US 3903447 A
The arc length, light output and efficiency of an elongated discharge lamp, such as a fluorescent lamp, are increased by providing a planar partition within the envelope that extends laterally to the envelope walls and defines a single helical discharge channel that spirals around the envelope axis. The helical partition, electrodes and base contacts are structurally arranged to provide a compact single-ended (or double-ended) lamp of high luminous intensity. Auxiliary electrodes and a starting resistor are included as integral components in one embodiment to provide a self-starting low-pressure discharge lamp of the single-ended variety. In another embodiment the envelope has an axially-extending cavity that is open to the atmosphere and accommodates a rod type laser which is thus tightly coupled optically with the surrounding helical arc and efficiently "pumped" by the lamp. The lamp, in this case, can comprise a "flash" lamp that is pulsed rather than operated continuously.
Claims available in
Description (OCR text may contain errors)
United States Patent Young et al. Sept. 2, 1975  SINGLE-ENDED ELECTRIC DISCHARGE 3,296,480 1/1967 Walz 313/204 LAMP HAVING TUBULAR ENVELOPE 3,504,217 3/l970 Roux et a1. 313/220 X WITH PARTITION MEANS THAT FOREIGN PATENTS OR APPLICATIONS PROVIDES A HEUCAL ARC PATH 906,947 6 1945 France 313 220  Inventors: Robert G. Young, Nutley. NJ; germany ermany Reed Columbus 949,360 9/1956 Germany 313/204  Assignee: Westinghouse Electric Corporation, 273,533 5/l95l Switzerland 313/204 Pittsburgh, Pa. Primary ExaminerPalmer C. Demeo  Flled' 1973 Atzorney, Agent, or Firn1D. S. Buleza  Appl. No.: 337,970
Related U.S. Application Data  ABSTRACT  Division of SCI. No. 191,585, Oct. 22, 1971, which is The 9 length, light Output and efficiency of an 9199- a continuation of $61. No. 696,787, Jan. 10, 1968, gated discharge lamp, Such as a fluorescent p, r abandoned. increased by providing a planar partition within the envelope that extends laterally to the envelope walls  U.S. Cl. 313/493; 313/204; 313/318; and defines a single helical discharge channel that spi- 315/60 rals around the envelope axis. The helical partition,  Int. Cl. 1101,] 17/34; l-lOlJ 61/33 electrodes and base contacts are structurally arranged  Field of Search 313/220, 493, 204, 318; to provide a compact single-ended (or double-ended) 315/59, 60, 99 lamp of high luminous intensity. Auxiliary electrodes and a starting resistor are included as integral compo-  References Cited nents in one embodiment to provide a self-starting UNITED STATES PATENTS low-pressure discharge lamp of the single-ended vari- 1,974,888 9 1934 Barclay 313/204 f efmbodmlent the envelope has 27225439 12/1940 Arens ct aL 313/lO8 X ly-extendmg cavity that 13 open to the atmosphere and 2,314,096 3 1943 Levercnz 313 109 x accommodates a rod type laser which is thus g y 2,501,375 3 1950 Breadner ct 3L 313 109 coupled optically with the surrounding helical arc and 2,847,603 8/1958 Engelbart 313/204 X efficiently pumped by the lamp. The lamp, in this 29 /1 ni et 1 X case, can comprise a flash lamp that is pulsed rather 3,084,271 4/1963 Swanson 313 204 x than Operated continuously 3,121,183 2/1964 Swanson... 313/204 3,262,004 7/1966 Keller 313/220 10 Claims, 10 Drawing Figures i I l2d k 1 16d P I r l4d j i f l f 1 I I I/ZOd 26d j I 15d s I II I I, I, K I,
PATENTEDSEP 2197s SHEET 1 [IF "I: III
PATENTEB SEP 2 ms SINGLE-ENDED ELECTRIC DISCHARGE LAMP HAVING TUBULAR ENVELOPE WITH PARTITION MEANS THAT PROVIDES A HELICAL ARC PATH CROSS-REFERENCE TO RELATED APPLICATION This application is a division of application Ser. No. 191,585 filed Oct. 22, 1971, which application, in turn, is a continuation of application Ser. No. 696,787 filed Jan. 10, 1968, and now abandoned.
