Description:
BACKGROUND OF THE INVENTION
Fluorescent lamps have in recent years replaced in many instances the conventional filament lamp in view of their many advantages, such as longer life and greater efficiency. Their light output also has been increased materially by the use of improved phosphors and various design features which resulted in a more efficient utilization of the electric discharge. It is a primary object of the invention to provide a fluorescent lamp with greater light output in a given size and with further improved efficiency.
It is another feature of the invention to obtain such increased efficiency by better utilization of the discharge space inside the lamp and by better utilization of the fluorescent coatings. In another aspect of the invention the usefulness of fluorescent lamps is enhanced by their design as a compact unit which includes the operating equipment and allows such compact fluorescent lamps to replace incandescent lamps without resorting to special lamp sockets as are usually employed with fluorescent lamps. Another aspect of the invention is the possibility of its operation with high frequency currents or pulsed direct current of high frequency.
DESCRIPTION OF THE PRIOR ART
In order to obtain compact light sources it is already known to provide within a single or double-ended lamp envelope circuitous paths for the discharge by means of partitions or by appropriately bending the discharge carrying tubes. It is also known to provide discharge tubes with several electrodes at both ends and with substantially parallel arc discharge paths between opposed electrodes to obtain thereby a uniformly illuminated surface. It is furthermore known to operate discharge lamps on multiphase current supply systems.
Fluorescent lamps are also known which have a tube of oval or flat or annular cross section instead of the usual substantially circular cross section in order to obtain improved efficiency or greater current carrying capacity. However, if the flattening, that is the ratio of internal width to internal thickness of a flat tube or of an equivalent annular discharge path is too great, the discharge may not fill the discharge space cross section or may jump from one side to the other instead of constantly filling the whole oval or flat or annular cross section of the tube.
SUMMARY OF THE INVENTION
The present invention relates to a new electric discharge lamp and its associated circuits for operation on single phase alternating current or on direct current circuits. According to the invention, a multiplicity of at least four electrodes is provided at one end of an elongated discharge path which at least to a substantial part is of an annular cross-section. Such electrodes are sequentially energized by connection to mechanical or electronic switching means, preferably of the solid-state type. In a preferred embodiment of the invention the lamp envelope includes an inner tubular envelope spaced by an annular space from an outer lamp envelope and the discharge path will extend through the inner tube and the annular space in series, the electrodes being arranged at the same end of the lamp. In such an arrangement the inner and outer wall of the inner tube and the inner wall of the outer tube may be coated with fluorescent material. In order to obtain a compact arrangement the lamp may be provided with a single base at one end and the auxiliary equipment may be arranged within the lamp base.
DESCRIPTION OF THE FIGURES
FIG. 1 is a preferred embodiment of a fluorescent lamp according to the invention in a longitudinal section,
FIG. 2 is a transverse section taken along the lines 2--2 of FIG. 1 looking in the direction of the arrows,
FIG. 3 is a circuit diagram for operating the lamp of FIG. 1 from a DC supply circuit with pulsed high frequency discharges and illustrates the connections of the electrodes.
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
In FIGS. 1 and 2, 10 is an outer glass envelope of a conventional tubular bulb having a closed upper end 11 and being hermetically sealed at the other end by means of a header 12 provided with an exhaust tube 13 to facilitate evacuation and introduction of the usual filling gas or gases and mercury 14. An inner glass cylinder 15 is concentrically arranged within the outer tubular envelope 10 and sealed to the header 12, being spaced from the outer glass envelope 10 by a discharge space 16 of annular cross section. Thus the header seals both the outer and inner tubular envelopes against the atmosphere at this end. The inner glass cylinder 15 is additionally supported or centered by means of metallic springs 17 at its other or upper end 18, but the inside of the inner tubular envelope 15 communicates at such upper end with the annular space 16 between the two concentric tubular envelopes 10 and 15. Thereby the elongated discharge space inside the inner envelope 15 is serially connected with the annular discharge space 16 between the two envelopes. An activated filamentary electrode 19 such as a coiled coil for direct or alternating current operation or a wire or ribbon for direct current operation is provided at the lower end of the inner glass cylinder 15. A multiplicity of at least four electrodes 20 of a polarity opposite to that of electrode 19 are equally spaced in the space 16 between the inner and outer envelopes around the outer periphery of the lower end of the inner envelope 15. These electrodes may likewise be coiled coils and be coated with an active material as usual in fluorescent lamps. In the arrangement shown eight such electrodes 201, 202, 203...,208 are provided, but more or less may be used and they may be in an even or odd number. They are referred to jointly as electrodes 20. After filling the lamp with an ionizable medium including an inert starting gas at low pressure and a small quantity of mercury 14 and closing the exhaust tube 13, the spacing along the elongated discharge space from the electrode 19 to each of the electrodes 20 forms a low pressure positive column discharge path. The choice of the gas filling is in accordance with standard fluorescent lamp practice. As can best be seen from FIG. 3, one end of each of the electrodes 20 is connected to a metal ring 21, while the other end of each of the electrodes 201, 202, 203 etc. is connected to switching means generally referred to in FIG. 3 by 22. If, in a lamp as just described with fairly large diameter, only one of the electrodes 20 or one extending around the annular cross section were provided, the art would not be diffused through the entire volume between the two envelopes, but would tend to concentrate in a narrow path, thus providing a bright line continuously on one side of the lamp. By providing a multiplicity of electrodes 20 and energizing them sequentially the discharge can move in sequence from one electrode 20 to the next in rapid succession covering the 360° in a few microseconds depending on the operating speed of the switching means 22. Fluorescent coatings 23, 24 and 25 are provided respectively on the inside and outside of the inner envelope 15 and on the inside of the outer envelope 10. As such coatings are known, no further description is deemed necessary.
