Multiple, parallel filament lamp

Details Multiple, parallel filament lamp Multiple, parallel filament lamp

2002-05-15

2004-08-10

Patel, Nimeshkumar D. (Department: 2879)

Electric lamp and discharge devices

With support and/or spacing structure for electrode and/or...

For filament

C313S271000, C313S273000, C315S046000, C315S047000, C315S064000

Reexamination Certificate

active

06774546

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX
Not Applicable.
BACKGROUND OF THE INVENTION
The present invention relates to lamps. More particularly, the present invention relates to multi-filament lamps. Generally, inside the glass envelope or bulb of a lamp, a filament, which is usually made from tungsten, is extended between two power terminals. Basically, the filament is a resistor that heats up when a voltage is applied across the terminals, and normally operates at temperatures of about 2500° C. in incandescent lamps, and at significantly higher temperatures in halogen lamps. At these high temperatures the filament gives off a substantial amount of thermal radiation, which includes a considerable amount of visible light (when compared to the amount of visible light given off at lower operating temperatures). Also, these high temperatures cause some of the tungsten molecules to evaporate off of the filament and condense onto the glass bulb. This causes the filament to become thinner and more resistant to current flow, causing the thinner filament portion to become even hotter, and leading to further evaporation. Similarly, fabrication inefficiencies can also cause thin spots to be formed on the filament during manufacturing. Eventually, the loss of tungsten molecules will cause the filament to fail or “burnout” and, due to the economics involved, an inoperable lamp is generally replaced and disposed of without expending any effort toward repair.
To extend the life of electric bulbs (or lamps), various methods have been employed to minimize, or compensate for, the loss of filament molecules. For example, incandescent bulbs are oftentimes filled with an inert gas—instead of operating the filaments in a partial vacuum inside of the bulb. Besides preventing filament combustion, the inert gas is a source of molecules that are used to collide with the evaporated tungsten molecules. Desirably, prior to the tungsten molecules condensing on the inside of the glass bulb, these collisions will redirect the tungsten molecules back toward the filament where they may be recovered. As another example, halogen lamps minimize the loss of tungsten filament molecules through the use of a process known as halogen recycling. Generally, halogen recycling is a chemical reaction that collects previously free tungsten molecules from the inside surface of the glass and then, due to the high temperature of the filament, re-deposits them on the filament.
A different approach to extending lamp life makes use of more than one filament. In this regard, multi-filament lamps have been described in a number of patents, for example, U.S. Pat. No. 4,553,066, issued to Fields et al. on Nov. 12, 1985, describes a multi-filament lamp that uses longitudinally extending filaments and a wire grid to help ensure that a failed filament does not break free and interfere with an operable filament. This invention, however, supplies power to each filament separately and, therefore, uses a separate lead-in wire for each filament, e.g., a three-filament lamp will require three lead-in wires and a common wire. Since the amount of time that a lamp is energized is the main cause of lamp failure, and since all of the filaments are simultaneously operating in this invention, lamp life may not be appreciably extended. In the U.S. Pat. No. 5,061,879, issued to Munoz et al. on Oct. 29, 1991, another multi-filament lamp is described. This invention, however, does not power each filament at the same time, but, on the other hand, this invention is only a two-filament lamp and it requires the use of an external control module for switching the second filament on after the first filament fails.
Furthermore, while light bulbs generally last for several hundred hours before burning out, some light bulbs will last much longer and are commonly referred to as “long life” bulbs. Generally, long life bulbs are made with a single, heavier gauge, filament and have a reduced resistance to current flow, but these bulbs are not as economical as standard bulbs and like standard bulbs must be replaced as soon as their single, heavier gauge filament fails. Thus, a need still remains for an economical way to extend the life of a light bulb.
SUMMARY OF THE INVENTION
According to its major aspects and briefly recited, the present invention is light bulb having at least two groups of filament segments and at least three filaments wherein, each group of filaments can be classified as primary filaments, which are a part of a series connected electrical circuit and, therefore, capable of initially being energized to provide illumination; backup (or secondary, or primary backup) filaments, which bypass a failed, i.e., open circuited, primary filament and become a part of the series circuit and, therefore, capable of being energized to provide illumination; and/or other subsequent level filaments (or subsequent level backups), which, in turn, bypass a failed, i.e., open circuited, prior level filament and become a part of the series circuit and, therefore, subsequently capable of being energized to provide illumination. Generally, filaments are fabricated by forming tungsten into a very fine wire having a diameter of about 50 microns, and then winding this wire into a double spiral coil and attaching the ends of the filament to power leads, which are attached to a support structure made of an insulator such as glass. Oftentimes, when a filament burns out, i.e., open circuits, it does so in one place along the length of the filament while the remainder of the filament is still usable, if this remaining operable portion could be connected back into an operable filament circuit. By using a two-filament group embodiment, containing a total of three filaments, as an example, but not as a limitation, two of the three filaments are primary filaments and are initially capable of providing illumination when the lamp is energized, and the other filament is a backup (or secondary) filament to one of the primary filaments. Since any of the embodiments of the present invention can be made to use filaments having the same, or different, electrical and/or luminosity characteristics, in this example it is assumed that one of the primary filaments is a lower gauge filament, is operating hotter, and/or is otherwise more likely to fail prior to the other primary filament. The secondary filament, in this example, through the use of shunts is connected in parallel with the more likely to fail filament. The shunts may include, but are not limited to, devices that are made of an oxidized metallic material, which does not become conductive until a breakdown voltage greater than the material's breakdown voltage rating is applied to it. In normal operation this magnitude of voltage, i.e., greater than the breakdown voltage rating, is not applied across the shunts, but upon failure of the primary filament to which the shunts are attached (which, in this example, is the more likely to fail filament) a voltage greater then the breakdown voltage rating is applied across the shunts and the backup filament becomes electrically connected in series with the operable primary filament, i.e., the backup filament bypasses the failed primary filament. Similarly, other embodiments of the present invention lamp may include, but are not limited to, those that have a separate backup filament across each of the primary filaments, which would allow for a separate backup filament to be used to bypass each failed primary filament, and/or at least one tertiary filament across at least one of the backup filaments, which will be used to bypass a failed, i.e., open circuited, backup filament and, therefore, become a part of the series filament circuit and, therefore, capable of being energized to provide illumination.
The primary filament segments are connected in series and can be positioned in an essentially straight con

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