WO2002035578A1

WO2002035578A1 - Electrical lighting system

Info

Publication number: WO2002035578A1
Application number: PCT/GB2001/004764
Authority: WO
Inventors: Lawrence Samuel Tyson
Original assignee: Microlights Limited
Priority date: 2000-10-27
Filing date: 2001-10-26
Publication date: 2002-05-02
Also published as: AU2002210722A1; GB0125768D0; GB0026369D0; GB2372380B; GB2372380A

Abstract

An electrical lighting system (1) having a lampholder (3) and a lamp (2), preferably a high intensity discharge lamp. Both the lamp and lampholder have respectively an electrical winding (55, 32) wound on an electromagnetic core (58, 33), the electromagnetic cores being arranged to freely disconnectably co-coperate for providing transmission of power to power the lamp by means of inductance from the lampholder. The free disconnectability enables the lamp position relative to the lampholder to be easily adjusted for the purpose of dimming and changing the focus.

Description

ELECTRICAL LIGHTING SYSTEM

The present invention relates to an electrical lighting system, and in particular to the power connections for the electrical lighting .

ampholders with exposed electrical contacts for making electrical connections to corresponding electrical contacts on lamps are known. A disadvantage of such lampholders is that the exposed electrical contacts may present a shock hazard. A further problem with known lampholders, is that as the physical size of lamps decreases, and operational voltages increase, it is difficult to obtain the necessary spacing between lamp contacts to achieve the necessary tracking and arcing distances to avoid undesirable electrical discharges occurring in the lampholder or between the lampholder and the lamp, and particular problems exist with low power high intensity discharge lamps, where high voltages are required during the ignition of the lamp.

It is desirable in electrical lighting, and particularly for High Intensity Discharge lighting, for low wattage lamps to have a high efficiency for the conversion of electrical energy into light, this is usually measured in lumens per watt. At low wattages it is difficult to make a lamp that is efficient, partly due to the difficulty of maintaining a sufficiently high temperature in a small cavity of a low wattage burner. There are heat losses by radiation from the arc and lamp envelope materials, and conduction of heat to the outside of the lamp through the external electrical connections to the electrodes.

A disadvantage of known high intensity discharge lamps that they are sealed by a 'pinch' at the closure of the glass cylinder that forms the lamp. The 'pinch' is formed by squeezing the tube flat so as to both close the glass cylinder and at the same time sealing the connectors, which typically are flat strips of molybdenum. A disadvantage of the molybdenum strips is that they are difficult to make electrical connections to, and are a source of lamp failure, as a result of corrosion of the molybdenum strips causing failure of the seal between the strips and the glass 'pinch'.

According to the present invention, there is provided an electrical lighting system including as first and second parts a lampholder and a lamp, the lampholder being arranged to receive and supply power to the lamp, wherein each part comprises an electrical winding wound on an electromagnetic core, the electromagnetic cores being arranged to disconnectably co-operate for providing transmission of power by means of inductance from the first part to the second part. A benefit of each part comprises an electrical winding wound on an electromagnetic core, is that the transfer of energy, and hence the power of the lamp, may be controlled by the design of the transformer secondary that is mounted within the lamp. Hence, in an embodiment of the invention a lampholder may be used with a range of lamp power ratings .

Preferably at least one part further comprises a magnet mounted to the electromagnetic core of the at least one part so as to induce a magnetic field in the core, the magnet and the electromagnetic cores being arranged such that when placed in close proximity to each other, the cores are retained to each other by the magnetic field.

Preferably the second part further comprises an electric lamp connected across the second electrical winding.

Preferably the second part further comprises an electrically insulating envelope arranged to fully contain the electric lamp and allow the emission of light from the lamp.

Preferably the second part further comprises an electrically insulating envelope arranged to fully contain the electric lamp and the electrical winding and the electrical connections and the electromagnetic core. A benefit of the electrically insulating envelope arranged to fully contain the electric lamp and the electrical winding and the electrical connections and the electromagnetic core, is that as there are no external electrical current carrying connections required to the lamp, a requirement for sealing an envelope where the connections pass through the wall of the envelope is eliminated .