BACKGROUND OF THE INVENTION This invention relates to an electric discharge device for generating electromagnetic radiations and has particular reference to an improved single-ended fluorescent lamp.
Despite the fact that fluorescent lamps are more efficient and have longer useful lives than incandescent lamps, fluorescent lighting has not been very successful in replacing incandescent lighting in the home except for certain rooms such as the kitchen and bathroom, etc. Some of the reasons for this lack of interest in the fluorescent lamp as a residential light source are that the lamps are larger, more expensive, require auxiliary equipment and are harder to replace than incandescent lamps. While so-called circline fluorescent lamps are more compact than the standard linear type fluorescent lamps, they are not adaptable to many fixtures and are not too widely used. Simply shortening a conventional tubular fluorescent lamp to make it more compact reduces its efficiency by increasing the relative amount of the energy that is lost at the electrodes. Furthermore, as the lamp voltage drops appreciably below the line voltage a larger voltage drop appears across the series reactor. This increases the power consumed by the reactor and produces a further drop in the overall efficiency of the lighting system. The basic problem involved is to construct a fluorescent lamp which is compact but has a sufficiently long arc length to reduce the electrode losses (relative to the total power input) to a minimum and maintain the lamp current within practical limits.
As a solution to the following basic problem it has been proposed that planar fluorescent lamps be made wherein the arc is bent into a sinuous or spiral configuration by a planar envelope having suitably shaped partitions. Such panel fluorescent lamps are disclosed in US. Pat. Nos. 2,491,847; 3,047,763 and 2,987,640. Improved panel lamps of this type have recently been marketed but they require heavy pressed glassware and are difficult to manufacture.
It has also been proposed that the arc in a standard conventional tubular lamp be made to spiral about the bulb axis in order to increase the arc length. In U.S. Pat. No. 3,121,183 issued to C. E. Swanson this is accomplished by mounting a pair of spaced plates longitudinally within the bulb to partly constrict the discharge and force it to follow a helical path. A similar result is achieved in US. Pat. No. 3,290,538 issued to Larson et a]. without constricting the are by utilizing a glass rod that is of helical Configuration and displaces the discharge toward the opposite side of the bulb so that it follows a spiral path through the bulb. While these designs are successful in that they provide the de sired helical arc, the distance between the adjacent turns of the helix is large so that the actual increase in the arc length compared to the overall lamp length is rather small.
The aforementioned problem of decreasing the physical size of an electric discharge light source without materially shortening the arc length or increasing the power losses is also encountered in the design of light sources for pumping" a laser. This application poses the additional problem of optically coupling the light source with the laser component of material. Heretofore tubular xenon-filled discharge lamps wound in the form of a helix that surround the rod have been used as well as a conventional tubular lamp that is placed at one focal point of an elliptical reflector with the laser located at the other focal point. Coaxial type linear discharge lamps have also been employed in which the arc is confined within an annular chamber defined by two concentric cylinders. The annular chamber extends from one end of the lamp to the other and the laser rod is inserted within the smaller cylinder. A gaseous discharge device of the latter type is disclosed in US. Pat. No. 3,262,004, to C. H. Keller.
SUMMARY OF THE INVENTION It is accordingly the general object of the present invention to provide a fluorescent lamp which will efficiently generate visible radiations by means of an are that is longer yet more compact than those employed in the prior art lamps.
Another and more specific object is the provision of a compact single-ended fluorescent lamp that can be efficiently operated at high power loadings and is adapted for use in residential lighting applications and fixtures.
The foregoing objects and other advantages are achieved in accordance with the present invention by providing a single-ended fluorescent lamp which has a planar partition of helical configuration that spirals around the lamp axis and defines a single helical discharge channel consisting of a plurality of tight turns that are located in side-by-side relation. The aforementioned helical discharge channel is formed by utilizing a cylindrical envelope and a planar helical partition that is attached to an axially extending rod and is so mounted within the envelope that the planar fins or vanes of the helix protrude laterally from the envelope axis to the inner surface of the envelope. One of the lamp electrodes is located at one end of the resulting helical discharge channel and the other electrode is disposed at the opposite end of the channel. Alternatively, both electrodes may be located at the basal end of the lamp and the discharge channel made in such a manner that it spirals through the lamp in one direction and then passes through the lamp in the opposide direction. The helical partition and rod assembly are coated with phosphor and provide an intense area-type" light source when the lamp is energized.
