RAPID START FLUORESCENT LAMP WITH A BIMETAL ELECTRODE DISCONNECT SWITCH

Abstract: A rapid start fluorescent lamp having a glass envelope with a phosphor coated inner surface, a low pressure noble gas fill and an electrode at each end includes an electrode disconnect switch having a bimetal switch with a glass bottle and normally closed at room temperature and open at higher temperatures. The bottle is maintained at vacuum or is filled with a noble gas and the bimetal switch has a meltable bypass electrically conductive member shunted thereacross during manufacture of the lamp and removable thereafter.

Description: RAPID START FLUORESCENT LAMP WITH A BIMETAL ELECTRODE DISCONNECT SWITCH TECHNICAL FIELD This invention relates to rapid start fluorescent lamps and more particularly to rapid start fluorescent lamps having a bimetal electrode disconnect switch affixed to one electrode for discontinuing heater current flow upon effecting conductivity of the lamp. BACKGROUND ART In the fluorescent lamp art, both preheat type and rapid start type fluorescent lamps are commonly encountered. In the preheat type of fluorescent lamp, heater current flows through the electrode only during lamp ignition whereupon an external voltage sensitive starter opens the heater current circuit and discontinues heater current flow. In contrast. the rapid start fluorescent lamp normally has a constant heater current flow through each electrode both during ignition and operation of the lamp. Unfortunately. heater current flow during operation of the rapid start fluorescent lamp is lost powder which obviously reduces the operational efficiency of rapid start fluorescent lamps. Numerous suggestions have been made for enhancing efficiency of rapid start fluorescent lamps. For example, U.S. Patent Nos. 4,052,687; 4,097,779; 4,114,968; 4,156,831 and 4.171.519. all assigned to the Assignee of the present application, suggest numerous configurations for enhanced operation of rapid start fluorescent lamps. Generally. each provides a thermally responsive circuit breaker suitable for use in discontinuing heater current upon operation of the fluorescent lamp. However, it has been found that problems still exist. For example, it has been found that a problem occurs whenever the thermally responsive circuit breaker extends in a direction parallel to the electrode of a lamp but for a distance greater than the length of the electrode. Thereupon, positioning the lamp envelope properly is encumbered because the envelope tends to undesirably contact the circuit breaker when the circuit breaker and lamp electrodes are being inserted into the envelope. Such an encounter is obviously undesirable, and especially so in a high production manufacturing process. In another aspect, it has been found that positioning of the circuit breaker too close to the electrode has a deleterious effect upon the life span of the fluorescent lamp. More specifically, closely spacing the circuit breaker to an electrode generating heat tends to significantly reduce the life span of the fluorescent lamp wherein the electrode is located. In still another respect of the invention, it has been found that the consistency and repeatability of operation of a circuit breaker disposed within a discharge lamp can be adversely affected when left unprotected from the environment within the discharge lamp. In other words, a bimetal switch means placed nearby an activated electrode within a discharge lamp may be deleteriously affected when protection is not provided such that the bimetal switch surfaces are not isolated from the electrode discharge area. OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide an enhanced rapid start fluorescent lamp. Another object of the invention is to improve the operating efficiency of a rapid start fluorescent lamp. Still another object of the invention is to improve the capabilities for manufacture of the above-described enhanced rapid start fluorescent lamp. A further object of the invention is to reduce the energy requirements during operational use of a rapid start fluorescent lamp. These and other objects, advantages and capabilities are achieved in one aspect of the invention by a rapid start fluorescent lamp having an envelope with a phosphor-coated inner wall surface, a low pressure fill gas, an electrode within each end of the envelope and a pair of electrically conductive leads passing through each end of the envelope for coupling an electrode to an energizing source wherein an electrode disconnect switch has a bimetal switch means normally closed at room temperature and open at a predetermined temperature higher than room temperature and spaced at least a millimeter from at least one of the electrodes. In another aspect of the invention, a rapid start fluorescent lamp has an electrode disconnect switch therein which includes a bimetal switch means within a glass bottle with a pair of electrical conductors connecting the bimetal switch means to an electrode within-the lamp and to an electrical lead passing through the discharge lamp to an energizing source. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view, partly in section, of one end of a rapid start fluorescent lamp prior to processing; FIG. 2 is an elevational view, partly in section, of one end of a rapid start fluorescent lamp of the invention: and FIG. 3 is a chart illustrating the relative life of a 40-watt rapid start fluorescent lamp with regard to the average or mean distance of an electrode disconnect switch from the lamp electrode. BEST MODE FOR CARRYING OUT THE INVENTION lor a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in conjunction with the accompanying drawings. Referring to FIGS. 1 and 2 of the drawings, a rapid start fluorescent lamp suitable for processing includes an elongated glass envelope 5 having a coating 7 of phosphor on the inner wall surface of the envelope 5. A glass stem member 9 is sealed into the end of the envelope 5 and includes a pair of electrical leads 11 and 13 sealed therein and passing therethrough. An end cap 15 is telescoped over and attached to the end of the glass envelope 5 and includes a pair of pins 17 and 19 electrically connected to a portion of the electrical leads 11 and 13 and formed to provide electrical connection to an external potential source (not shown). Moreover, the envelope 5 has a gas fill therein selected from the group consisting of argon, xenon, krypton, neon, helium and combinations thereof. Within the envelope 5, an electrode 21 has one end thereof connected to one of the electrical leads 13 and a longitudinal axis which extends in a direction substantially