Abstract:
The invention relates to a high-pressure discharge lamp of the ceramic metal halide type of the Philips MasterColor® series having power ranges of about 150W to about 1000W. Such lamps are provided with a discharge vessel which encloses a discharge space. The discharge vessel has a ceramic wall and is closed by a ceramic plug. An electrode which is located inside the discharge space is connected to an electric conductor by way of a leadthrough element. The leadthrough element projects through the ceramic plug with a close fit and is connected thereto in a gas-tight manner by way of a sealing ceramic. The leadthrough element has a first part which is formed by a cermet at the area of the gas-tight connection. In addition, the lamps display one or more and most preferably all of the following properties: a CCT (correlated color temperature) of about 3800 to about 4500K, a CRI (color rendering index) of about 70 to about 95, a MPCD (mean perceptible color difference) of about ±10, and a luminous efficacy up to about 85-95 lumens/watt, a lumen maintenance of &gt;80%, color temperature shift &lt;200K from 100 hours to 8000 hours, and lifetime of about 10,000 hours to about 25,000 hours. The invention also relates to design spaces for the design and construction of high power lamps and methods for construction of such lamps using the design spaces.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a high-pressure discharge lamp which is provided with a discharge vessel that encloses a discharge space and includes a ceramic wall, the discharge space accommodating an electrode which is connected to an electric current conductor by means of a leadthrough element. The invention also relates to a high intensity discharge (HID) lamp having a discharge vessel light source, a glass stem, a pair of leads embedded in the glass stem, a glass envelope surrounding the light source, and a wire frame member with a first end fixed with respect to the stem, an axial portion extending parallel to the axis of the lamp, and a second end resiliently fitted in the closed end of the glass envelope.  
         BACKGROUND OF THE INVENTION  
         [0002]    High intensity discharge (HID) lamps are commonly used in large area lighting applications, due to their high energy efficiency and superb long life. The existing HID product range consists of mercury vapor (MV), high pressure sodium (HPS), and quartz metal halide (MH) lamps. In recent years, ceramic metal halide lamps (for example, Philips MasterColor® series) have entered the market place. Compared to the conventional HID lamps, the ceramic metal halide lamps display excellent initial color consistency, superb stability over life (lumen maintenance &gt;80%, color temperature shift &lt;200K at 10,000 hrs), high luminous efficacy of &gt;90 lumens/watt and a lifetime of about 20,000 hours. These highly desirable characteristics are due to the high stability of the polycrystalline alumina (PCA) envelopes and a special mixture of salts, which emits a continuous-spectrum light radiation close to natural light.  
           [0003]    The salt mixture used in Philips MasterColor® series lamps is composed of NaI, CaI 2 , TlI, and rare-earth halides of DyI 3 , HoI 3  and TmI 3 . NaI, CaI 2  and TlI are mainly for emitting high intensity line radiation at various colors, but they also contribute to continuous radiation. The rare-earth halides are for continuous radiation throughout the visible range, resulting in a high color rendering index (CRI). By adjusting the composition of the salts, color temperatures of 3800-4500K, and a CRI of above 85 can be achieved. The existing power range of such lamps is from 20W to 150W. The relatively narrow power range makes these products only suitable for the applications requiring low power installations, such as most indoor low-ceiling retail spaces. For large area, higher power applications requiring a lamp power of 200W to 1000W, the primary available products are MV, HPS and MH lamps.  
           [0004]    One example of a lamp of the kind set forth is known from U.S. Pat. No. 5,424,609. The known lamp has a comparatively low power of 150 W at the most at an arc voltage of approximately 90 V. Because the electrode in such a lamp conducts comparatively small currents during operation of the lamp, the dimensions of the electrode may remain comparatively small so that a comparatively small internal diameter of the projecting plug suffices. In the case of a lamp having a rated power in excess of 150 W, or a substantially lower arc voltage, for example as in the case of large electrode currents, electrodes of larger dimensions are required. Consequently, the internal plug diameter will be larger accordingly. It has been found that in such lamps there is an increased risk of premature failure, for example due to breaking off of the electrode or cracking of the plug.  