BRIEF DESCRIPTION OF THE DRAWING A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:
FIG. 1 is an elevation view, partly in section, of a compact electric discharge lamp which has a helical arc path and is designed to excite a laser rod that is inserted into a centrally disposed cavity in the lamp;
FIG. 2 is a side ele vational view of the helical partition and support tube assembly utilized in the lamp shown in FIG. 1;
FIG. 3 is an enlarged cross-sectional view through the lamp and laser rod combination along the line III-III of FIG. 1;
FIG. 4 is a side elevational view, partly in section, of another lamp and laser rod embodiment in which the cavity extends completely through the lamp.
FIG. 5 is a similar view of a double-ended fluorescent lamp which is provided with helical arc modifier;
FIG. 6 is an enlarged cross-sectional view through the lamp along the line VI-VI of FIG. 5; and
FIGS. 7 through 10 are side elevational views of various single-ended fluorescent lamp embodiments of the present invention, the envelopes being shown in section to clearly illustrate the internal structure of the lamps.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown an electric discharge device 11 that is specifically designed for use as a pumping source for energizing an elongated body of suitable laser material. The device consists of a cylindrical envelope 12 of suitable vitreous material such as glass or quartz that is hermetically sealed to a hollow vitreous tube 14 that extends along the axis of the envelope and defines a cylindrical cavity 15 that is open to the atmosphere. The free end of the tube 14 is hermetically closed off and the tube is of such length that the laser body, such as a rod R, can be fully inserted into the cavity 15 and thus be positioned coaxially within the envelope 12.
A planar helical partition 16 is fastened to the hollow tube 14 and is arranged so that the planar vanes of the helix extend laterally across the elongated annular chamber defined by the cylindrical envelope 12 and coaxial inner tube 14. The peripheral edges of the helical partition are tightly seated against the inner wall of the envelope l2 and thus provide a single discharge channe] of helical configuration that spirals around the axis of the envelope l2 and the cavity 15 from one end of the lamp 11 to its opposite end. The end of the enve' lope 12 that is spaced from the closed end of the vitreous tube 14 is sealed off and contains an electrode 20 that is supported at one end of the helical discharge channel by a pair of lead wires 22 that are sealed through the envelope wall. A second electrode 24 is similarly supported at the other end of the helical discharge channel by a second pair of lead wires 26 that are sealed through the side wall of the envelope 12 so that the electrode is offset from the envelope axis and spaced from the vitreous tube 14. The electrodes 20 and 24 are of conventional design and consist of tungsten wire coils that have been coated with a suitable electron-emissive material such as the usual mixture of alkaline earth oxides.
The envelope 12 contains an ionizable medium such as a predetermined amount of mercury and a suitable fill gas such as argon, xenon, or neon at a pressure of approximately 10 torr or less.
As is shown in FIG. 2, the vitreous tube 14 and planar helical partition 16 are joined together and form an integral subassembly that is inserted into the cylindrical envelope 12 and anchored therein by sealing the open end of the tube to the end of the envelope. The diameter of the helix is slightly less than the inside diameter of the envelope 12 so that the peripheral edges of the helix seat snugly against the envelope walls. In order to prevent the are from bypassing the helix, it has been found necessary to plug all cracks between the helix and the abutting walls of the envelope. This can be readily accomplished by placing a layer of powdered low-melting glass along the peripheral edge of the helix and then melting the glass frit to form a continuous sealed junction.
The helical partition 16 can be made of curved ribbon glass, ceramic or a suitable sheet metal having a thickness of 0.015 inch or less, the exact dimension being dependent upon the rigidity of the material used. If sheet metal is used, its surfaces must be rendered electrically non-conductive in order to avoid shortcircuiting the discharge. This can be accomplished by covering the metal surfaces with a frit of low melting point glass and then melting the frit to form a smooth insulating layer of fused glass. This construction is utilized in the lamp shown in FIGS. 1 and 3. Hence, as is illustrated in FIG. 3 the planar helical partition 16 comprises a core 27 of sheet metal that is coated with a continuous layer 28 of fused glass.
