WO2006006844A2

WO2006006844A2 - Gas discharge lamp with stabilisation coil

Info

Publication number: WO2006006844A2
Application number: PCT/NL2005/000460
Authority: WO
Inventors: Paul Henri Frank De Haan; Peter Hans Wassink
Original assignee: Crossworks Contra Consulting Bv
Current assignee: Crossworks Contra Consulting Bv
Priority date: 2004-07-09
Filing date: 2005-06-29
Publication date: 2006-01-19
Anticipated expiration: 2007-01-09
Also published as: NL1026622C2; WO2006006844A3

Abstract

Disclosed is a gas discharge lamp comprising a gas discharge body (2) and magnetic means at least partially disposed near the gas discharge body for influencing the gas discharge at the interface formed at the surface of the electrode(s). The magnetic means are provided with at least one stabilising coil (3-1, 3-2, 3-3) for stabilising the gas discharge in use, both in the gas discharge body and at the electrodes of the lamp. The same coil that functions as a stability-enhancing coil in the case of a stationary gas discharge functions in a multifunctional manner as a starter coil prior thereto for the purpose of facilitating the initiation of the gas discharge. An increased concentration of the gas discharge leads to an improved light output of the gas discharge lamp.

Description

GAS DISCHARGE LAMP WITH STABILISATION COIL

The present invention relates to a gas discharge lamp comprising a gas discharge body in which electrodes are disposed for generating a gas discharge in said gas discharge body, and magnetic means disposed near the gas discharge body for influencing the gas discharge.

Such a gas discharge lamp is known from US-4, 982, 140. The gas discharge lamp that is known therefrom comprises a gas discharge body in which a gas or plasma discharge is initiated - whether or not by means of electrodes - for the high-intensity gas discharge lamp that is to be used as a light source. Magnetic means in the form of coils are arranged in and around the gas discharge lamp. Inside the gas discharge body, movable coils are disposed on one side of the gas discharge, which coils are wound in opposite directions and which function to assist in initiating a the gas discharge. Disposed outside the gas discharge body is an excitation coil fed by a radio-frequency power source, which functions to maintain the gas discharge in the gas discharge body in use.

A drawback of the known gas discharge lamp is the complex, internally movable construction and the high degree of colour change that the vertical gas discharge exhibits.

It is an object of the present invention to provide an improved gas discharge lamp, which is of simpler construction and in which the gas discharge exhibits a lower degree of colour change.

In addition to that it is an object of the present invention to realise a higher light output and to make it possible to control the amount of light that is produced.

In order to accomplish that object, the gas discharge lamp according to the invention is characterized in that said magnetic means are arranged at least round the electrode (s) for influencing the interface of the gas discharge formed at the electrode (s) .

The present invention is based on the perception that the gas discharge characteristics that are important in order to obtain a properly functioning gas discharge lamp, such as the maximum light output, the stability, the colour composition and the possibility to control the generated light, are to an important extent determined by the behaviour of the plasma discharge at the so called interface or boundary plasma layer, i.e. around the electrodes . The interface appears to be an impeding factor as regards a satisfactory development of a stable and, if desired, large and controllable plasma main flow in the interior of the lamp. By concentrating the magnetic field generated by the magnetic means on the electrodes, said impediment is counteracted, with the plasma in the interface being blown away magnetically from the electrode in question, thus enabling an increased particle main flux. The efficiency of the gas discharge lamp according to the invention in terms of light output appears to increase considerably as a result of this.

One embodiment of the gas discharge lamp according to the invention is characterized in that the magnetic means are arranged for forming a controllable magnetic field in the interface for increasing or decreasing the plasma.

With this embodiment of the invention it has become possible to increase or decrease the plasma accumulation in the interface around the electrode (s) , enabling the gas discharge as a whole to produce a dimmable amount of light.

Another embodiment of the gas discharge lamp according to the invention is characterized in that the magnetic means are provided with one or more stabilising coils to be coupled to the gas discharge in the gas discharge body for stabilising the gas discharge in use.