Preferably the magnet is a permanent magnet

Preferably in a further embodiment the magnet is an electromagnet. More preferably the electrical supply to the electromagnet is direct current. Still more preferably, a permanent magnet is combined with an electromagnet .

Hence, a further benefit of the lamp having no external electrical connections, is that in an embodiment of the invention the lamp may be made with a pre-sealed glass cylinder having a moulded flat end instead of a round one. The flat end can provide the datum point from which the positions of the primary and secondary components of the transformer are measured, and likewise the position of the light source. Alignment can be assured by the selection of a suitable depth and clearances for the lamp in the lampholder. The lamp may be retained in the lampholder by a permanent magnet mounted to the lampholder, such that the lamp is subject to a magnetic field acting on the core of a transformer secondary mounted within the lamp. Such a lamp may be closed and sealed in the course of manufacture by fusing the glass cylinder at the end of the lamp away from the transformer secondary components .

A benefit of having an electromagnet is that a retentive force arising from the stationary magnetic field retaining the lamp to the lampholder maybe adjusted by adjusting the direct current supply voltage.

A benefit of combining an electromagnet and a permanent magnet is that the lamp is retained to the lampholder when the direct current supply to the electromagnet is switched off.

Preferably the lamp is a high intensity discharge lamp having electrodes for an electrical discharge.

Preferably the power to the first part is provided from a high frequency alternating current source, having a frequency greater than 400kHz.

More preferably the high frequency alternating current source is greater than 500kHz. Still more preferably the high frequency is greater than 1MHz. A benefit of high frequency is that the size of the electromagnetic cores may be reduced.

Preferably the transmission of power from the first part to the second part may be adjusted by adjusting the relative positions of the first and second part .

More preferably the adjustment of the relative positions is obtained by rotating one part axially relative to the other part about an axis common to both parts.

A benefit of the adjustment of the relative positions is obtained by rotating one part axially relative to the other part about an axis common to both parts, is that dimming of lamps may be effected by adjusting the transfer of energy between primary and secondary parts of the transformer. Since the secondary part of the transformer is within the lamp, and the primary is within the lampholder, the transfer of energy may be adjusted by mechanically adjusting the configuration of the transformer. In an embodiment of the invention this adjustment can be effected by rotating the lamp, including the secondary, to a new position relative to the primary of the transformer. A disadvantage of dimming a light source is that when operating at a lower level of light output a light source and the supply for the light is generally less efficient than when operating at the designed level of light output. This disadvantage may be reduced by controlling the transfer of energy by the said mechanical means .

Preferably in an embodiment of the invention, the lampholder has a sealed external surface on at least one face, having a recess to receive a lamp, the sealed external surface extending into the recess so as to provide a sealed surface to the recess.

A benefit of having a lampholder with a sealed external surface extending into the recess for receiving the lamp is that such a lampholder may be used in hazardous locations where exposed contacts would present a hazard. A further benefit the absence of exposed contacts is that the performance of the lampholder excludes the risk that the performance of the lampholder may be degraded by corrosion of contacts for powering the lamp.

In a preferred embodiment of the invention, there are no externally extending electrical connections passing through the electrically insulating envelope.

An advantage of the preferred embodiment is that such a lamp has fewer parts and hence may cost less to manufacture. A further advantage is that a risk of failure of the envelope seal at the place where external electrical connections are made is eliminated.

Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which :-

Figure 1 is a partially sectioned side view of a high intensity discharge lamp and a lampholder according to the invention;

Figure 2 is an enlarged cross sectional view on line AA of the lamp and lampholder shown in Figure 1, and for clarity omits a portion of the lampholder;

Figure 3 is an enlarged cross sectional view, corresponding to the view shown in Figure 2, of a second embodiment of a lampholder according to the invention;

Figure 4 is an enlarged cross sectional view, corresponding to the view shown in Figure 2, of a third embodiment of a lampholder according to the invention;

Figure 5 is an enlarged cross sectional view, corresponding to the view shown in Figure 2, of a fourth embodiment of a lampholder according to the invention;

Figure 6 is a partially sectioned side view of the high intensity discharge lamp and a lampholder shown in Figure 1 with an alternative arrangement for height adjustment;

