Abstract:
A single-ended glass halogen lamp includes an infrared reflecting shroud surrounding a lamp filament which reflects infrared energy back to the lamp filament to heat the filament and improve overall lamp efficiency. The shroud is supported within the lamp enclosure by the electrical leads which connect the lamp filament to a source of electricity. The optical interference filter is preferably a tantala-silica coating formed on an exterior of an ellipsoidal shaped shroud.

Description:
This application claims the benefit of Provisional No. 60/061,513, filed Oct. 10, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to the field of glass halogen lamps and, more particularly, to a glass halogen lamp with an internally mounted shroud for reflecting infrared radiation back to the lamp filament. 
     Thin film optical interference coatings, known as interference filters, including alternating coating layers of two or more materials having different refractive indices, are used in the illumination field to selectively reflect and/or transmit light of different wavelengths. Interference coatings can be used to transmit various portions of the electromagnetic spectrum, such as visible light, while reflecting other portions of the electromagnetic spectrum, such as ultraviolet or infrared radiation. These interference coatings are used in the lamp industry to coat Reflectors and/or lamp envelopes to achieve desirable illuminance patterns and to filter out undesirable energy. 
     Thin film optical coatings have been used on lamp enclosures to improve the illumination efficiency of incandescent lamps by reflecting infrared energy emitted by a filament back to the filament while transmitting the visible light portion of the electromagnetic spectrum emitted by the filament through the enclosure. The reflected infrared radiation heats the filament and reduces the amount of electrical energy required to maintain the filament operating temperature. Thus, the infrared reflective coating increases the illumination provided by a lamp for the same amount of energy input. The infrared reflective optical coatings can also improve the efficiency of an arc lamp in substantially the same manner. 
     One example of the use of an optical interference coating for reflecting infrared radiation in a halogen lamp is described in U.S. Pat. No. 5,138,219. The thin film infrared reflecting, optical interference filter is coated onto the outer surface of the lamp envelope to reflect infrared energy back to the filament. Although this glass halogen infrared reflecting lamp provides a benefit of improved lamp efficiency, it is relatively expensive to manufacture due to the large amount of coating material used to coat the enclosure and due to difficulties in mounting the lamp within the parabolic reflector. 
     It would therefore be desirable to provide an efficient lamp with an infrared coating which is less expensive to manufacture and easier to mount than the known lamps. 
     SUMMARY OF THE INVENTION 
     The present invention contemplates a new and improved single-ended glass halogen lamp which takes advantage of an infrared coating for maximum energy savings and also provides lower cost manufacturing than the known lamps. 
     In accordance with the present invention, a glass halogen lamp includes a lamp filament, a light transmissive lamp enclosure surrounding the lamp filament, and first and second electrical leads electrically connected to opposite ends of the lamp filament and both extending from a first side of the lamp enclosure. An ellipsoidal shroud is positioned about the lamp filament between the filament and the enclosure and a light-transmissive, infrared energy reflecting coating is formed on the ellipsoidal shroud to reflect infrared energy generated by the filament back to the filament to improve an efficiency of the lamp. 
     In accordance with a more limited aspect of the invention, at least one of the first and second electrical leads functions to support the ellipsoidal shroud within the enclosure. 
     In accordance with a further aspect of the present invention, an electrical lamp includes an electric light source, a shroud coated with an optical interference coating which reflects infrared radiation and transmits visible light, the shroud surrounding the light source and reflecting the infrared radiation emitted by the light source back to the light source, a hermetically sealed envelope surrounding the shroud, and an inert gas disposed within the envelope and surrounding the shroud and filament. 
     The principal advantages of the invention are energy savings provided by the infrared reflecting coating, low cost manufacturing due to the shroud and the single-ended lamp configuration, and ease of mounting. 
     Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangements of parts, preferred embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof, and wherein: 
     FIG. 1 is a side cross-sectional view of a lamp according to a first embodiment of the invention; 
     FIG. 2 is a side cross-sectional view of a second embodiment of the lamp according to the present invention; and 
     FIG. 3 is a partial cross-sectional view of the lamp of FIG. 1 mounted in a parabolic reflector. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings wherein the showings are for the purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same, FIG. 1 shows a single-ended glass halogen lamp  10  with an internally mounted ellipsoidal shaped shroud  12  surrounding a lamp filament  14  to provide maximum energy savings. 
     As illustrated in FIG. 1, the ellipsoidal shroud  12  and filament  14  are surrounded by an enclosure  16  formed of a light transmissive quartz or high temperature aluminosilicate glass which is capable of withstanding high temperatures of about 800° C. The enclosure  16  includes a base  18  through which the two inner lead wires  20 ,  22  extend. The inner lead wires  20 ,  22  are hermetically sealed in the base  18  and connect the filament  14  to the outer leads  24 ,  26 . Preferably, the inner leads  20 ,  22  are made of a suitable refractory material such as molybdenum or tungsten and are electrically and mechanically connected to the outer leads  24 ,  26  by a suitable welding method. 