           [0005]    There is a need in the art for HID lamps of the ceramic metal halide type with power ranges of about 150W to about 1000W.  
         SUMMARY OF THE INVENTION  
         [0006]    An object of the invention is to provide HID lamps of the ceramic metal halide type with power ranges of about 150W to about 1000W. The nominal lamp voltage, as specified by applicable ANSI standards for HPS and MH varies from 100V to 135 V for 150W to 400W lamps and then increases with the rated power to about 260V for 1000W lamps.  
           [0007]    Another object of the invention is to provide ceramic metal halide lamps of the Philips MasterColor® series that display excellent initial color consistency, superb stability over life (lumen maintenance &gt;80%, color temperature shift &lt;200K at 10,000 hrs), high luminous efficacy of &gt;90 lumens/watt, a lifetime of about 20,000 hours, and power ranges of about 150W to about 1000W.  
           [0008]    Another object is to provide a way to mitigate the drawbacks and risks of failure discussed above.  
           [0009]    These and other objects of the invention are accomplished, according to a first embodiment of the invention in which an entire product family of gas discharge lamps with rated power of 150W to 1000W are provided which may be coupled with ANSI standard series of ballasts designed for high pressure sodium or quartz metal halide lamps (pulse-start or switch-start). The lamps of the invention are an extension of Philips MasterColor® series lamps to a power range of 150W to 1000W, and they are suitable for same-power HPS or MH retrofit. Therefore, they may be used with most existing ballast and fixture systems.  
           [0010]    In its preferred embodiments, the invention provides ceramic metal halide lamps having a power range of about 150W to about 1000W, suitable for high pressure sodium and/or quartz metal halide retrofit.  
           [0011]    In another preferred embodiment, such high power lamps as described above will have one or more and most preferably all of the following properties: a CCT (correlated color temperature) of about 3800 to about 4500K, a CRI (color rendering index) of about 70 to about 95, a MPCD (mean perceptible color difference) of about ±10, and a luminous efficacy up to about 85-95 lumens/watt.  
           [0012]    In another preferred embodiment, ceramic metal halide lamps are provided which have been found, regardless of the rated power, to have a lumen maintenance of &gt;80%, color temperature shift &lt;200K from 100 to 8000 hours, and lifetime of about 10,000 to about 25,000 hours.  
           [0013]    Especially preferred are ceramic metal halide lamps that display excellent initial color consistency, superb stability over life (lumen maintenance &gt;80%, color temperature shift &lt;200K at 10,000 hrs), high luminous efficacy of &gt;90 lumens/watt, a lifetime of about 20,000 hours, and power ranges of about 150W to about 1000W.  
           [0014]    The invention also provides novel design spaces containing parameters for any lamp power between about 150W and 1000W in which appropriate parameters for the body design of a lamp operable at the desired power is obtained by selection from parameters in which (i) the arc tube length, diameter and wall thickness limits are correlated to and expressed as functions of lamp power, and/or color temperature, and/or lamp voltage, and (ii) the electrode feedthrough structure used to conduct electrical currents with minimized thermal stress on the arc tube are correlated to and expressed as a function of lamp current. The invention also provides methods for producing ceramic metal halide lamps having predetermined properties through use of the design spaces of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The above aspects and further aspects of the lamps in accordance with the invention will be described in detail hereinafter with reference to the drawing in which:  
         [0016]    [0016]FIG. 1 is a graph illustrating a range of upper and lower limits for the dimensions of the arc tube inner length in a preferred embodiment of the invention;  
         [0017]    [0017]FIG. 2 is a graph illustrating a range of upper and lower limits for the dimensions of the arc tube inner diameter in a preferred embodiment of the invention;  
         [0018]    [0018]FIG. 3 is a graph illustrating a design space of the limits of aspect ratio in a preferred embodiment of the invention;  
         [0019]    [0019]FIG. 4 is a graph illustrating a design space of wall loading versus power in a preferred embodiment of the invention;  
         [0020]    [0020]FIG. 5 is a graph illustrating a range of upper and lower limits for the dimensions of the arc tube wall thickness versus the lamp power in a preferred embodiment of the invention;  
         [0021]    [0021]FIG. 6 is a graph illustrating a range of upper and lower limits for electrode rod diameter versus power in a preferred embodiment of the invention;  
         [0022]    [0022]FIG. 7 is a graph illustrating a range of upper and lower limits for electrode rod lengths versus power in a preferred embodiment of the invention;  
         [0023]    [0023]FIG. 8 is a schematic of a lamp according to a preferred embodiment of the invention;  
         [0024]    [0024]FIG. 9 is a sectional view of a ceramic arc tube of FIG. 8 according to a preferred form of the invention;  
         [0025]    [0025]FIG. 10 is a sectional view of a three-part electrode feedthrough of FIG. 8 according to a preferred form of the invention; and  
         [0026]    [0026]FIG. 11 is a graph of lumen maintenance of 150W and 200W lamps according to a preferred form of the invention. 
