Background of the Invention The research in the field of discharge lamps has been carried out for over 70 years, and fluorescent and other gas discharge lamps have been a commercial reality for about 60 years. By now, various methods for starting and operating gas discharge lamps have been studied and put into operation. The most widely used known methods and circuits are circuits comprising a ballast and a starter, circuits comprising an electronic ballast, or circuits comprising ballast and transformer (the so-called "rapid-start") systems.

In circuits with a starter having a bimetallic plate, there is no fixed time for pre-heating of electrodes. If the plate is of inferior quality, the lamp flickers and starting is complicated. Furthermore, starters with bimetallic plate are of much lower quality than electronic starters. If an electronic starter is used, the pre-heating time is fixed and sufficient for ensuring favorable starting conditions. In circuits with electronic ballasts without pre-heating, the starting cost increases considerably; the electrodes wear out, the tube ends darken, and the lamp is soon out of service. In circuits with electronic ballast and pre-heating of electrodes, favorable starting conditions are usually achieved, whereas with starter systems without pre-heating, such systems usually do not comply with the requirements of IEC International Standards.

During starting of a fluorescent lamp, a spot which is an intensive source of electrons appears on the electrode instantaneously serving as a cathode. The spot always appears on the spiral end of the electrode to which the voltage is supplied.

With each starting action of the lamp, the spot moves farther away from the electrode's spiral end, and during operation it moves along the electrode's spiral from its end towards the unburned part of the oxide coating.

In the anode, during the same half-cycle, the current distribution along the length of the spiral is not symmetrical. Therefore, the part of the electrode's spiral which is closer to the end to which power is applied becomes overheated, while the opposite part is heated insignificantly. As a result, since the electrodes in different half-cycles serve alternatively as cathode and anode, the cathode spot, in its movement along the spiral, reaches approximately its middle. This is caused mainly because during the movement of the spot, voltage drop on the electrode's spiral itself reaches a certain level, and about half of the spiral is not sufficiently heated. In such starting circuits, about half of the oxide layer on the electrode spirals is burned out, the exposed part of the spiral is overheated, and in turn, it burns out. In case of a homogenous spiral, it usually burns out in the cathode half-cycle approximately in the middle section thereof, and in the anode half-cycle, it burns out near the end portion to which the voltage is supplied. Hence, the fluorescent lamp does not utilize its full potential, and its active life is shortened.

In rapid-start systems, the electrode spiral is constantly heated. This is achieved by introducing a transformer into the circuit. The electrodes are connected to the transformer's windings which supply heating current to the electrodes.

The lamp is started in the following stages: First, the lamp is switched on, the electrodes are heated, and the voltage is supplied through the ballast. The voltage formed with the participation of the ballast does not exceed 400 V. The lamp can be started only when thermoelectronic emission is sufficiently intensive. In the existing circuits, this process takes about 1 second. Thus, the electrodes are in unfavorable conditions from the moment they are switched on until the lamp is started. The glow discharge phase, which is required to achieve sufficient electronic emission, has a negative effect on the electrodes and leads to their fast wear. This phenomenon does not have an explosive character, as it does in instant-start circuits where the lamp is started by applying high voltage to the electrodes without pre-heating, but it still negatively affects the lamp's life.

In steady-state operation, the opposite takes place: the electrode spiral is overheated, especially in the anode half-cycle. This is because, besides the constant heating of the spiral by the transformer, there is an additional heating by the lamp's current. In cathode half-cycle there is less overheating, due to the cathode cooling by electrons emitted from its surface.

It can thus be understood that the prior art rapid start systems do not provide the most favorable conditions for the lamp's electrodes, however, the lamp's life in this case does not decrease, but rather it increases, compared to the other types of circuits discussed above. This is due to the fact that in such rapid start systems, the entire oxide layer on the electrode spirals is used up during the lamp operation period, and not about one-half of it, as is the case in the other starting circuits discussed above.

In evaluating rapid-start systems as a whole, their most serious drawback is that they contain transformers, which consume electrical power, release heat, increase the overall weight of the system, and make assembly of the light fixture more complicated.

Summary of the Invention The above-mentioned disadvantages of starters for fluorescent lamps are eliminated by a new operational algorithm or series of stages, which is a subject of the present invention, based on a new principle of starting and operating a discharge lamp, the details of which stages are as follows: 1. The first stage requires pre-heating of electrodes for achieving a sufficiently high thermoelectric emission before supplying the voltage for switching on the lamp, i.e., for ensuring a smooth start. The heating time is set by the starter circuit, on the basis of research for each particular type of lamp. The starting time is optimized, to make the starting maximally pleasant to the user's eye.

2. In the second stage after the pre-heating stage, the electrode's ends are shorted.

3. In the third stage, voltage is applied to the electrodes to start the lamp, and a spot appears on the lamp's cathode. As discussed hereinbefore, the cathode spot is also characteristic of this system, however, the electrodes of the present invention are in more favorable conditions, and the cathode spot is less pronounced. This is so since the electrodes serve as cathode and anode alternatively. Measurements of the cathode energy balance show that the largest fraction of energy which heats the cathode comes from the electron collisions in the anode half-cycle. In the circuit of the present invention, the temperature field of the electrode in the anode half-cycle is symmetrical with respect to the axis passing through the spiral middle and normal to it. As a result, the thermoelectric emission in the cathode half-cycle which is needed to ensure normal lamp operation is provided not only by the emission from the cathode spot, but also from the other heated part of the spiral.