Upon energization of the lamp a positive column discharge will take place which extends from electrode 19 through the inner tube 15 around its upper edge 18 and through the annular space 16 to one of the electrodes 20 and sequentially to the other electrodes 20. The spacing of the outer and inner tubular envelope should be fairly narrow, for example, 8 to 15 mm.
The arrangement will operate with a high positive column efficiency, as each of the discharges and the resulting generation of 2,537A radiation is rather close to the phosphor coatings 24 and 25 adjacent the annular discharge space 16 and the phosphor coating 23 on the inside of the envelope 15. If additionally the lamp is operated with high frequency a further spreading of the discharge will result in improved utilization of the 2,537A radiation. The number of electrodes 20 employed and their spacing will depend on the diameter and width of the annular space and the spread of the discharge of each electrode 20 and should generally be such that adjacent discharge paths will blend into each other.
As described so far, the lamp of FIG. 1 may be operated with direct current, alternating current, high frequency current or high frequency pulsed direct current and its starting and operating voltage can be given the desired values in accordance with usual practice.
For energizing the electrodes 20 in succession mechanically operable switches, for instance rotating switches, such as synchronous switches on alternating current, or relays or solid state switching devices may be used to shift the power from one of the multitude of electrodes 20 to the next. When solid-state switching devices are employed, it is preferred to integrate all of the components of the driving circuit 22 onto a single substrate which together with the ballasting means may be arranged within the lamp base 26 which, as illustrated, is a screw base with terminal 27 and 28 and comprises a skirt 29 attached to the outer tubular envelope 10. The compact switching arrangement and ballasting or current limiting means may be housed within the skirt 29 of the base 26 and this is represented schematically by 30 which includes the ring 21 and switching means 22.
While the electrode 19 has been illustrated as being arranged at the lower end of the inner tubular envelope 15, it could also be arranged at the outer upper end thereof, i.e. in the annular space 16, in which case the upper end of the tube 15 may be sealed directly to the upper end of the outer tubular envelope 10 and an exhaust tubulation connected directly to the annular discharge space 16. In such modification, the lead wire for electrode 19 may be sealed through the upper end of the annular discharge space 16 and the discharge would then take place only in the annular outer space 16. In such case the inner tubular envelope 15 may be left open to the atmosphere at both ends, and, if desired, the lead-in wire for the electrode 19 may be run through the inner tube 15 and connected to the equipment 30 in the base 26 at the lower end of the lamp, or it may be connected directly to a corresponding contact at the upper end.
While one end of the electrodes 20 is connected to a common ring member 21, the other ends of the electrodes 20 are connected to the switching means 22 arranged in such a way that power is applied sequentially to one of the electrodes 20 at a time and shifted from such electrode to another in rapid succession.
DESCRIPTION OF A PREFERRED OPERATING CIRCUIT
FIG. 3 illustrates a driving circuit for the sequential arc lamp which uses a ring counter for high frequency operation of the type illustrated in General Electric Transistor Manual, Seventh Edition, p. 431. The ring counter illustrated supplies high frequency pulsed direct current to the sequential arc lamp of FIG. 1. The electrode 19 is connected through a suitable impedence 31 to the positive side 28 of a direct current line or the output of a rectifier bridge energized from an AC source and operates then as an anode. The ring counter of FIG. 3 has a positive line or ring 32 connected to the positive side 28 of the direct current source, a negative ring or line 33 connected to the negative side 27 of the current source and a trigger ring or line 34. Since in the lamp illustrated in FIGS. 1, 2 and 3 eight electrodes 201 , 202 , 203 ...20 8 are provided the ring counter has correspondingly also eight silicon controlled switches 351 , 352 , 353 ...35 8 which have their cathode end connected to the negative ring 33 and their other or anode end connected to the free end of a corresponding one of the electrodes 20. Thus the anode end of 351 is connected to electrode 201 , the anode end of 352 to electrode 202 etc. Each of the silicon controlled switches 35 has an anode gate 36 and a cathode gate 37. The anode gate 36 of each of the silicon controlled switches 35 is connected to the positive ring 32, each through its own high resistor 38. The cathode gate 37 of each of the silicon controlled switches 35 is connected to the junction 39 of a coupling capacitor 40 and a diode 41. The coupling capacitor 40 charged during operation of silicon controlled switch 351 is numbered 401 , the one charged during operation of silicon controlled switch 352 is numbered 402 and so on. The second or cathode end of the diode 41 is connected to the triggering line or ring 34, while the other end of the capacitor 40 is connected through a low charging resistor 42 to the anode side of its silicon-controlled switch 35. For instance, capacitor 401 is connected to the anode side of silicon controlled switch 351 on the one hand and to the cathode gate of silicon controlled switch 352 on the other hand. Connected between the anode gate of one of the silicon controlled switches 35, such as 351 , and the negative ring 33 is a grounding switch 43 which may be a push button switch or other manually operated switch, but preferably is automatically actuated, when the power is applied to the circuit terminals 27 and 28. The grounding switch 43 is only momentarily closed to start the operation of the ring counter, or it is normally closed and is opened when the lamp circuit is energized. As illustrated, the switch is a magnetic switch, but a thermal switch or solid state relay may be used.