     
    
       [0027]    The invention will be better understood with reference to the details of specific embodiments that follow:  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Referring to FIG. 8, a ceramic metal halide discharge lamp  1  comprises a glass outer envelope  10 , a glass stem  11  having a pair of conductive frame wires  12 ,  13  embedded therein, a metal base  14 , and a center contact  16  which is insulated from the base  14 . The stem leads  12 ,  13  are connected to the base  14  and center contact  16 , respectively, and not only support the arc tube  20  but supply current to the electrodes  30 ,  40  via frame wire member  17  and stem lead member  13 . A getter  18  is fixed to the frame wire member  17 . Niobium connectors  19  provide an electrical connection for the arc tube electrode feedthroughs  30  and  40 . Beyond this the frame member  17  is provided with an end portion  9  that contacts a dimple  8  formed in the upper axial end of the glass envelope  10 .  
         [0029]    [0029]FIG. 9 shows a preferred embodiment of the arc tube  20  having a four-part feedthrough in cross-section. The central barrel  22  is formed as a ceramic tube having disc-like end walls  24 ,  25  with central apertures which receive end plugs  26 ,  27 . The end plugs are also formed as ceramic tubes, and receive electrodes  30 ,  40  therethrough. The electrodes  30 ,  40  each have a lead-in  32 ,  42  of niobium which is sealed with a frit  33 ,  43  which hermetically seals the electrode assembly into the PCA arc tube, a central portion  34 ,  44  of molybdenum/aluminum cermet, a molybdenum rod portion 35, 45 and a tungsten rod  36 ,  46  having a winding  37 ,  47  of tungsten. The barrel  22  and end walls  24 ,  25  enclose a discharge space  21  containing an ionizable filling of an inert gas, a metal halide, preferably a mixture of metal halides, and mercury.  
         [0030]    [0030]FIG. 10 shows a second preferred embodiment of the arc tube  20  having a three-part feedthrough in cross-section. The electrodes  30 ,  40  (only  30  is illustrated) each have a lead-in  32 ,  42  of niobium which is sealed with a frit  33 ,  43 , a central portion  34 ,  44  of molybdenum or cermet, and a tungsten rod  36 ,  46  having a winding  37 ,  47  of tungsten.  
         [0031]    As used herein, “ceramic” means a refractory material such as a monocrystalline metal oxide (e.g. sapphire), polycrystalline metal oxide (e.g. polycrystalline densely sintered aluminum oxide and yttrium oxide), and polycrystalline non-oxide material (e.g. aluminum nitride). Such materials allow for wall temperatures of 1500-1600K and resist chemical attacks by halides and Na. For purposes of the present invention, polycrystalline aluminum oxide (PCA) has been found to be most suitable.  
         [0032]    [0032]FIG. 8 also shows a ceramic metal halide arc tube  20  having a conductive antenna coil  50  extending along the length of barrel  22 . As described further hereinbelow, the antenna coil  50  reduces the breakdown voltage at which the fill gas ionizes by a capacitive coupling between the coil and the adjacent lead-in in the plug. When an AC voltage is applied across the electrodes, the antenna stimulates UV emission in the PCA, which in turn causes primary electrons to be emitted by the electrode. The presence of these primary electrons hastens ignition of a discharge in the fill gas.  