The above phenomenon considerably reduces the intensity of the cathode spot; this can be observed visually in some lamps. The burning of the spiral is thus prevented, evaporation of the cathode material decreases, and therefore, a sufficiently low starting cost is ensured.

The main advantage of the circuit of the present invention, however, is the possibility for the cathode spot to emerge at both spiral ends, because after the electrodes have been pre-heated and the spirals shorted, the two spiral ends are in the same physical state. It means that the formation of the cathode spot during the first starting cycle is equally probable at both ends. In subsequent startings, the location of the cathode spot depends on the degree of burning out of the oxide coating on the spiral ends, on the value of voltage drop on the spiral beginning from its end, and on the temperature of the spiral ends.

Hence, during the ignition period, the cathode spot may appear on one or the other end of the electrode spirals, depending on the above-mentioned factors, and during lamp operation, the cathode spots can be seen as moving from both ends towards the center of the spiral until the oxide coating is completely burned out. The lamp potential is thus fully used, without such negative side effects.

It is therefore a broad object of the present invention to overcome the above- mentioned disadvantages of the prior art starter systems and to provide a method for igniting fluorescent and other gas- or vapor-discharge lamps in which a more even burning out of the oxide coating of the electrodes is achieved.

It is a further object of the present invention to provide a starter and control unit for gas- or vapor-discharge lamps which is reliable, easy to manufacture, and which exhibits energy and cost savings, both by significantly extending lamp life and by requiring very low power consumption during use.

The invention achieves the above objectives by providing a method for igniting a discharge lamp of the type connectable across the mains via a ballast, comprising applying to the lamp's electrode spirals pre-heating voltage for a predetermined period of time, short-circuiting the electrode spirals, and applying the mains voltage across the electrodes.

The invention further provides a starter and control unit for a gas discharge lamp, having electrode spirals connectable across a mains of an AC power source and operating in conjunction with a standard ballast, said unit comprising a starter unit having circuit means for regulating the starting of the gas discharge lamp in a controlled and timed sequence, said sequence including a pre-heating stage wherein the electrodes of the lamp are heated for a predetermined period of time, an igniting stage wherein said electrode spirals are short-circuited, and a steady-state operation stage in which said electrode spirals remain short-circuited.

Brief Description of the Drawings The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood.

With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

In the drawings: Fig. 1 is a schematic illustration of a starter and control unit according to the present invention and the manner of interconnecting same; Fig. 2 is a detailed circuit diagram showing an embodiment of a starter and control circuit of a gas discharge lamp according to the present invention for operating a gas discharge lamp with an electromagnetic ballast, and Fig. 3 is a circuit diagram showing a further embodiment of the invention.

Detailed Description of Preferred Embodiments Fig. 1 schematically illustrates the starter and control unit 1 according to the present invention, and the manner in which it is connected, via a ballast 2, to a fluorescent discharge lamp 4 having electrodes 6 and 8.

Referring now to Fig. 2, there is shown a detailed circuit diagram of the starter and control unit 1 according to the present invention as connected in a discharge lamp circuit, and a ballast. As seen, electrodes 6 and 8 are bridged by a normally closed switch 10. A protective capacitor 12 is advantageously connected in parallel across the switch 10.

Across the mains terminals P, N are connected a capacitor 14 and rectifier bridge 16, and the output of bridge 16 is connected to electrolytic capacitors 18, 20 and variable resistor 22. A relay 24 operating the switch 10 is also connected to the bridge 16. A relay 26, controlling normally open switches 28, 30 and 32, is connected between the resistor 22, the capacitors 18 and 20, and in turn to the bridge 16. The pattern A of current distribution in the anode half-cycle is depicted adjacent to the lamp electrode 8. As can be seen, the current distribution is evenly distributed about the electrode's entire ends.

When voltage is applied to input terminals F, N, i.e., when the lamp is turned on, current is divided between several circuits. A first circuit provides pre-heating of the electrodes 6 and 8 in order to achieve a required level of thermoelectric emission.

The heating time is set by the RC circuit, consisting of variable resistor 22 and capacitor 20. The second circuit, the control circuit, consists of two relays 24 and 26, which are turned on by connecting the low voltage DC power supply provided by rectifying bridge 16 and capacitors 14 and 18 which reduce and rectify the input voltage.

When voltage is applied to relay 26, the relay's switches 28, 30 and 32 react simultaneously, closing the sections of the circuit to which they are connected, thereby shorting the electrodes 6 and 8; upon closing of switch 28, relay 24 is energized and, in turn, opens switch 10. At this moment, due to the self-induction of ballast 2, an increased voltage is applied to the lamp electrodes 6 and 8 and the lamp is ignited. Current begins to flow in the lamp's circuit and the lamp provides steady illumination.

When the lamp is turned off, there is no voltage at the input terminals, and relays 24 and 26 are turned off. The switches thus return to their normal state shown in Fig. 1, and when the lamp is turned on again, the cycle is repeated.

Fig. 3 shows the starter unit 1 according to the present invention, as utilized with, e.g., an electronic ballast using an IR2155 driver. The per se known electronic ballast and driver 34 is connected in a circuit between the starter unit 1 and the lamp's electrodes 6 and 8. The operation of this embodiment is similar to the operation as described hereinbefore with reference to Fig. 2.

It should be noted that instead of the switching relays shown in Fig. 2, other types of switching devices, such as solid state switches or switching circuits, could be utilized.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.