Patent Application
20080238321
This invention relates to arc lamps.
Arc lamps are glass or quartz vessels that house electrodes that are used to produce an electrical arc for illumination purposes. The vessel is usually filled with a gas such as xenon or mercury. Sometimes various other elements are added to obtain an enhanced color temperature or the electrical arc such as sodium. The electrodes of the arc lamp are usually sealed by pinching the glass or quartz from the vessel around each electrode during a heat sealing process. The area where the electrodes have been sealed by the pinching process is commonly referred to as a “pinch”.
It is important during operation of the arc lamp that each pinch not be allowed to rise above a certain temperature. Allowable temperatures for the pinch range from three hundred degrees centigrade to four hundred and fifty degrees centigrade. If the temperature of a lamp pinch is allowed to rise over the highest operating temperature the pinched area can start to oxidize rapidly in the area where the sealing of the electrode takes place. The oxidization of the pinch area at the electrode causes a catastrophic seal leak and can cause the vessel to leak out the filler gas sometime resulting in an explosion. U.S. Pat. No. 3,377,498 to Koury et al describes a high pressure arc lamp, and is incorporated by reference herein. U.S. Pat. No. 3,723,784 to Sulcs et. al. is incorporated by reference herein, and describes a high pressure sodium lamp with “heat reflecting shields surrounding its electrodes”. Sulcs describes “Thus the seal temperature and the cold spot temperature can be controlled by adjusting the width of the foil”. U.S. Pat. No. 4,721,887 to Inukai et al, incorporated by reference herein, describes a method of creating a pinched arc lamp seal.
It has been found that direct radiation and reflected radiation emitted from the arc created by the arc lamp can be absorbed by the external electrode connecting leads. It is desirable to reduce the absorbed radiation of the external electrode connecting leads in order to reduce the temperature of the lamp pinch.
A novel means of altering the absorbing properties of the external electrode connecting leads of an arc lamp is disclosed. The electrode leads may be coated with a light reflecting ceramic paste to reduce the absorption of light emitted by the arc.
In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of embodiments of the present invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the present invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce the desired results.
Radiation emitted from the arc 110 is also emitted in the direction of arrow 139a that reflects off of the left hand side of the reflector 160a in the direction of arrow 140a. Radiation emitted from the arc 110 is also emitted in the direction of arrow 139b that reflects off of the right hand side of the reflector 160b in the direction of arrow 140b. Often an optical device 150 such as a hot mirror that reflects infrared energy is placed in the path of the emitted radiation from the arc 110 as shown by arrows 140a and 140b. The optical device 150 could also be a lens, a protective window or an integrator as known in the art. The optical device 150 will often reflect some of the radiation that is collected by the reflector 160 from the arc lamp 100 in the direction of arrow 144. The radiation reflected off of the optical device 150 in the direction of arrow 144 casts itself upon the upper external electrode connecting lead 113a and the top section 116a of upper external electrode connecting lead 116 and thus raises the temperature of the upper external electrode connecting leads 113a and 116. The upper external electrode connecting lead 113a is often made from a metal such as tungsten or molybdenum or another metal that absorbs the radiation reflected from the optical device 150 in the direction of arrow 144. Absorption of the reflected radiation shown in the direction of arrow 114 by the upper external electrode connecting lead 113a, the top section 116a of the upper external electrode connecting lead 116 and absorption of the direct radiation shown in the direction of arrow 124 by the center section 116b of the upper external electrode connecting lead 116 raises the temperature of the upper external electrode connecting leads 113a and 116. When the temperature of the upper connecting leads 113a and 116 are raised the operating temperature of the pinch 104 also rises. This is an undesirable since management of the maximum pinch temperature of the pinch 104 is important for obtaining maximum life time of the arc lamp 100.
The reflective material used for upper external electrode connecting lead 213a and center portion 216b of external upper electrode lead 216 may be any material that can significantly reflect the radiation emitted in the direction of arrows 144 and 124. The center portion 216b is the portion of the upper external electrode connecting lead 216 that is shown routed in proximity to the bulb 108. The reflective shrouding of the modified center section shown as 216b of the upper external electrode connecting lead 216 reflects a large portion of the direct radiation in the direction of arrow 124 from the arc 110. In a preferred embodiment of the invention the reflective material used as a shroud is a ceramic paste that is bright white in color and can withstand a high temperature. The white ceramic paste is coated upon the upper external electrode connecting leads 113a and 116, shown in
The white ceramic paste is one method of reducing the absorption of the upper external electrode connecting leads 213a and 216. A white ceramic tube may also be used over the upper external electrode connecting leads 213a and 216 in the areas where direct and reflected radiation are present to reduce absorption of the direct and reflected radiation. Any radiation reflecting material that reflects the radiation created by the arc 110 may be applied to the upper external electrode connecting lead 113a and areas 116a and 116b or lead 116, to form lead 213a, and areas 216a, 216b, and lead 216. Alternatively the upper external electrode connecting leads 213a and 216 may be constructed of a conducting material that is also reflective to the energy emitted by the arc 110.