The gas discharge lamp according to the invention has this advantage that said at least one stabilising coil is disposed and fed either inside or outside the gas discharge body, and that the magnetic field thus generated near the location of the gas discharge has a stabilising effect on the gas discharge. The same at least one coil that functions as a stability-enhancing coil in the case of a stationary gas discharge functions as a starter coil prior thereto, in a multifunctional manner if desired, for the purpose of facilitating the cold or hot initiation of the gas discharge. The construction of the gas discharge lamp has thus been simplified, whilst the functionality has been improved.

The multifunctional starting/stabilising coil reduces the occurrence of convection in that the magnetic field generated by the gas discharge forces the gas discharge towards the centre of the aforesaid coil of the gas discharge lamp. As a result of the concentration in the centre of the lamp that is thus achieved, the plasma discharge as a whole will have a grater intensity. The plasma process proceeds more efficiently and more light is produced by the lamp. It has furthermore become apparent that the influence of a separation of the components in the gas discharge body, which results in a colour change, is more effectively counteracted. The extent of the colour change along the more centrally located and more locally occurring gas discharge decreases, therefore. Since the gas discharge is more concentrated, the light output increases.

Another embodiment of the gas discharge lamp according to the invention is characterized in that said at least one stabilising coil and said gas discharge body are connected in series.

The same current that maintains the gas discharge also passes through the multifunctional coil in that case. No external power source for the coil or coils is needed in that case, which reduces the cost price.

Yet another embodiment of the gas discharge lamp according to the invention, by means of which it becomes possible to control the gas discharge, is characterized in that the gas discharge lamp comprises a power supply circuit connected to said at least one stabilising coil for providing a stabilising current.

Yet another embodiment of the gas discharge lamp according to the invention is characterized in that the number of windings per unit length of said at least one stabilising coil is variable. This makes it possible to optimise the local magnetic field strength.

Another embodiment of the gas discharge lamp according to the invention is characterized in that said at least one stabilising coil comprises at least two coils, which may be wound in opposite directions, as a result of which the gas discharge can be effectively retained therebetween by the coil or coil portions exerting opposing forces . The gas discharge lamp according to the present invention will now be explained in more detail with reference to the figures below, in which like parts are indicated by the same numerals. In the figures: Figure 1 shows a first embodiment of a gas discharge lamp according to the invention, comprising a stabilising coil;

Figure 2 shows a second embodiment of the interior of a gas discharge lamp according to the invention, comprising a stabilising coil portions having a different number of windings per length;

Figure 3 shows a third embodiment of the interior of a gas discharge lamp according to the invention, comprising two stabilising coils; Figure 4 shows a fourth embodiment of a gas discharge lamp according to the invention, comprising groups of stabilising coils; and

Figure 5 shows a fifth embodiment of the interior of a gas discharge lamp according to the invention, comprising stabilising coils disposed outside the gas discharge body.

Figure 1 schematically shows the construction of a gas discharge lamp 1 which, apart from the usual constructional components, comprises a gas discharge body 2 and magnetic means, in this case in the form of a stabilising coil 3, arranged around the gas discharge body 2. The gas discharge body 2 and the magnetic means 3 are placed in a transparent casing 4, which is usually made of glass. In this embodiment, the body 2 comprises two electrodes 5-1 and 5-2 (see figure 3) , which are electrically fed. In this case the stabilising coil 3 extends practically the entire length of the gas discharge body 2, which, upon being electrically fed, generates a magnetic field surrounding at least one gas discharge G (see fig. 5) , which is initiated in the body 2 in a known manner. The field strength, i.e. the number of ampere- windings per metre (the pitch of the windings) is such that in this embodiment the plasma arc or gas discharge is forced towards the centre of the coil 3 when stationary, concentrating on the central axis thereof, which leads to an increased conversion efficiency and an increased light output.

In the embodiment that is shown in figure 1, the coil 3 forms part of the magnetic means 3 that blow the plasma away from at least one of the electrodes 5-1, 5-2 at the plasma interface formed around said electrode (s) . In the gas discharge body 2 itself, the magnetic field of the coil 3 stabilises the plasma that is formed therein, as a result of which the extent of colour mixture and the aforesaid colour change is reduced.

