions. 
   The accurately metered addition of vanadium halide remedies this problem. In this case, a fill which contains between 0.1 and 2.5 mg of rare earth halides per ml of volume of the discharge vessel is used. A value from 0.2 to 2.0 mg/ml is preferred. Suitable rare earths are in particular Dy, Ho and Tm alone or in combination. Dy alone is particularly preferred. 
   The molar ratio between rare earths and vanadium should be between 1.5 and 30, in particular between 2 and 20. Since both variables are trivalent, this range also applies to the associated metal halides. The fill preferably contains more iodine than bromine. In particular, iodine alone is used, with a bromine content of at most 10% in molar terms. 
   If the absolute fill quantity for rare earths is exceeded, the color temperature becomes too low. If the quantity of rare earths in the fill is below the absolute limit, the color temperature becomes too high. 
   If the molar ratio of RE to V is exceeded, the y component of the color locus becomes too high and the color locus has too much of a green tinge. If the molar ratio of RE to V is below the lower limit, the luminous flux becomes too low. 
   This fill is particularly suitable for relatively high-wattage lamps with a rated power of at least 100 W. It is suitable in particular also for lamps with a relatively high rated power of up to 400 W. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The text which follows is intended to provide a more detailed explanation of the invention on the basis of a number of exemplary embodiments. In the drawings: 
       FIG. 1  shows a metal halide lamp according to the invention; 
       FIG. 2  shows a spectrum of this lamp; 
       FIG. 3  shows the change in color temperature over the life of this lamp; 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
     FIG. 1  shows a side view of a metal halide lamp  1  which is pinched on two sides. The discharge vessel  2  made from quartz glass, which is designed in the shape of a barrel, encloses two electrodes  3  as well as a metal halide fill. The bulb ends are sealed by pinches  4 , in which foils  5  are embedded. A fused seal is also suitable for sealing purposes. These foils are connected to external supply conductors  6 . The external supply conductor  6  is guided within a tubular sleeve  7  and ends in a socket  8  of an integral cap part  9 . The cap is produced in a single piece from steel or other heat-resistant metal and also comprises a circular disk  10  as contact element and barb  11  as centering and holding means. The convex part of the discharge vessel is partly surrounded by an outer bulb  12 , which is rolled on ( 13 ) in the region of the transition between the pinch  4  and the sleeve  7 . 
   The outer bulb  12  has an encircling indentation  14 , so that an elastic support strip  15  made from metal is spread along the inner surface of the outer bulb. The support strip may if necessary contain getter materials, such as Zr, Fe, V, Co. These materials are used to absorb various substances, such as oxygen, hydrogen or the like. The outer bulb may be filled with nitrogen, another inert gas or also a vacuum. 
   In another exemplary embodiment, an outer bulb gas mixture of N 2  and/or CO 2  with Ne is used to improve the ignition properties, in which case the total pressure is between 200 and 900 mbar. In this case, the starting gas used in the burner is an Ne—Ar—, Ne—Kr— or Ne—Ar—Kr Penning mixture. In particular an outer bulb gas mixture of N 2 /Ne or CO 2 /Ne with a total pressure of from 300 mbar to 900 mbar is used to maintain the good ignition properties throughout the service life. The Ne in this case forms between 25 and 60%. 
     FIG. 2  shows the spectrum of a 150 W lamp after a burning time of 100 h in accordance with the exemplary embodiment shown in  FIG. 1 , the discharge vessel of which contains 15 mg of Hg and the metal halide fill shown in Table 1. The fill in the outer bulb is argon. 
   As rare earth, the lamp uses Dy alone. Good results are also achieved with an addition of Tm and Ho if Dy is used predominantly, representing a proportion of more than 50%. 
     FIG. 3  shows the change in the luminous flux LF ( FIG. 3   a , curve a) and the color temperature Tn ( FIG. 3   b , curve a) of the lamp from  FIG. 1  as a function of the service life. Both characteristic variables are extremely stable until a service life of at least 6000 hours. 
   Table 1 shows a further exemplary embodiment relating to a 250 W lamp and a 400 W lamp with daylight fill. In both cases, the fill is of similar composition to the 150 W exemplary embodiment. The corresponding profiles of the luminous flux and the color temperature are plotted in  FIGS. 3   a  and  3   b  as curves b) for the 250 W exemplary embodiment and c) for the 400 W exemplary embodiment. 
   
     
       
         
             
             
           
             
                 
               TABLE 1 
             
           
          
             
                 
                 
             
             
                 
               Power/W 
             
          
         
         
             
             
             
             
          
             
                 
               150 
               250 
               400 
             
             
                 
                 
             
          
         
         
             
             
             
             
          
             
               Luminous 
               11 000   
               18 500   
               35 000   
             
             
               flux/lm 
             
             
               Color 
               5500 
               5500 
               5600 
             
             
               temperature/K 
             
             
               Mean service 
               9000 
               9000 
               9000 
             
             
               life/h 
             
             
               Electrode 
                15 
                 27.5 
                 30.5 
             
             
               gap/mm 
             
             
               Burner bulb 
                 14.8 
                18 
                24 
             
             
               diameter/mm 
             
             
               Burner bulb 
                 22.3 
                32 
                46 
             
             
               length/mm 
             
             
               Bulb 
                 1.6 
                 5.2 
                 14.5 
             
             
               volume/ml 
             
          
         
         
             
             
             
             
             
             
             
          
             
               Burner fill 
               100 
               hPa Ar 
               100 
               hPa Ar 
               100 
               hPa Ar 
             
             
               gas 
             
          
         
         
             
             
             
             
             
          
             
               Outer bulb 
               300 
               hPa Ar 
               Vacuum 
               Vacuum 
             
             
               fill gas 
             
          
         
         
             
             
             
             
             
             
             
          
             
               Fill in mg 
               15 
               mg Hg, 
               14 
               mg Hg, 
               60 
               mg Hg, 
             
             
                 
               0.41 
               mg CsJ, 
               0.90 
               mg CsJ, 
               1.8 
               mg CsJ, 
             
             
                 
               1.53 
               mg DyJ3, 
               3.35 
               mg DyJ3, 
               6.7 
               mg DyJ3, 
             
             
                 
               0.47 
               mg TlJ, 
               1.0 
               mg TlJ, 
               2.0 
               mg TlJ, 
             
             
                 
               0.1 
               mg VJ3 
               0.2 
               mg VJ3 
               0.4 
               mg VJ3 
             
             
               Metals in 
               Cs 
               26% 
               Cs 
               26% 
               Cs 
               26% 
             
             
               mol % 
               Dy 
               46% 
               Dy 
               46% 
               Dy 
               46% 
             
             
                 
               Tl 
               23% 
               Tl 
               23% 
               Tl 
               23% 
             
             
                 
               V 
               5% 
               V 
               5% 
               V 
               5%