Par lamp with reduced lamp seal temperature

#The invention relates to electric lamps and particularly to electric lamps enclosed in a reflector. More particularly the invention is concerned with a reflector lamp (PAR) with a ceramic metal halide lamp capsule with a reduced lamp capsule seal temperature.

#Ceramic lamp envelopes with modem metal halide seals have developed a new class of metal halide lamps (Geven et. al. in U.S. Pat. No. 5,424,609 and by Carleton et. al. in J. Ill. Eng. Soc. P139-145, Winter 1996 (Proc. Of IESNA Annual Conference)). These lamps contain metal halide fill chemistries, and two electrodes. A high voltage pulse between the electrodes is used to ignite the lamp. Normal current and voltage is then applied through the electrodes to excite the enclosed gas and fill materials to a plasma state. Typical fills include rare earth halides with various other additives including thallium halide and calcium halide, in addition to an inert starting gas such as argon or xenon.

#The ceramic arc tube is often jacketed in another envelope, called an outer jacket, to protect the inner arc tube from the air. Many of the lamp parts, especially niobium electrical in-leads, oxidize rapidly if exposed to air at the lamp operating temperatures, causing the lamp to fail. These outer jackets are usually thermally isolated from the arc tube by construction and contain a vacuum or are filled with a partial pressure of an inert gas and a getter material, for example a zirconium and aluminum compound, to getter oxygen and hydrogen.

#FIG. 1 shows a schematic cross-sectional view of a preferred embodiment of a lamp assembly with an internal black top coating.

#FIG. 2 shows a schematic cross-sectional view of a preferred embodiment of a lamp assembly with a light absorbing shell material.

#FIG. 3 shows a schematic cross-sectional view of a preferred embodiment of a lamp assembly with an external black top coating.

#FIG. 1 shows a schematic cross-sectional view of a preferred embodiment of a lamp assembly with an internal light absorbing coating. The preferred PAR lamp assembly 10 comprises a light source 12 having two sealed electrodes 14, 16 defining a lamp axis 18; a concave ceramic shell 20 having an internal reflective surface 22. The shell 20 further has a neck 24 defining a neck cavity 26 and a reflector axis 28. The neck 24 is provided with an electrical connection 30 and a mechanical support for the light source 12. The shell 20 surrounds the light source 12 to reflect light from the light source 12 to a field to be illuminated during lamp operation. The preferred light source 12 and reflector 20 are oriented with the lamp axis 18 to be substantially co-axial with the reflector axis 28, and at least a portion of at least one of the electrodes 14, 16 extends in the neck cavity 26, and a region with a substantially non-transmissive, light absorbing layer 32.

#The light source 12 may be any light source, although the value comes from protecting a particularly hot light source such as a high intensity discharge (HID) light source held in an outer jacket. The preferred light source is double ended and has with a first electrode 14 extending approximately axially with respect to the light source axis 20, and a similar second electrode 16 similarly extending axially from the light source. The first electrode 14, and second electrode 16 then define a lamp axis 18. Typical double-ended high intensity discharge lamps are made from quartz, hard glass or ceramic and are tubular in shape. Ceramic lamps are of particular interest here, but the concept can be applied to other lamps also.

#The concave ceramic shell 20 has an internal reflective surface 22 formed thereon, for example an aluminization or dichroic coated layer. The preferred reflector is a body of revolution about a reflector axis 28. The reflector may have a parabolic, elliptical or similarly prescribed surface that may be smooth, faceted or otherwise shaped to reflect light from the light source 12 in preferred directions, to yield a desired beam pattern. The shell 20 further extends from the region of the reflective surface 22 towards a narrower neck 24 defining a neck cavity 26. The neck 24 is provided with an electrical connection or connections 30 for powering the light source, and a mechanical support or supports, which may be the same as the electrical connections. The mechanical supports hold the light source 12 in a preferred position relative to the shell 20. The light source 12 generally faces the reflective surface 22 so that light from the light source 12 is reflected to a field to be illuminated during lamp operation. The preferred light source 12 and reflector 20 are oriented along the lamp axis 18 to be substantially co-axial with the reflector axis 28. At least a portion of the sealed lead for one of the electrodes, for example the sealed lead for electrode 14, extends in the neck cavity 26, in the lamp seal region 34.