As a specific example, a lamp of the character shown in FIGS. 1 and 3 was fabricated by utilizing a section of standard lime glass tubing 2% inches in diameter (T17) and 1 1 inches long as the envelope l2 and a sec tion of standard lime glass tubing 1 inch in diameter (T8) and 6 inches long as the inner hollow tube 14. The helix l6 consisted of a ribbon of nickle-iron alloy 0.005 of an inch thick that was centered between the two sections of glass tubing and arranged in the form of a helix having about one turn per inch. The surfaces of the sheet metal helix were coated with glass and the helix was held in place by a layer of fuse solder glass interposed between the edges of the metal ribbon and the respective glass tubes. The length of the are path was approximately 4.7 inches per linear inch of the envelope and the latter was closed with approximately 50 milligrams of mercury and filled with argon at a pressure of 3 torr. The lamp operated at approximately 105 volts for 100 milliamps of alternating current and at about volts for 450 milliamps alternating current. Of course, the optimum fill gas, pressure, current, turns per inch, inner tube diameter, and bulb length and diameter will vary depending upon the specific application. In the case of a lamp designed as a pumping" light source, the various parameters will also be selected so that the electromagnetic radiations generated by the discharge will excite the body of laser material inserted into the coaxial chamber 15 and optimum pumping of the laser will occur.
It should be noted that in the specific example described above, the relative dimensions of the inner tube 14 and envelope 12 and the pitch of the helical partition 16 are such that the cross section of the discharge channel is rectangular and measures approximately 0.5 by 1 inch. In the case of the mercuryvapor argon discharge lamp described the efficiency of the lamp will accordingly be increased since the electron temperature of the plasma will be increased by virtue of the non-circular cross-section of the arc. The losses due to reabsorption and imprisonment of the 2537A resonance radiation will also be reduced because the arc stream will be immediately adjacent the walls of the inner tube 14 and envelope 12. The inserted laser rod R is, accordingly, tightly coupled optically with the discharge.
The outer wall of the envelope 12 may be coated with aluminum (not shown) or otherwise rendered reflective to reflect radiations back toward the envelope axis and thus increase the amount of radiation impinging upon the laser rod. The helical partition 16 and the inner surfaces of the envelope 12 can also be coated with phosphor to alter or supplement the wavelength of the radiations generated by the discharge and thus match the emission spectra of the pumping source with the absorption spectra of the laser material. As a specific example, the laser rod R can comprise a ruby rod or an elongated crystal of neodymium-doped yttrium aluminum garnet.
FIG. 4 EMBODIMENT Another type of an electric discharge device suitable as a pumping source for a laser is shown in FIG. 4. This device 11a is similar to the one described above except that the inner vitreous tube 14a is of the same length as the envelope 12a and is sealed to both ends thereof to provide a coaxial cylindrical cavity 15a which extends completely through the device. The inserted laser rod R is thus coextensive with the pumping source 1 1a and is accessible at both ends. In order to provide clearance for the tube 14a, both of the electrodes a and 2411 are offset from the lamp axis and are held in such position by lead wires 22a and 260 that are sealed through the sides of the envelope 12a.
In this particular embodiment, the outer surface of the envelope 12a is coated with a layer of aluminum to reflect the electromagnetic radiations back toward the axis of the envelope where they pass through the uncoated tube 14 and impinge upon the laser rod R. Of course, the portions of the envelope 12 around the leadin wires 22a and 260 are left uncoated to avoid short-circuiting the electrodes 20:: and 24a.