         [0033]    Thus to summarize, there is provided high wattage discharge lamps which comprise a ceramic discharge vessel which encloses a discharge space and is provided with preferably a cylindrical-shaped ceramic, preferably a sintered translucent polycrystalline alumina arc tube with electrodes, preferably tungsten-molybdenum-cermet-niobium electrodes, attached on either side by gas-tight seals. Metallic mercury, a noble gas or a mixture of noble gases and radioactive  85 Kr, and a salt mixture composed of sodium iodide, calcium iodide, thallium iodide and several rare earth iodides are contained in the arc tube. The arc tube is protected from explosion by a tungsten or molybdenum coil, which also serves as antenna for starting. The entire arc tube and its supporting structure are enclosed in a standard-size lead-free hard glass bulb, with other components such as a getter ( 18  in FIG. 8) or an UV enhancer (not shown) attached as necessary.  
         [0034]    In preferred embodiments of the invention, the following design parameters have been found to mitigate and in most cases eliminate the effects of higher thermal stress associated with the higher lamp powers. We have found the parameters to be especially suitable for the production of lamp products of 150W to 400W of power and 100V of lamp voltage, and with modifications in some of the design parameters, lamps with 135V-260V voltage and/or higher powers (up to 1000W) may also be designed. These design parameters are:  
         [0035]    (i) the general aspect ratio, i.e. the ratio of the inner length (IL) to the inner diameter (ID) of the PCA arc tube body is higher than that of low power-range MasterColor® lamps.  
         [0036]    (ii) general design spaces for any lamp power between 150W and 1000W, in terms of arc tube length, diameter and wall thickness limits, are expressed as functions of lamp power, color temperature, and lamp voltage and the upper and lower limits of such parameters are determined for the selected lamp powers and a method is provided for selecting parameters from the design space to provide a lamp with previously selected characteristics.  
         [0037]    (iii) a unique laser-welded Tungsten-cermet-Niobium or Tungsten-molybdenum-cermet-Niobium electrode feedthrough structure is used to conduct large electrical currents with minimized thermal stress on the PCA.  
         [0038]    (iv) the design parameter limits of such feedthroughs are given as the function of lamp current.  
         [0039]    (v) for reducing the risk of non-passive failure, a molybdenum coil wrapped around the arc tube and around the extended plugs is used as disclosed in our U.S. patent application Ser. No. ______ (Disclosure No. 701713 filed of even date herewith as a divisional application of this application for “Coil Antenna/Protection For Ceramic Metal Halide Lamps”.  
         [0040]    (vi) the salt composition is adjusted, to the desired color temperatures, for the geometry and varying lamp voltages of the high power MasterColor® lamps.  
         [0041]    (vii) the starting characteristics of the lamps are accomplished by using a mixture of Xenon, Argon, Krypton and  85 Kr gases.  
         [0042]    Referring to FIGS.  1  to  7  and  11 , the above design parameters may be categorized as including one or more of the following:  
         [0043]    (1) Design space limits for arc tube geometry;  
         [0044]    (2) Electrode feedthrough construction and design limits;  
         [0045]    (3) Composition range of iodide salts for achieving desired photometric properties (CCT=3800-4500K, CRI=85-95, MPCD=±10, luminous efficacy of 85-95 lumens/watt); and  
         [0046]    (4) Buffer gas composition and pressure range.  
         [0047]    An especially important aspect of the invention lies in the discovery of the parameter limits within which the whole product family having a power of 150W to 1000W, regardless of the specific rated power, has a lumen maintenance of &gt;80% at 8000 hours (see FIG. 11 for an example); color temperature shift &lt;200K from 100 hours to 8000 hours; and a lifetime in a range of 10,000 hours to 25,000 hours.  