During cold or hot (re) starting of the lamp 1, a separate supply voltage connected to the coil 3 might provide the desired starting field in that case, stimulating the formation of the gas arc, so that a stabilising current through the coil 3 might result in the stabilisation of the gas discharge after some time.

As shown in figure 1, the body 2 and the coil 3 may be connected in series, in which case a separate supply source is not needed. Furthermore, automatic composition takes place in that case, i.e. as the gas discharge flow increases, also the stabilising current through the coil 3 will increase, as a result of which the field that is thus stabilised in stationary condition is compressed or pinched more strongly. The magnetic compression of the plasma being formed in this manner causes the light yield of the lamp 1 to increase.

The stabilisation coil 3 that is present in the (schematically shown) interior of the lamp 1 of figure 2 is built up of several coil portions indicated 3-1, 3-2 and 3- 3, which are connected in series in this case. In this embodiment, the portions 3-1 and 3-3, which may be wound in the same direction, possibly with variable winding pitch, and their magnetic fields retain the pulsating plasma arc on the left and on the right, whilst the magnetic field of the central coil 3-2 compresses the plasma in the direction of the central axis of the coil 3. The coil portions may have different diameters, if desired, and/or a different number of ampere-windings per metre.

Figure 3 schematically shows the interior of a gas discharge lamp 1 comprising two coils, e.g. wound in opposite directions, which are disposed on either side of and outside the plasma arc of the gas discharge body 2. In the case of a gas discharge from the left to the right, the left-hand coil 3-1 acts in the same direction as the discharge during the first phase of a period of the alternating supply voltage, whereas precisely the reverse takes place during the next period. As a result, the plasma will also move/vibrate slightly when an alternating supply voltage is used, and this pulsating effect causes the components in their gas discharge body 2 to be mixed, as a result of which separation and the accompanying colour change of the gas discharge is prevented.

In the embodiment of figure 3, the plasma in the interface present at the surface around each one of the electrodes 5-1 and 5-2 is also forced towards the centre of the body 2 as a result of the opposed winding directions of the coils 3-1 and 3-2, in particular if the magnetic means are present around the electrodes, which likewise causes the aforesaid light yield to increase. Figure 4 shows an embodiment comprising two groups of coils Sl and S2, each comprising four stabilising coils in this case, which generate a magnetic field which is directed towards the central axis of the plasma body 2 for at least part of a period. Generally, at least two groups of at least two to maximally eight stabilising coils will be used. One supply unit (not shown) may be provided for each coil or group of coils so as to effect the desired , possibly moving, magnetic field configuration. Such circuits may be integrated in a lamp base or socket, if desired.

Figure 5 shows another embodiment of the gas discharge lamp 1, in which two stabilising coils 3-1 and 3-

2 are disposed entirely outside the gas discharge body. In the coils 3-1 and 3-2, magnetic field-conducting core materials are used, which terminate at an oblique angle with respect to the central axis H at the ends of the gas discharge body 2 so as to retain the plasma laterally as well as concentrate it around the central axis H. This principle can also be used advantageously with existing gas lamps .

When the magnetic field generated by the stabilising coil or coils is larger, e.g. more than ten times larger, than the local geomagnetic field, the latter will have less influence on the forming and maintaining of the gas discharge. Furthermore, the field of the stabilising coil 3 has a diminishing effect on the known bending of the gas discharge to a corkscrew shape, with the plasma being pulled straight, as it were. If a high Q-value of the coil

3 leads to undesirable resonant rise, a resistor to be connected in parallel therewith can provide attenuation.

The lamp 1 might comprise a secondary electrode for improving the starting behaviour, or be of an electrodeless type. By switching coils, e.g. switching on or switching over, it becomes possible to influence the direction of one or more local magnetic fields, among other things, in dependence on the temperature, e.g. by means of a bimetal switch. According to one possibility, the gas discharge lamp is started, whether or not by means of starter coils, and the stabilising coils 3 are switched on once a desired operating temperature has been reached, so as to retain the plasma in question in the manner that is desirable at that point .

