Abstract:
An amalgam capsule ( 16 ) for a low-pressure mercury vapor discharge lamp ( 1 ) has a closed end and an opposing end with an opening ( 21 ) to allow passage of mercury vapor between the amalgam plug ( 18 ) and the discharge space ( 3 ) of the lamp ( 1 ). A glass rod ( 19 ) placed in the capsule ( 16 ) restrains movement of the amalgam plug ( 18 ), and projections ( 20 ) in the inner wall of the capsule ( 16 ) restrain movement of the glass rod ( 19 ). The presence of the amalgam capsule ( 16 ) in the discharge space ( 3 ) enables highly-loaded, substantially temperature-independent operation of linear fluorescent lamps such as T8 lamps.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to low-pressure mercury vapor discharge lamps, and more particularly relates to such lamps which utilize amalgam to achieve a measure of temperature-independent operation. 
         [0002]    Low-pressure mercury vapor discharge lamps, commonly referred to as fluorescent lamps, generally take the form of a sealed glass tube containing electrodes, mercury (Hg) and an inert gas, and internally coated with a phosphor layer. 
         [0003]    The electrodes provide an electrical interface between external power and an internal plasma that forms between the electrodes during lamp operation. The mercury vapor absorbs electrical energy and emits UV radiation, while the phosphor layer absorbs UV radiation emitted by the mercury and emits longer wavelength UV radiation and/or visible light, depending on the particular type of lamp and its intended application. 
         [0004]    The mercury vapor pressure is key to the efficient operation of such a fluorescent lamp. If too little mercury vapor exists in the plasma discharge, little UV radiation will be produced, and if too much mercury vapor exists in the plasma discharge, some of the UV radiation will get reabsorbed by the excess mercury vapor, reducing light output and causing inefficient power usage. 
         [0005]    A common technique for control of the mercury vapor pressure in the discharge space is to design the lamp with a cold spot to which excess mercury vapor can condense, so that an equilibrium is established between the condensed mercury and the mercury vapor. Unfortunately, this technique is only useful over a relatively narrow temperature range. When the temperature in the discharge vessel increases much above this temperature range, for example, because the ambient temperature increases, the output efficiency decreases. 
         [0006]    Another well-known method for control of the mercury vapor pressure involves the use of a mercury amalgam. This method allows the lamp to operate efficiently at a wider range of temperatures than standard fluorescent lamps employing cold spot technology. This method is commonly used in compact fluorescent lamps, but rarely used in linear or U-bent fluorescent lamps. 
         [0007]    Using amalgams in fluorescent lamps requires methods which ensure against loss of mercury to the environment during handling and storage; which ensure that the amalgam stays in the proper location during lamp processing and operation; and which is compatible with high speed fluorescent lamp equipment and processes while also being cost effective. If sealed amalgam capsules are used, then the method must include the step of opening the capsule in the finished sealed lamp. See in this regard U.S. Pat. No. 4,288,715 and EP 0 063 393. 
         [0008]    International Patent Application Publication WO 2006/000974 A2, the entire specification of which is incorporated by reference herein, discloses a low-pressure mercury vapor discharge lamp employing an amalgam to control mercury vapor pressure. The lamp is said to offer a compact design by locating the amalgam in a glass capsule ( 12 ) mounted inside the tubular glass vessel ( 2 ) which encloses the discharge space ( 3 ). The capsule ( 12 ) encloses an amount of amalgam ( 13 ) and has a gas opening at one end to enable gas exchange between the amalgam ( 13 ) and the discharge space ( 3 ). A glass rod ( 15 ) is located between the amalgam ( 13 ) and the gas opening ( 14 ) to prevent the plug of amalgam ( 13 ) from escaping from the capsule ( 12 ). 
         [0009]    A drawback of the above arrangement is that the rod is not secured in the capsule and thus can move during lamp processing and/or operation, enabling the amalgam to move relative to its optimal location in the lamp, and even allowing portions of the amalgam to escape from the capsule. 