         [0048]    Design Space for Arc Tube Geometry  
         [0049]    The arc tube geometry is defined by a set of parameters best illustrated in FIGS.  1  to  5  and FIG. 9 which also illustrates major parameters used. As seen in FIGS. 1 and 9, the arc tube body inner length (IL) is determined by lamp power. The upper and lower limit of IL for any given lamp power between 150W and 400W can be found in FIG. 1.  
         [0050]    The arc tube body inner diameter (ID) is also a function of lamp power. The upper and lower limits of the ID for any given lamp power from 150W to 400W are shown in FIG. 2.  
         [0051]    One of the common characteristics of this higher wattage MasterColor® lamp family is that the aspect ratio of the arc tube body is higher than that of the lower wattage (30-150W) Philips MasterColor® lamps, which is about 1.0. For any given lamp power for the lamps of the present invention, the aspect ratio (IL/ID) falls into a range of 3.3-6.2. The geometric design space is shown in an IL-ID plot in FIG. 3. The shaded space shown in FIG. 3 is the general design space which does not specify lamp power.  
         [0052]    How each design is compared with others of different rated powers is measured by “wall loading”. Wall loading is defined as the ratio of power and the inner surface area of arc tube body, in a unit of W/cm 2 . In FIG. 4, the upper line is the wall loading value as if the IL and ID are both at their lower limits for the power, therefore the inner surface area is the minimum and wall loading is at maximum. The lower line is the wall loading level as if both IL and ID are at upper limits, making the surface area the maximum and wall loading minimum. Any other designs should have a wall loading range between 23-35W/cm 2 , as indicated by the individual points inside the shaded area. Across the power range of 150W to 400W, the wall loading level remains fairly constant.  
         [0053]    Generally, arc tubes for higher lamp power require a thicker wall, in accordance with the larger volume. The limits of the wall thickness are specified in FIG. 5.  
         [0054]    Electrode Feedthrough Construction and Design Parameters  
         [0055]    Electrodes for conducting current and acting alternatively as cathode and anode for an arc discharge are constructed specifically for the ceramic arc tubes. FIGS. 9 and 10 give the details of the components and their relative positions in the arc tube and show the preferred embodiments of the arc tube  20  having a four-part and a three-part feedthrough, respectively, in which electrodes  30 ,  40  each have a lead-in  32 ,  42  of niobium which is sealed with a frit  33 ,  43 , a central portion  34 ,  44  of molybdenum/aluminum cermet, a molybdenum rod portion  35 ,  45  and a tungsten tip (rod)  36 ,  46  having a winding  37 ,  47  of tungsten and/or in which electrodes  30 ,  40  each have a lead-in  32 ,  42  of niobium which is sealed with a frit  33 ,  43 , a central portion  34 ,  44  of molybdenum/aluminum cermet, and a tungsten tip (rod)  36 ,  46  having a winding  37 ,  47  of tungsten. Preferably, each joint connecting two feedthrough components is welded by a laser welder. Although the three-part feedthrough structure is similar to those used in the lower wattage Philips MasterColor® lamps, the preferred design parameters for constructing the feedthroughs for larger current are given here.  
         [0056]    The primary design parameters for feedthroughs include electrode rod diameter and length as illustrated in FIGS. 6 and 7 which indicate the limits for rod diameter and rod length, versus lamp current.  
         [0057]    Preferably additional parameters are present for the preferred embodiments of the feedthrough construction and include (1) the tip extension of the electrode is in the range of 0.2-1.0 mm, (2) the tip-to-bottom (ttb) distance, i.e. the length of electrode indise the tube arc body, is in a range of 1 mm to 4 mm and generally increases with power, (3) cermet should contain no less then about 35 wt. % Mo, with a preferred Mo content of no less than about 55 wt. % with the remainder being Al 2 O 3 , and (4) the frit (also known as sealing ceramic) flow should completely cover the Nb rod.  