normal to the direction of the electrical leads 11 and 13. The electrode 21, which is often referred to as a heater or cathode, is of a well known type used in rapid start fluorescent lamps and includes a coating thereon which is usually in the form of alkaline earth oxides applied thereto in the form of carbonates which. upon processing, are converted to oxides. The opposite end of the electrode 21 is connected to the other electrical lead 11 which is, in turn, connected to the pin 17 by way of an electrode disconnect switch 23. The electrical disconnect switch 23 is preferably in the form of a glass bottle 25 having a pair of electrical conductors 27 and 29 sealed into one end. A bimetal switch 31 is located within the glass bottle 25 and connected intermediate the electrical conductors 27 and 29. A meltable bypass member 33 is affixed to the conductors 27 and 29 in shunting relationship to the bimetal switch 31. Moreover, a vacuum or a gas fill of noble gases or nitrogen or combination thereof is contained within the glass bottle 25. Thus, electrical connection between the electrode 21 and the pin 17 is effected by way of the electrical lead 11, the electrical conductors 27 and 29 of the bimetal switch 23 and the bimetal switch 31 or the bypass member 33 as will be explained hereinafter. Alternatively, the electrical disconnect switch 23 may be in the form of a bimetal switch 31 having either a substantially U-shaped or straight configuration which would be located within the lamp envelope. Although a hermetically sealed glass bottle 25 having a gas fill is preferable, the switch 31 may have an insulating cover or be disposed within a bottle merely shielding the switch 31 from the electrode 21. Also, it is conceivable that the electrical disconnect switch 23 could be of a form wherein the electrical conductors 27 and 29 exit from opposite ends of the glass bottle 25. As to manufacture, it is well known that the glass envelope 5 has the glass stem member 9 inserted therein and sealed thereto. Accordingly, it has been found most expedient to position the electrode disconnect switch 23 in a manner such that the switch 23 is located between and does not extend beyond a pair of substantially parallel planes extending in a direction normal to the longitudinal axis of the electrode 21 and intercepting the ends of the electrode 21 Thus, it has been found that the electrode disconnect switch 23 is not normally disturbed when the envelope 5 is telescoped over the electrode 21 since the disconnect switch 23 does not extend beyond a plane normal to the ends of the electrode 21. As to operation of the electrode disconnect switch 23, it is known that the previously-mentioned alkali earth oxides on the electrode 21 are derived from a coating of carbonates during the manufacturing process. Normally, this process is effected by applying current to the electrical leads 11 and 13 in an amount sufficient to raise the temperature of the electrode to about 17009 C. However, the bimetal switch 31, which is normally closed at room temperatures in a 40-watt lamp, tends to operate or open at a temperature in the range of about 140 to 180 C. Thus, the process temperatures employed to bake and seal the envelope 5 to the glass stem member 9 would tend to activate the bimetal switch 31. Moreover, current applied to the leads 11 and 13 would fail to effect the desired 17000 C. temperature of the electrode 21 for processing the carbonates thereon since the bimetal switch 31 is operational and would interrupt the process. In order to achieve this desired processing of the electrode 21 during manufacture, a bypass member 33 of a refractory material, such as molybdenum or stainless steel, is connected across the electrical conductors 27 and 29 of the electrical disconnect switch 23. This bypass member 33 is of a meltable material and in response to an electrical pulse potential, such as a pulse from a 270 microfarad v capacitor charged to 300 D.C., is removed or melted away after processing the carbonates to provide the desired electrode disconnect switch 23 capability. Additionally, it has been found that the position of the electrode disconnect switch 23 with respect to the electrode 21 within the lamp envelope 5 is important. Since rapid start fluorescent lamps may be of different wattages and of a length of 3, 4, 6 or 8-feet for example, it has been found that the electrode disconnect switch 23 should be spaced at least one millimeter from the electrode 21. Also, the electrode disconnect switch 23 should be of a material and configuration to operate at temperatures in the range of about 750 C to 3000 C depending upon the capacity of the lamp and the location of the disconnect switch 23 with respect to the electrode 21. More specifically, it has been found that a normal 4-foot, 40-watt fluorescent lamp preferably has an electrode disconnect switch 23 such that the average spacing, X of FIG. 2, between the switch 23 and the electrode 21 is not less than about 8.0 mm. and not more than about 14.0 mm. Moreover, the temperature necessary to operate the electrode disconnect switch 23 in the above-mentioned 40-watt lamp is in the range of about 1400 C to about 180 C. Finally, it is to be noted that curve A of the comparison chart for a 40-watt rapid start fluorescent lamp of FIG. 3 provides a comparison of relative lamp life in percentages. with the average distance of the electrode disconnect switch 23 from the electrode 21. As can readily be seen, the relative lamp life increases at a relatively rapid rate as the spacing between the disconnect switch 23 and electrode 21 increases. However, this increased lamp life tends to level off at a spacing of about 8.0 mm. Moreover, tests indicate that a spacing between the switch 23 and electrode 21 of greater than about 14.0 mm. in a 40-watt rapid start fluorescent lamp creates problems in achieving the desired temperatures consistent with proper operation of the disconnect switch 23. Thus, there has been provided a rapid start fluorescent lamp which includes an electrode disconnect switch having a capability for effecting desired processing of an electrode as well as disconnection thereof during operational use of the lamp. Also, the electrode disconnect switch is positioned such that interference thereof with the joining of an envelope and stem member is not a problem and provision is made for removing the electrode heating capability during manufacture. While there has been shown and described what is at present considered the preferred embodiments of the invention. it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined by the appended claims.