         [0010]    According to the invention, a low-pressure mercury vapor discharge lamp comprises a glass vessel enclosing a discharge space containing mercury and an inert gas, the glass vessel being provided with at least one glass stem located within an end portion of the glass vessel, and also comprises a container encapsulating at least one plug of amalgam, the container being provided with an opening enabling gas exchange between the amalgam and the discharge space, the container also being provided with at least one spacer located between the amalgam and the opening to restrain movement of the amalgam within the container, the lamp being characterized in that the container also includes means for restraining the movement of the spacer within the container. 
         [0011]    For the sake of convenience, the term ‘amalgam’ as used herein means both an amalgam of mercury with one or more other metals or alloys, as well as the pre-amalgam metal(s) or alloy(s) which may initially reside in the container or capsule, and which become amalgamated with mercury during subsequent lamp start-up and/or operation. Starting with a pre-amalgam metal or alloy in the capsule eliminates the potential loss of mercury during storage, handling and lamp manufacture. Mercury is then introduced into the lamp separately, in any of several known ways. 
         [0012]    Suitable amalgam-forming metals and alloys are well-known, and include for example, indium, bismuth-indium alloys, and silver, lead, tin and their alloys. 
         [0013]    The capsule is mounted inside the discharge space of the lamp, for instance, to an electrode shield or a metal collar easily attached (e.g., by welding) to an inner lead wire or an existing auxiliary wire of the lamp. The capsule, via its location and distance from the electrode, sets the operating temperature of the amalgam and constrains its movement at lamp operating temperatures. 
         [0014]    Suitable means for restraining the spacer(s) in the capsule include metal wires and projections or annular ridges on the inner wall of the capsule. Suitable spacers include rod(s) and/or tube(s) of a heat-resistant glass, such as quartz or borosilicate glass. 
         [0015]    According to a preferred embodiment of the invention, the capsule contains a main amalgam plug near the closed end of the capsule, an auxiliary amalgam plug near the opening in the capsule, a first spacer located between the main amalgam plug and the auxiliary amalgam plug, and a second spacer located between the auxiliary amalgam plug and the opening in the capsule. 
         [0016]    According to another preferred embodiment of the invention, the amalgam capsule contains a magnetic plug in addition to the amalgam plug, and the amalgam capsule is moveably mounted inside a larger capsule having a fixed position within the discharge space, so that the amalgam capsule can be moved by means of an external magnet after lamp sealing has taken place, enabling adjustments to the location of the amalgam capsule to compensate for varying internal and/or external conditions. 
         [0017]    The invention is usefully embodied, for example, in highly loaded substantially temperature-independent linear fluorescent lamps such as those having tubular envelopes of the type “T8”, efficiently operable over a temperature range of about 20 to 150 degrees F. at a power rating of about 80 to 85 W, compared to a temperature range of about 32 to 77 degrees F. and a power rating of about 25-40W for standard T8 lamps without amalgam. 
         [0018]    The invention is compatible with modern high speed horizontal lamp-making equipment, and can be readily integrated into existing manufacturing technologies for linear fluorescent lamps such as the T8 lamp. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    These and other aspects of the invention will be further elucidated with reference to the Figures, in which: 
           [0020]      FIG. 1  shows a low-pressure mercury vapor discharge lamp having an amalgam capsule with retaining means according to one embodiment of the invention; 
           [0021]      FIG. 2  shows an amalgam capsule with retaining means according to a second embodiment of the invention; 
           [0022]      FIG. 3  shows an amalgam capsule with retaining means according to a third embodiment of the invention; 
           [0023]      FIG. 4  shows an amalgam capsule with retaining means according to a fourth embodiment of the invention; 
           [0024]      FIG. 5  shows an amalgam capsule with main and auxiliary amalgams according to a fifth embodiment of the invention; 
           [0025]      FIG. 6  shows a moveable amalgam capsule according to a sixth embodiment of the invention; and 
           [0026]      FIG. 7  shows the location of the moveable amalgam capsule of  FIG. 6  in a fixed capsule according to the sixth embodiment of the invention. 