         [0058]    Thus we have found that the following approximations of PCA arc tube and feedthrough characteristics define design spaces in which the desired lamp power may be selected from the parameters and vice versa:  
                                           TABLE I                                   IL/ID   Wall   Wall   Rod   Rod       Power   IL   ID   Aspect   Loading   Thickness   Diameter   Length       W   mm   mm   Ratio, mm   W/cm 2     mm   mm   mm                   150   26-32   5-7   3.3-6.2   20-35   0.8-1.1   0.4-0.6   3-6        200   27-32   6.5-7.5   3.3-6.2   25-30   0.85-1.2   0.4-0.6   4-8        250   28-34   7.5-8.5   3.3-6.2   25-35   0.9-1.3   0.7-1.0   6-10       300   30-36   8-9   3.3-6.2   25-37   0.92-1.4   0.7-1.0   6-10       350   33-40   8.5-10    3.3-6.2   24-40   0.98-1.48   0.7-1.1   6-11       400   36-45   8.5-11    3.3-6.2   22-40   1.0-1.5   0.7-1.1   6-11                  
 
         [0059]    Preferably also (1) the tip extension of the electrode is in the range of 0.2-1.0 mm, (2) the tip-to-bottom (ttb) distance is in a range of 1 mm to 4 mm and generally increase with power, (3) the cermet contains no less then about 35 wt. % Mo, with a preferred Mo content of no less than about 55 wt. % with the remainder being Al 2 O 3 , and (4) the frit (also known as sealing ceramic) flow completely covers the Nb rod.  
         [0060]    Composition of Metal Halide Salt Mixture  
         [0061]    The salt mixture is specially designed for the power range and arc tube geometry used for this product family. The following table gives the nominal composition of the salt mixture wherein the total composition is 100%:  
                                       TABLE II                       Salt   NaI   TlI   CaI 2     DyI 3     HoI 3     TmI 3                     Wt. %   6-25   5-6   34-37   11-18   11-18   11-18                  
 
         [0062]    Buffer Gas Composition and Pressure Range  
         [0063]    The filling of the discharge vessel includes 1-5 mg Hg. The mercury content is similar to that of Philips&#39; Alto® Plus lamps, i.e. about &lt;5 mg and the lamps of the invention have passed the TCLP test and thus are environmentally friendly. In addition, the lamps also contain 10-50 mg metal halides in a ratio of 6-25 wt % NaI, 5-6 wt % TlI, 34-37 wt % CaI 2 , 11-18 wt % DyI 3 , 11-18 wt % HoI 3 , and 11-18 wt % TmI 3 . The arc tube is also filled with a mixture of noble gases for assisting lamp ignition. The composition of the gas is a minimum of about 99.99% of Xenon and a trace amount of  85 Kr radioactive gas but may use a mixture of Ar, Kr and Xe instead of pure Xe as a possible alternative. Pure xenon is preferred since the lamp efficacy has been indicated to be higher when compared to lamps with Ar. Additionally, the breakdown voltage of lamps utilizing xenon is higher than that of lamps with Ar, and the wall temperature of lamps is lower than that of lamps with Ar. The room temperature fill pressure of this product family is preferably in a range of about 50 torr to about 150 torr.  
         [0064]    Molybdenum Coil  
         [0065]    As discussed above, for reducing the risk of non-passive failure, a molybdenum coil wrapped around the arc tube and around the extended plugs is used as disclosed in our U.S. patent application Ser. No. ______ (Disclosure No. 701713) filed of even date herewith as a divisional application of this application for “Coil Antenna/Protection For Ceramic Metal Halide Lamps”.  
         [0066]    This application discloses a Mo coil antenna wrapped around a PCA arc tube and around at least a portion of the extended plugs. The coil antenna serves as an antenna for starting or ignition, provides good capacitive coupling for ignition, has no adverse effect on the efficacy or lifetime properties of the lamps, and also provides mechanical containment of particles in the event of arc tube rupture.  
         [0067]    The product family will have a wide range of usage in both indoor and outdoor lighting applications. The primary indoor applications include constantly occupied large-area warehouse or retail buildings requiring high color rendering index, high visibility and low lamp-to-lamp color variation. Outdoor applications include city street lighting, building and structure illumination and highway lighting.  
         [0068]    It will be understood that the invention may be embodied in other specific forms without departing from the spirit and scope or essential characteristics thereof, the present disclosed examples being only preferred embodiments thereof.