FIGS. 56 EMBODIMENT In FIG. 5 there is shown a highly loaded fluorescent lamp 1 lb which embodies the helical arc concept of the present invention. The lamp 1112 consists of a cylindrical glass envelope 12b that contains a predetermined amount of mercury, a fill gas such as argon and a planar helical partition 16b that is centrally located and spaced from the thermionic electrodes 20b and 24b sealed into the opposite ends of the envelope. The helical partition 16b is of the same construction as de scribed above in connection with the laser pump embodiments except that the coaxial rigidifying member 14b consists of a glass rod that is considerably smaller in diameter and the surfaces of the rod and partitions are coated with a suitable phosphor P (as shown in FIG. 6) that is responsive to the ultraviolet radiations generated by the discharge. Hence, both surfaces of the planar vanes of the helix are coated with phosphor P while the envelope 12b is left uncoated. Light generated by the phosphor coating on the helix 16b and rod 14b can thus pass directly out of the lamp without having to penetrate a phosphor layer as in the case of a conventional fluorescent lamp. Of course, the inner surface of the envelope 12b can also be coated with a layer of phosphor as in the case of conventional fluorescent lamps.
Calculations have shown that the arc length will be approximately 6 times the linear length of the rod 14b if a helical partition having two turns per inch is used in a lamp having an envelope that is 2 /8 inches in diameter (T17).
The lamp 1 1b is thus quite compact as far as its physical dimensions are concerned but has a surprisingly long arc length. It accordingly operates at a higher voltage per foot of lamp length and at lower current than a standard fluorescent lamp of the same bulb diameter. Lamps embodying the invention are therefore especially adapted for use as highly loaded lamps having input power loadings in the order of 25 to lOO watts per foot of lamp length. Since they inherently have a high impedance and do not require currents of the magnitude required by the highly loaded lamps presently being marketed, the electrode losses are minimized and the design of the cathodes is greatly simplified and their useful life is extended.
Moreover, since the cross section of the discharge channel provided by the planar helix can readily be made non-circular, the electron temperature of the plasma will be increased and the loss caused by reabsorption of 2537A radiation will also be decreased.
FIG. 7 EMBODIMENT The helical arc fluorescent lamps of the present invention can also be made in a variety of single-ended designs, as is illustrated in the embodiments shown in FIGS. 7 to 10. In the embodiment shown in FIG. 7, the lamp consists of a cylindrical glass envelope that is closed at one end by a domed end wall and is hermetically closed at its opposite end by a glass header or stem 15c. The planar helical partition 16: extends along practically the entire length of the envelope 12c and spirals around a coaxially disposed hollow tube 146 that is sealed to the stem 15c and is open at its opposite end. One of the electrodes 20c is located in the space between the tube 14c and envelope wall whereas the other electrode 24c is disposed within the tube 14c. The are thus spirals around the tube from the electrode 20c to the dorned end of the envelope 12c and then follows a straight path through tube 140 to the other electrode 240.
The electrodes 20c and 246 are supported at the end of the envelope 12c by pairs of lead-in conductors 22c and 266 that are sealed through the stem 15c and are electrically connected to pairs of contact pins 34c and 350 that extend from a base member 36c attached to the sealed end of the envelope.
FIG. 8 EMBODIMENT The lamp 11d shown in FIG. 8 is identical with the FIG. 7 embodiment except that the free end of the glass tube 14d is hermetically sealed off and the electrode 24d is located at the domed end of the envelope 12d. It is supported in the aforesaid position by leadin conductors 26d that are sealed through the closed end of the tube 14d, extend through the tube and stem 15d and are connected to the pins 35d carried by the base 36d. Hence, the discharge channel begins at electrode 20d, follows the spiral path defined by the helical partition 16d and terminates at the other electrode 24d located at the opposite end of the envelope 12d.
FIG. 9 EMBODIMENT The single-ended fluorescent lamp lle illustrated in FIG. 9 is of the self-starting type disclosed in U.S. Pat. No. 2,930,934 issued to A. W. Wainio et al. on Mar. 29, 1960. It is constructed in basically the same fashion as the lamp 110' shown in FIG. 8 except that the base 36d is provided with a single pair of contacts 37, 38 and a starting resistor 40 and auxiliary electrodes 42 and 44 are incorporated as integral parts of the lamp structure. One end of the main electrode 200 is connected to the pin contact 37 by a lead wire 39 that is sealed through the glass tube 142 and the stem 156. The other end of the electrode 20c is connected to one end of the auxiliary electrode 42 by a conductor 43 and the opposite end of the auxiliary electrode 42 is connected by a conductor 45 to the starting resistor 40 that is enclosed by and extends along the tube 14c. The opposite end of the starting resistor 40 is connected to one end of the other auxiliary electrode 44 by a lead wire 46 and the other end of the electrode 44 is connected to one end of the main electrode 24e by a conductor 47. The opposite end of the main electrode 24e is connected di rectly to the other pin contact 38 by a conductor 48 that extends through the tube 14c and the stern 15e. The main electrode and auxiliary electrode pairs 200- 42 and 240-44 are thus supported at the opposite ends of the envelope I20 and the ends of the helical discharge channel defined by the planar helix l6e. They are also connected in series with each other and with the resistor 40 and base pins 37, 38.