       
    
    
       [0027]    The Figures are diagrammatic and not drawn to scale. The same reference numbers in different Figures refer to like parts. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]      FIG. 1  shows a schematic view of a low-pressure mercury vapor discharge lamp  1  according to the invention, having a straight elongate tubular glass vessel  2  of the type generally know as a TL-lamp, which encloses a discharge space  3  which is filled with a gas mixture of an inert gas such as argon, and mercury (mercury) vapor. The glass vessel has two distal ends  4  and  5  provided with electrodes  6  and  7  mounted on conductors  8  and  9 , and  10  and  11 , respectively. The conductors ( 8 ,  9 ,  10 ,  11 ) pass through gas-tight press seals  12  and  13 , formed in the ends of the vessel  2  from tubular glass stems, after the discharge space  3  is filled with the gas mixture, in the known manner. The portions of the conductors which extend outside the discharge space form contact pins for the supply of electrical power to the electrodes  6  and  7 . The electrodes  6  and  7  are surrounded by metal shields  14  and  15 , which have the function of reducing end darkening during lamp operation and also serve as a convenient mounting location for capsules. 
         [0029]    A glass capsule  16  is mounted on shield  15  by a mounting member  17 . The glass capsule  16  has a closed end and an open end with an opening  21 . A quantity of amalgam  18 , for instance a bismuth-indium amalgam. is situated near the closed end of the capsule  16  and a glass rod  19  is located between the amalgam  18  and the open end of the capsule  16  to restrain movement of the amalgam  18 . The glass rod has a diameter smaller than the inside diameter of the capsule, enabling mercury vapor to pass between the amalgam  18  and the discharge space  3  via the opening  21 . 
         [0030]    In accordance with the invention, restraining means in the form of protrusions  20  from the inner wall of the glass capsule  16  are provided to restrain movement of the glass rod  19  in the capsule  16 . Protrusions  20  may take the form of one or more raised portions or a continuous annular ridge or any other form which will serve to restrain movement of the glass rod  19 . 
         [0031]    The location of the capsule is determined by the desired distance between the electrode  7  and the amalgam  18  to result in optimal performance of the lamp. 
         [0032]      FIG. 2  shows a second embodiment of the amalgam capsule for use in the fluorescent lamp of the invention. Capsule  22  has an open end  23 , an amalgam plug  24  located near the opposite, closed end of the capsule  22 , a glass rod  25  and short length of wire  26  for restraining movement of the glass rod  25 . 
         [0033]    Exemplary of this embodiment is a capsule  22  made of borosilicate capillary glass tube having an ID of 2 mm and an OD of 2.4 mm, a quartz rod  25  having a diameter of 1.5 mm, and a 0.014-0.015 gauge stainless steel wire, 4-8 mm in length. One end of the capillary glass tube is sealed by heating, after which the wire  26  is inserted. Small balls (or short pieces of wire) of indium metal or bismuth-indium alloy 1.4-1.5 mm in diameter are next added to the tube near its sealed end. The sealed end is then heated with a hot air gun to melt the balls or wire pieces into a plug  24  surrounding the stainless steel wire. Next the quartz rod  25  is added to the capsule to form a chamber containing the wire and the amalgam plug. The open end of the tube is then fire polished to glaze the glass and reduce the tubing diameter to a small opening, e.g., less than 1.5 mm diam., which is sufficient to allow ready passage of mercury vapor, without allowing the quartz rod to move out of the tube. 
         [0034]      FIG. 3  shows a third embodiment of a capsule suitable for use in a lamp of the invention. Capsule  32  has an open end  33 , an amalgam plug  34  located near the opposite, closed end of the capsule  32 , and a glass rod  35  for restraining movement of the plug  34 . In this embodiment, the wire  26  is replaced by projections  36  and  37  as the means for restraining movement of the glass rod  35 . 
         [0000]    An exemplary procedure for forming capsule  32  is similar to that described for capsule  22 , except that after forming the closed end of the tube, the balls of amalgam are then added and heated to form the plug. The projections are formed by using a small burner to create indentations in the outer wall of the capsule, forming a chamber for the amalgam plug at the sealed end of the capsule. 