Shift pulses of 5 to 10 microseconds duration are applied to the trigger line or ring 34 of the ring counter through a transistor 44 from a suitable pulse generator 45 which is energized from the current supply line 27/28. The pulse generator illustrated comprises a unijunction transistor 46 the base ends of which are connected through two resistors 47 and 48 to the current supply line 27, 28. The emitter of the unijunction transistor 46 is connected to the junction of a capacitor 49 and a resistor 50 which are connected in series to the current supply line 27, 28. The capacitor 49 is charged through resistor 50 until the emitter voltage E reaches a voltage at which the unijunction transistor 46 turns on and discharges the capacitor 49 through resistor 47. When the emitter voltage reaches a certain minimum value, the emitter ceases to conduct, transistor 46 turns off and the cycle is repeated, thus applying pulses to the transistor 44 to perform the shifting operation.
Assuming the grounding switch 43 were open when power is applied to the terminal 27, 28, none of the eight silicon-controlled switches (stages) 35 will turn on until the anode gate of one of the silicon-controlled switches 35, for instance 351 , is grounded. This is accomplished by the momentary closing of the switch 43 which remains then open as long as the power is applied to the circuit. When the silicon-controlled switch 351 has become conductive by grounding of its anode gate 36, the full line voltage of the direct current power supply 27, 28 appears between the associated electrode 201 and the common electrode 19 of the lamp. The line voltage, for instance 120 volts, is sufficient to cause ionization of the starting gas in the correspondingly designed lamp and produces an arc discharge between the electrodes 19 and 201 . The next pulse from the pulsing network 44, 45 puts a reverse bias on the trigger line 34 of the ring counter, reverses the bias of the cathode gate 37 of silicon-controlled switch 351 and turns off the switch 351 . In the meantime, i.e. during current flow through the silicon-controlled switch 351 , the coupling condenser 401 connected to the cathode gate 37 of silicon-controlled switch 352 has been charged and the charge stored on that condenser 401 then triggers the next stage 352 into operation, so that the arc is transferred from electrode 201 to 202 . While the discharge takes place between electrode 202 and electrode 19 acting as an anode, the coupling condenser 402 connected to the cathode gate 37 of silicon-controlled switch 353 is charged so that the next shift pulse will turn off the conducting silicon-controlled switch 352 by putting a reverse bias on its cathode gate 37 and allow the charge stored on the coupling condenser 402 to trigger the next stage 353 . In similar way all silicon-controlled rectifiers 35 are sequentially operated and the electrodes 20 sequentially energized. The repetition rate of the shift pulses, which in the arrangement shown may be of the order of 20 kilohertz, will determine the frequency with which the arc will travel around the 360° path provided by the lamp envelope configuration of FIG. 1. Control of the arcs in the fluorescent lamp is obtained by the impedance 31 in series with the common electrode (anode) 19 or by other current limiting means. The impedance 31 may take the form of a suitable resistance element for pulsed DC operation or may be a capacitive or inductive reactance for alternating current operation.
While the illustrated operating circuit and its mode of operation appear somewhat complex, the physical size and cost of the components are relatively small and will not adversely affect the benefits obtained by the lamp illustrated in FIG. 1. It is now practical and economical to integrate all or substantially all of the components of the driving circuit onto a single substrate and the complete switching and pulsing arrangement illustrated in the example of FIG. 3 can be provided on a disc approximately 3- 4 cm, in diameter and half a centimeter thickness.
The invention is not limited to the exact construction shown or to the particular ring counter illustrated in FIG. 3, as various modifications of the construction will readily appear to persons skilled in the art and many other sequential switching means can be used without departing from the gist of the invention or the scope of the attached claims.