The stabilising coil or coils 3, 3-1, 3-2, 3-3, Sl, S2 may comprise one or more layers of windings. Furthermore it is possible for several coils, e.g. having a mutually different winding pitches and/or wire diameters, to be wound over each other. One or more of the aforesaid coils may be connected to a frequency and/or phase controlled circuit, so that a signal is delivered to the coils whose strength, frequency and phase are such that, given the coil configuration in question, an optimally stabilised and steady (to the human eye) discharge and light image is obtained.

From the foregoing it will furthermore be apparent that in those cases in which mention is made of stabilising coils 3, said coils should not only be considered as magnetic means in the form of coils that stabilise the plasma inside the body 2 and at the electrodes, but that they can also be considered as magnetic means that may function, possibly simultaneously, as means for pushing against the plasma interface that impedes the particle flux away from the electrodes. When the plasma is pushed away from the two electrodes 5-1 and 5-2, a spherical plasma discharge as shown in figure 5 is formed, whereas an hourglass-shaped discharge (not shown) is obtained when the plasma is pushed (or pulled) towards the electrodes.

Said pushing away or attracting or, put more generally, influencing has been explained in the foregoing as being based on magnetic influencing, but it is understood to include also a physically equivalent manner of electric or electromagnetic influencing.

Claims

1. A gas discharge lamp, comprising:

- a gas discharge body in which electrodes are disposed for generating a gas discharge in said gas discharge body, and

-magnetic means disposed near the gas discharge body for influencing the gas discharge, characterized in that said magnetic means are arranged at least round the electrode (s) for influencing the interface of the gas discharge formed at the electrode (s) .

2. A gas discharge lamp according to claim 1, characterized in that the magnetic means are arranged for forming a controllable magnetic field in the interface for increasing or decreasing the plasma.

3. A gas discharge lamp according to claim 1 or 2, characterized in that the magnetic means are provided with one or more stabilising coils to be coupled to the gas discharge in the gas discharge body for stabilising the gas discharge in operation.

4. A gas discharge lamp according to claim 3, characterized in that said at least one stabilising coil and said gas discharge body are connected in series.

5. A gas discharge lamp according to claim 3 or 4, characterized in that the gas discharge lamp comprises a power supply circuit connected to said at least one stabilising coil for providing a stabilising current.

6. A gas discharge lamp according to any one of the claims 3-5, characterized in that the number of windings per unit length of said at least one stabilising coil is variable.

7. A gas discharge lamp according to any one of the claims 3-6, characterized in that said at least one stabilising coil comprises at least two coils.

8. A gas discharge lamp according to claim 7, characterized in that said at least two coils are or may be wound in different directions.

9. A gas discharge lamp according to any one of the claims 3-8, characterized in that the gas discharge body is disposed in the magnetic field within said at least one stabilising coil.

10. A gas discharge lamp according to any one of the claims 3-9, characterized in that said at least one stabilising coil is fed with supply current in such a manner that the generated magnetic field is larger than the geomagnetic field.

11. A gas discharge lamp according to any one of the claims 3-10, characterized in that several stabilising coils are arranged in groups around the gas discharge body.

12. A gas discharge lamp according to claim 11, characterized in that said groups of stabilising coils are disposed on either side of the gas discharge body.

13. A gas discharge lamp according to any one of the claims 3-12, characterized in that the stabilising coil (s) is (are) provided with a yoke that conducts magnetic field lines.

14. A gas discharge lamp according to any one of the claims 3-13, characterized in that the magnetic field generated by the stabilising coil (s) is oriented mainly toward the gas discharge.

15. A gas discharge lamp according to any one of the claims 3-14, characterized in that the gas discharge lamp comprises several supply circuits for said at least one stabilising coil .

16. A gas discharge lamp according to any one of the claims 3-15, characterized in that at least one supply circuit is integrated in the gas discharge lamp.

17. A gas discharge lamp according to any one of the claims 3-16, characterized in that the gas discharge takes place substantially horizontally.

18. A gas discharge lamp according to any one of the claims 3-17, characterized in that the gas discharge lamp is a High Intensity Discharge (HID) lamp, such as a metal halide lamp.