The auxiliary starting electrodes 42 and 44 are so de signed and the resistance of the starting resistor 40 is such that an electric discharge will be established be tween the auxiliary electrodes when the lamp lle is energized and, immediately thereafter, the main discharge will be established between the heavier operating electrodes 200 and 24a in the manner and in accordance with the teachings of the aforementioned Wainio ct al patent.
FIG. 10 EMBODIMENT In FIG. 10 there is shown still another single-ended lamp 11f consisting of a cylindrical envelope 12]" that is closed at one end by a domed end wall 13f and sealed to a stem 15f in the same manner as the previous embodiments. In this case, however, two intertwined planar helical partitions 16fand l8fare used (the partition 18f is hatched in the drawing to differentiate the partitions and indicate that two are present). The partitions are so arranged relative to the electrodes f and 24f that a single discharge channel is provided which spirals from the electrode 20f located at the basal end of the lamp around the glass tube 14f to the domed end of the lamp between the adjacent faces of the helices, as indicated by the arrows, and then spirals around the tube 14f in the opposite direction back toward the basal end of the lamp between the other set of adjacent faces of the respective helical partitions to the other electrode 24f that is located on the opposite side of the tube 14f. In the illustrated embodiment the discharge channel is one-half the width of those previously described and the helical arc has twice as many total turns. The lower segments 17 and 19 of the helical partitions 16f and ]8f, respectively, are of rectangular form and joined to the tube 14f, stem 15f and the adjacent parts of the wall of the envelope 12f so that the two halves of the envelope are sealed off from one another at the basal end of the lamp. Hence, the electrodes 20f and 24f are accessible to each other only through the intertwined interconnected spiral discharge channels even though they are located at the same end of the lamp 11f.
It will be appreciated from the foregoing that the objects of the invention have been achieved in that various types of compact single-ended fluorescent lamps have been provided which utilize a helical arc path not only to improve the efficiency of the lamps but enable high power loadings to be achieved with lower currents than are required in conventional highly loaded fluorescent lamps.
While several embodiments have been illustrated and described, it will be appreciated that various changes in both the construction and configuration of the lamps and components can be made without departing from the spirit and scope of the invention.
We claim as our invention:
1. A compact single-ended fluorescent lamp adapted for operation at a power input loading of from 25 to watts per foot of lamp length, said lamp comprising the combination of;
a sealed vitreous envelope of tubular configuration and substantially uniform circular cross-section that contains an ionizable medium, coaxially disposed hollow vitreous tube joined to one end of said envelope and extending therefrom toward the opposite end of the envelope, said tube being of substantially uniform circular crosssection and shorter than said envelope so that the free end of the tube is spaced from the proximate end wall of the envelope,
means defining a single helical discharge channel within said envelope comprising an electrically non-conductive planar partition of helical configuration that is integral with and spirals around said hollow tube at a predetermined uniform pitch and extends laterally therefrom to the walls of said envelope,
a pair of spaced electrodes disposed within said envelope at locations such that the arc path begins at one of said electrodes, traverses the single helical channel, and then terminates at the other of said electrodes,
conductor means sealed through said envelope and connectingn the respective electrodes to a plurality of exterior contact elements located on a base member that is secured to said envelope, and
a layer of ultraviolet-responsive phosphor on the surfaces of said helical partition,
the pitch of said helical partition and the diameter of said hollow tube relative to that of said tubular envelope being such that said helical discharge channel is substantially rectangular in cross-section and elongated in a direction parallel to the envelope axis.