Claims: CLAIMS WHAT IS CLAIMED IS: 1. A rapid start fluorescent lamp having an envelope with a phosphor-coated inner wall surface, a low pressure fill gas, an electrode within each end of the envelope and a pair of electrically conductive leads passing through each end of said envelope for coupling each of said electrodes to an energization source, said flourescent lamp characterized by the improvement wherein an electrode disconnect switch is affixed to at least one of said pair of electrical leads associated with at least one of said electrodes within said envelope, said electrode disconnect switch including a bimetal switch normally closed at room temperature and open at a predetermined temperature higher than room temperature and spaced at least one millimeter from said electrode and a pair of electrical conductors coupled to said bimetal switch, one of said pair of electrical conductors of said disconnect switch connected to one of said pair of electrically conductive leads of said lamp and the other of said pair of electrical conductors of said disconnect switch connected to said electrode with the other of said pair of electrically conductive leads of said lamp coupling said electrode to said energization source. 2. The rapid start fluorescent lamp of Claim 1 wherein said electrode disconnect switching is disposed within a glass bottle. 3. The rapid start fluorescent lamp of Claim 1 wherein said electrode disconnect switch is hermetically sealed within a glass bottle. 4. The rapid start fluorescent lamp of Claim 1 wherein said electrode disconnect switch is operable at a temperature in the range of about 750 C to 3000 C. 5. The rapid start fluorescent lamp of Claim 1 wherein said bimetal switch is in the form of a substantially U-shaped bimetal switch. 6. The rapid start fluorescent lamp of Claim 1 wherein said electrode disconnect switch is disposed within a hermetically sealed bottle having a fill gas selected from the group consisting of nitrogen and noble gases. 7. The rapid start fluorescent lamp of Claim 1 wherein said lamp is a 40-watt lamp and said electrode disconnect switch has an average spacing from said electrode of not less than about 8.0 mm. 8. The rapid start fluorescent lamp of Claim 1 wherein said lamp is a 40-watt lamp and said electrode disconnect switch has an average spacing from said electrode -of not less than about 8.0 mm. and not more than about 14.0 mm. 9. The rapid start fluorescent lamp of Claim 1 wherein said lamp is a 40-watt lamp and said electrode disconnect switch is operable at a temperature in the range of about 140 to 1800 C. 10. In a rapid start fluorescent lamp having a glass envelope with a phosphor coated inner wall surface. a fill gas selected from the group consisting of nitrogen and noble gases and a pair of spaced electrodes disposed within the opposite ends of said glass envelope with a pair of electrically conductive leads affixed to each electrode and extending outward of said glass envelope, the improvement comprising at least one electrode disconnect switch disposed with said lamp and having an average spacing of at least one millimeter from one of said electrodes, said electrode disconnect switch having a bimetal switch means normally closed at room temperature and open at a predetermined temperature higher than room temperature with a pair of electrical conductors connected to said bimetal switch means, one of said electrical conductors coupling said bimetal switch to said electrode and the other of said pair of electrical conductors coupling said bimetal switch to one of said electrically conductive leads of said lamp. 11. The improvement of Claim 10 wherein said bimetal switch means is hermetically sealed within a glass bottle and operable.at a temperature in the range of about 750 C to 3000 C. 12. The improvement of Claim 10 wherein said bimetal switch means is hermetically sealed within a glass bottle having a fill gas therein selected from the group consisting of nitrogen, a noble gas and combinations thereof 13. The improvement of Claim 10 wherein said rapid start fluorescent lamp is a 40-watt lamp and said bimetal switch means is hermetically sealed within a glass bottle and operable at an average spacing of about 8.0 to 14.0 mm. from said electrode. 14. The improvement of Claim 10 wherein said rapid start fluorescent lamp i8 a 40-watt lamp and said bimetal switch means is hermetically sealed within a glass bottle and operable at a temperature in the range of about 140 to 1800 C. 15. The improvement of Claim 10 wherein said bimetal switch means is hermetically sealed within a glass bottle having a fill gas selected from the group consisting of nitrogen, noble gases and mixtures thereof.

Inventors: ANDERSON, JOHN W., ROCHE, WILLIAM J.
Applicants: GTE PRODUCTS CORPORATION
Application year: 1984
Main classification: H01J61
IPC codes: H01J61