Figure 7 is perspective view of a fifth embodiment of the invention;

Figure 7A is a partially sectioned side view of the embodiment shown in Figure 7 with a first retention arrangement;

Figure 7B is a partially sectioned side view of the embodiment shown in Figure 7 with a second retention arrangement;

Figure 8 is a side view of a partially sectioned lamp of a sixth embodiment of the invention;

Figure 8A is a front view of the same lamp shown in Figure 8, the view being perpendicular to the view shown in Figure 8; Figure 9 is an incandescent lamp, according to an embodiment of the invention, for use with any of the lampholders described with reference to the Figures 1 to 7;

Figure 10 is a further incandescent lamp according to an embodiment of the invention for use with any of the lampholders described with reference to the Figures 1 to 7;

Figure 11 is a partially sectioned side view of a high intensity discharge lamp of a seventh embodiment of the invention; and

Figure 12 is a partially sectioned side view of a high intensity discharge lamp of an eighth embodiment of the invention .

From Figure 1, a first embodiment of electrical power connections for electrical lighting 1 according to the invention may be seen. The first embodiment 1, has a high intensity discharge lamp 2 mounted to a lampholder 3. The high intensity discharge lamp comprises a sealed transparent envelope 21, formed from a tube with sealed ends 25 and 26. Mounted within the envelope is a burner 22 which has electrodes 27 and 27' and a fill 28. Connected across lead wires 29 and 29' is a surface mount ceramic capacitor 23. Lead wires 29 and 29' connect the electrodes 27 and 27 ' to a transformer secondary 24. Lampholder 3, comprises a transformer primary 31 having a primary winding 32 with leadout wires 32' and 32" mounted to a sintered ferritic core 33. Ceramic magnets 62 and 64 with their respective poles N and S, and N' and S', being north and south poles, are mounted to the ferrite core so as to induce a permanent magnetic field between the poles 38 and 39. The permanent magnetic field retains the lamp 2 to the lampholder 3. A knurled adjusting screw 36 is provided to adjust a relative height HI of the lamp 2 in the lampholder 3. Reflector 40 (shown sectioned for clarity) is mounted to the core 33, and by adjusting the relative height HI, the position of the burner 22 relative to the reflector 40 is adjusted, and hence the reflector may be arranged so that as the focus of the light from the burner reflected by the reflector is adjusted the reflected light may be adjusted from a wide beam flood light to a narrow beam spot light .

When a lamp is not fitted to the lampholder 3, the inductive impedance of the primary winding 32 of the holder will be low, since an effective magnetic path length is greatly increased due to the large air gap present in magnetic circuit. When a lamp is fitted as shown in Figure 1, the air gap in the magnetic core 33 is reduced by the magnetic core 58 of the lamp. Hence the inductive impedance of the primary winding 32 of the holder will be increased. For the embodiment shown in Figure 1, where the lamp is a high intensity discharge lamp, an application of electrical power to a suitable ballast connected to leadout wires 32' and 32" will produce a high resonant ignition current if the lamp is present, but will not produce such resonant current if the lamp is absent, due to the lower impedance of the primary winding in this case. Preferably the ballast is provided with a peak current detector such in its output circuit, such that it may detect the presence or absence of the high resonant voltage associated with lamp ignition. Preferably the ballast is arranged to shut down if the high resonant voltage does not occur, hence preventing undesirable continued operation of the ballast .

A suitable ballast for the provision of electrical power to the embodiment shown in Figure 2 would be that disclosed in our British patent number GB 2,344,004.