2. The compact single-ended fluorescent lamp of claim 1 wherein;
said helical partition has a pitch of from about one to two turns per inch, and
the diameter of said envelope is approximately twice that of the hollow tube.
3. The compact singleended fluorescent lamp of claim 1 wherein the pitch of the helical partition and the diameters of said envelope and hollow tube are so correlated that ratio of the length dimension to the width dimension of the substantially rectangular crosssection of said helical discharge channel is approximately 2:1.
4. The compact single-ended fluorescent lamp of claim 1 wherein;
said helical parition comprises a ribbon of sheet metal that is coated with a layer of insulating material, and
a layer of ultraviolet-responsive phosphor is also disposed on the interior surface of the hollow tube that constitutes part of said helical discharge channel.
5. The compact single-ended fluorescent lamp of claim 4 wherein;
said layer of insulating material comprises a coating of fused glass, and
said envelope is composed of glass and is devoid of phosphor.
6. A compact single-ended fluorescent lamp adapted for operation at a power input loading of from 25 to 100 watts per foot of lamp length, said lamp comprising the combination of;
a vitreous envelope of cylindrical configuration that has a sealed end portion and contains a predetermined amount of mercury and a fill gas at a pressure below torr,
a hollow vitreous tube of cylindrical configuration joined to one end of said envelope and extending therefrom toward the opposite end of the envelope, said tube being coaxially disposed within and shorter than said envelope so that the free end of the tube is spaced from the proximate end wall of the envelope.
means defining a single helical discharge channel within said envelope comprising an electrically non-conductive planar partition of helical configuration that is integral with and spirals around said hollow tube at a predetermined uniform pitch and extends laterally therefrom to the walls of said envelope,
a pair of spaced thermionic electrodes disposed within said envelope at locations such that the arc path begins at one of said electrodes, traverses the single helical channel, and then terminates at the other of said electrodes,
a base assembly that is secured to the sealed end por tion of said envelope and includes a plurality of exposed contact elements, and
a layer of ultravioletresponsive phosphor on the surfaces of said helical partition,
one of said electrodes being located at the sealed end of the envelope in the space between said hollow tube and the proximate side wall of said envelope and connected directly to at least one of said exposed contact elements by a conductor that extends through the sealed end of said envelope,
the other of said electrodes being (a) located at the opposite end of the envelope in the space between the free end of said hollow tube and proximate end wall of the envelope and (b) held in suchposition by a rigid conductor that extends through the hol- 5 low tube and the sealed end of the envelope and is connected to another of said exposed contact elements so that the helical arc path is devoid of conductors and extends from one electrode and spirals around the tube directly to the other electrode at the opposite end of the lamp, and
the pitch of said helical partition and the diameter of said hollow cylindrical tube relative to that of said cylindrical envelope being such that the crosssectional configuration of the helical discharge channel is substantially rectangular and elongated in a direction parallel to the envelope axis.
7. The single-ended fluorescent lamp of claim 6 wherein said base assembly includes two pairs of exposed contact elements and the ends of each of said electrodes are connected to a different pair of said contact elements by a pair of associated conductors.
8. The single-ended fluorescent lamp of claim 6 wherein;
said lamp is of the self-starting type and includes and integral starting resistor, and
said resistor is located within and inclosed by said hollow tube.
9. The self-starting single-ended fluorescent lamp of claim 8 wherein,
said base assembly includes a single pair of exposed contact elements,
one of said electrodes is located adjacent the free end of said hollow tube and connected to an adjacent auxiliary electrode in series therewith,
the other of said electrodes is located at the opposite end of said envelope and connected to a second adjacent auxiliary electrode in series therewith, and
said conductors connect the respective electrodeauxiliary electrode pairs and said starting resistorin series with each other and said pair of exposed contact elements.
10. The self-starting single-ended fluorescent lamp of claim 9., wherein;
the free end of said hollow tube is sealed off,
said resistor extends along and is spaced from the hollow tube, and
a layer of ultra-violet-responsive phosphor is also disposed on the interior surface of said hollow tube that constitutes part of the helical discharge channel.