         [0035]      FIG. 4  shows a fourth embodiment of a capsule suitable for use in a lamp of the invention. Capsule  42  has an open end  43 , an amalgam plug  44  located near the opposite, closed end of the capsule  42 , and a glass tube  45 , closed at one end, for restraining movement of the plug  44 . In this embodiment, the glass tube  45  is restrained by a projection  46 , which is formed by as described above. 
         [0036]      FIG. 5  shows a fifth embodiment of a capsule suitable for use in a lamp of the invention. Capsule  52  has an open end  53 , a first amalgam plug  54  located near the opposite, closed end of the capsule  52 , and a second amalgam plug  56  near the open end  53  of the tube  52 . A first glass rod is located between the plugs  54  and  56 , while a second glass rod  56  is located between the second plug  56  and the open end  53  of the tube  52 . Glass rods  55  and  57  separate the plugs  54  and  56  from one another, and also restrain movement of the plugs  54  and  56  in the capsule  52 . In this embodiment, the glass rods  55  and  57  are restrained by projections  58 ,  59  and  60 , which are formed in the same manner as the projections  36  and  37  of the third embodiment described above. 
         [0037]    By means of the second plug  56 , a secondary amalgam (auxiliary amalgam) is available to operate during lamp warm-up. The secondary amalgam quickly releases mercury to improve lamp run-up characteristics when initially lit. 
         [0038]    The length and location of the capsule  52  in the lamp determine the locations and temperatures of the main and auxiliary amalgams during lamp operation. 
         [0039]      FIGS. 6 and 7  show a sixth embodiment of a capsule suitable for use in a lamp of the invention.  FIG. 6  shows a moveable capsule  62  having an open end  63 , an amalgam plug  64  located near the opposite, closed end of the capsule  62 , a magnetic plug  66  located near the open end  63 , and first and second glass rods  65  and  67  separating the plugs  64  and  66  from one another and from the open end  63 . Movement of the plugs  64  and  66  and the glass rods  65  and  67  is restrained by projections  68 ,  69  and  70 . 
         [0040]      FIG. 7  shows a second capsule  72  with open ends  73  and  74  for passage of mercury vapor. Capsule  72  is located in a fixed position within the discharge space  3  of the lamp, while the moveable capsule  62  is located within the fixed capsule  72 , to allow the relocation of the amalgam plug in a finished fluorescent lamp. 
         [0041]    The ability to relocate the position of the amalgam plug in a finished lamp enables adjustments to the distance of the plug from the proximal electrode (which changes the temperature of the plug) to optimize the mercury pressure according to varying ambient and lamp loading conditions, as well as to decreasing amounts of mercury as it is consumed over the life of the lamp, thus optimizing and/or maintaining the efficiency of lamp operation. 
         [0042]    The amalgam plug can also be moved closer to the electrode during lamp start-up to more quickly reach a steady state, and then moved away from the electrode to an optimal location for steady-state lamp operation. 
         [0043]    The outer glass tube  72  is mounted in the discharge space  3 , for instance, by means of a non-magnetic collar attached to an inner lead wire (or auxiliary wire if available) to rigidly fix its location in the end of the lamp. The outer tube  72  is oriented so that movement of the capsule  62  along the tube moves the amalgam plug  65  closer to or further away from the proximal electrode  7 . Movement of the capsule  62  is accomplished by moving an external magnet adjacent to the location of the magnetic plug  66 . Based on the exemplary dimensions set forth above for the second embodiment of the capsule, the metallic plug  66  is an iron plug 1.4 mm in diameter. The ID of glass tube  72  is slightly larger than the OD of the capsule, for instance, 2.5 to 3.5 mm. 
         [0044]    The invention has necessarily been described in terms of a limited number of embodiments. From this description, other embodiments and variations of embodiments will become apparent to those skilled in the art, and are intended to be fully encompassed within the scope of the invention and the appended claims. For example, other embodiments might use other glasses or non-magnetic metal tubing for the spacers, and chamber forming inserts as the restraining means for the spacers.