From Figure 2, an enlarged view of part of Figure 1, the transformer secondary 24 may be seen to comprise a magnetic core 58 having two poles 52 and 54, separated by a groove 53 into which the secondary winding 55 is placed, with leadout wires 56 and 56' which are connected to lead wires 29 and 29' shown in Figure 1. The transformer secondary is a close fit within the tubular portion of the envelope 21. The poles 38 and 39 of the transformer primary 31 are also a close fit to the outside of the same tubular portion of the envelope 21. Figure 6 shows the same partially sectioned side view of the high intensity discharge lamp 2 as shown described with reference to Figure 1 and a similar lampholder 603 but with an alternative arrangement for height adjustment. Lampholder 603, comprises a transformer primary 631 having a primary winding 632 with leadout wires 632' and 632" mounted to a sintered ferritic core 633. Ceramic magnets 662 and 664 with their respective poles N and S, and N ' and S', being north and south poles, are mounted to the ferrite core so as to induce a permanent magnetic field between the poles 638 and 639. The permanent magnetic field retains the lamp 2 to the lampholder 603. Mounted to the core 633 are direct current windings 637 and 637 ' . The direct current windings 637 and 637 ' are connected in series and in anti-phase such that the effect of an alternating current voltage induced in coil 637 by a changing flux in the core 633 is cancelled by the corresponding alternating current induced in coil 637'. When connected in this manner, a direct current applied through the two series connected coils 637 and 637' will produce a standing magnetic field in the core 633 that is the sum of the individual magnetic fields produced by each coil 637 and 637'. In operation, this said standing magnetic field depending on the polarity of the applied direct current will increase or decrease the effect of the magnetic field arising from the permanent magnets 662 and 664. A 1 '

spring 636 is mounted between the lamp 2 and the core 633 so that the spring applies a force to the lamp urging the lamp out of the lampholder against the effect of the magnetic field from the permanent magnets 662 and 664. As in Figure 1, reflector 640 (shown sectioned for clarity) is mounted to the core 633, and by adjusting the relative height H6, the position of the burner 22 relative to the reflector 640 is adjusted, and hence the reflector may be arranged so that as the focus of the light from the burner reflected by the reflector is adjusted the reflected light may be adjusted from a wide beam flood light to a narrow beam spot light.

A benefit of the arrangement shown in Figure 6, is that the focus of the lamp may be adjusted remotely from the lamp, while the lamp is lit. This would be of particular use for example where lamps and lampholders are mounted at high level, or for lamps used in stage lighting.

It should be noted that the application of the direct current to the coils 637 and 637 ' producing the standing magnetic field in the ferrite core 633 will reduce the permeability of the ferrite core to the alternating magnetic field produced by the alternating current flowing in coil 632. To ensure that this effect does not affect the normal operation of the lamp by the high frequency power transfer, it is necessary to increase the size of the ferrite core to compensate. For example an increase in size of approximately 15% in cross sectional area of the ferrite core is adequate for magnets of sufficient strength to retain the lamp in the lampholder.

The high intensity discharge lamps shown and described with reference to Figures 1 require for operation a high frequency alternating current supply to the primary winding 32 of the transformer. Such a suitable high frequency generator would operate at a frequency preferably above 400kHz, and more preferably above 500kHz. In operation the high frequency generator is connected across the transformer primary winding 32 to power the lamp 2 in the lampholder 3. The high frequency generator is preferably capable of producing a sweep across a range of frequencies to cause the secondary winding to resonate with capacitor 23 to create a resonant high voltage across the lamp electrodes 27 and 27 ' sufficient to cause the fill 28 to begin to conduct electricity. Once the lamp has lit, and has an electrical discharge established between the electrodes 27 and 27', the high frequency generator is preferably arranged to adjust the frequency of the supply to the transformer primary 32 so as to operate a running frequency. The characteristics of the lamp and its associated secondary winding should be such that the power input into the lamp from the primary winding and the associated components of the lampholder ensure the lamp operates at a desired power level when lit.

A benefit of operating at a high frequency is that component size is reduced and adequate power transfer may be made possible with components of a size that may be fitted within a lamp.

The operation of the other high intensity discharge lamps described with reference to the Figures 2 to 8, and 11 and 12, are similar.

Figures 3, 4 and 5 show further embodiments of the invention in a plan view and are generally similar to the embodiments already described above with reference to Figures 1, 2 and 6. In each of these Figures the lamp 302, 402 and 502 is preferably closely similar or identical to the lamp 2 in Figure 1 described above. The embodiments of Figures 3, and 4 show alternative arrangements for dimming the lamp by altering the orientation of the lamp 302 and 402, and hence the transformer secondary 324 and 424 with respect to the transformer primary winding (which is not shown in these figures, but is as described with reference to Figures 1 and 6) . By altering the relative orientation of the transformer primary and transformer secondary the effective transfer of power from the primary winding to the secondary winding may be controlled, and hence the lamp dimmed.