     The enclosure  16  contains an inert gas, such as argon, xenon, or krypton along with a minor amount (i.e., less than 10%) of nitrogen, one or more halogen compounds such as methyl bromide, dibromomethane, dichlorobromomethane, and the like, and a gettering material such as phosphorous. 
     The shroud  12  includes an ellipsoidal body portion connected to two cylindrical end portions  32 ,  34  which are open to the interior and the exterior of the shroud. The lamp filament  14  is mounted within the shroud  12  such that opposite ends  36 ,  38  of the filament are positioned at or near the foci of the ellipsoid. The position of the lamp filament  14  between the foci of the ellipsoid provides maximum energy recovery by focusing the reflected infrared energy along the length of the filament. 
     The ellipsoidal shroud  12  is mounted within the enclosure  16  between the inner lead wires  20 ,  22  by notches  40  formed in the cylindrical end portions  32 ,  34  of the shroud. The shorter of the two inner leads  20  is received in the notches  40  on the lower end  34  of the shroud while the longer of the two inner leads  22  is received in the notches  40  in the upper end  32  of the shroud. In addition to supporting the shroud, the inner lead wires  20 ,  22  cross over the open ends of the ellipsoidal shroud  12  and, at that point, are electrically and mechanically connected to the vertically extending filament leads  42 ,  44 . The filament leads  42 ,  44  are preferably welded to the filament  14  by plasma welding or laser welding. The inner lead wires  20 ,  22  are specially shaped to support and maintain the relative position of the quartz shroud  12  with respect to the filament  14 , and to maintain the position of the filament and shroud in substantially the center of the enclosure  16 . 
     The ellipsoidal shroud is preferably a quartz shroud coated with a light transmissive, infrared reflecting filter coating of the type disclosed in U.S. Pat. No. 5,138,219, which is incorporated herein by reference. Preferably, the infrared reflecting coating includes alternating layers of SiO 2  and Ta 2 O 5  applied employing an LPCVD coating process. The use of the coated shroud  12  to reflect infrared energy and increase the temperature of the lamp filament improves lamp efficiency by as much as 40%. The shroud  12  according to the present invention may be coated either on an interior or an exterior surface. However, the coating is more easily applied to the exterior surface of the shroud. 
     The lamp  10  illustrated in FIG. 1 is assembled in a parabolic reflector  50  in FIG.  3 . The lamp  10  is mounted into the bottom portion of the parabolic glass reflector  50  by means of conductive mounting legs  52  which project through seals at the bottom of the glass reflector  50 . The mounting legs  52  are electrically and mechanically attached to the exterior leads  24 ,  26  of the lamp  10  by suitable means, such as welding. The lamp base  54  is a standard screw base for screwing the completed reflector and lamp assembly into a suitable lamp socket. The lamp base  54  is crimped onto the bottom portion of the glass reflector  50 . A glass or plastic lens or cover  56  is attached or hermetically sealed by adhesive or other suitable means to the opposite end of the reflector  50 . 
     An alternative embodiment of the lamp  10   a  according to the present invention is illustrated in FIG. 2 in which the ellipsoidal shroud  12   a  is mounted within the enclosure  16   a  in an alternative manner. The long lead  22   a  according to this embodiment includes two wire ring supports  62  fixed to a vertical portion of the long lead and positioned at a top and a bottom of the shroud  12   a . The wire ring supports  62  are positioned around the cylindrical end portions  32   a ,  34   a  of the shroud to support the shroud in a fixed position with respect to the filament  14   a  and the enclosure  16   a . The short lead  20   a  is connected to the filament lead  42   a  and together with the long lead  22   a  supports the filament  14   a  within the shroud. 
     Although the present invention has been described with respect to a glass halogen lamp with a coil-shaped filament  14 ,  14   a , the coated ellipsoidal shroud  12 ,  12   a , according to the present invention, may also be used with filaments of other shapes. In addition, the ellipsoidal shroud may be used to improve the efficiency of an arc discharge lamp. In an arc discharge lamp, the electrodes of the arc will be positioned within the shroud in place of the filament with the electrodes at or near the foci of the ellipsoidal shroud. 
     The advantages of the present invention include an efficiency which is improved by as much as 40% over a similar halogen lamp without an infrared reflecting coating. The present invention also provides advantages over known lamps in which the entire enclosure is coated with an infrared reflecting coating in that cost savings are achieved from more efficient use of the coating on the smaller shroud. In addition, more shrouds can be coated in a single coating process due to the smaller size of the shroud than if the entire enclosure is coated, thus throughput is increased. Finally, an additional cost savings is provided by the ability to modify existing equipment to make and mount the new lamp within the parabolic reflector instead of building new equipment. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon a reading and understanding of this specification. The invention is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.