In the second embodiment shown in Figure 3, a flanged collar 380 is mounted to a lamp 302 so as to be able to impart an angular displacement to the lamp. The flanged collar has a flange 381 extending away from the lamp, having a arcuate slot 382 to receive a clamping screw 383 to lock the flange 381 at a particular desired angle relative to the primary 331 and its magnetic core 333. As shown in Figure 3, the lamp is in a position to operate at a maximum power, but when the flange 381 is moved in direction of arrow 3R the lamp power will be reduced and the lamp will dim. For the lamp to operate at maximum power primary poles 338 and 339 must be aligned with secondary poles 352 and 354 of a magnetic core 358 and winding 355 of the lamp 302 as shown in the Figure 3.

In the third embodiment 401 shown in Figure 4, a toothed collar 480 is mounted to the lamp 402 having a magnetic core 458 and a winding 455. When the lamp 402 is mounted to lampholder 403 the toothed collar 480 engages with detent 484 mounted on resilient arm 482 which is mounted by screw 486 to the ferrite core 433 of the lampholder

403. To adjust lamp brightness, the lamp 402 is rotated in the direction of arrow 4R so that the detent engages between an alternative pair of teeth. Permanent magnets 462 and 464 induce a stationary magnetic field in the ferrite core 433 to act to retain the lamp in the lampholder .

In either of the embodiments shown in Figure 3 or , the lamps may be dimmed while lit or adjusted while they are not lit. Further either of the dimming arrangements may 1.

be combined with either of the focusing arrangements described with reference to Figures 1 and 6. In the case of Figure 3, the extending flange 381 should be arranged so that it is flexible to permit the desired axial focussing movement of the lamp.

The lamp may be arranged so that ignition of the lamp is not adversely affected by the rotation necessary in the second and third embodiments to dim the lamp. It should be noted that the initiation of ignition of such high intensity discharge lamps is dependent on a high voltage being generated, rather than by a high current.

Figure 5 shows a fourth embodiment 501 of the invention, with a lamp 502 and a lampholder 503. The lamp 502 is preferably closely similar or identical to the lamp 2 described above, having a magnetic core 558 and a winding 555. The lampholder 503 comprises a transformer primary 531 having an ferritic core 533 formed as an annular ring having two poles 538 and 539 extending inwards from the ring towards the lamp 502. The ferritic core 533 has two windings 532 and 532'. Preferably these are identical, and are connected in series and arranged so that when supplied with an alternating current supply they produce an alternating magnetic field across the poles 538 and 539. A permanent magnet 560 is arranged so that it produces a magnetic field across poles 562 and 564. In operation the fourth embodiment is similar to that described with reference to Figures 1 to , and may be dimmed by rotating the lamp in the direction of arrow 5R by, for example, either of the arrangements shown in Figures 3 or 4.

The fourth embodiment of Figure 5, may also be focused by using the screw arrangement of Figure 1, or by the spring arrangement of Figure 6. In the case of the spring arrangement of Figure 6, a direct current supply may be superimposed on the windings 532 and 532' to produce a stationary magnetic field across the poles 538 and 539.

Figure 7 shows a perspective view of a fifth embodiment 701 of the invention, and Figure 7A and Figure 7B show partially sectioned side views of the same embodiment with alternative mounting means (not shown in Figure 7) . The fifth embodiment 701 comprises a lamp assembly 704 having a lamp 702 mounted to a reflector 740 by means of mounting 775. The lamp 702 has a transformer secondary 724 comprising a magnetic core 758 having two poles 752 and 754, separated by a groove into which the secondary winding 755 is placed, the transformer secondary is a close fit within the tubular portion of the envelope 721. The lampholder 703 comprises a transformer primary 731 formed from an indefinite length of ferrite extrusion 733 with a primary winding 732 formed as a single turn of wire in close contact with the extrusion along its length. The lamp assembly 704 is arranged such that it may be mounted at any desired location along the length of the extrusion 733. In operation a high frequency supply, similar to that mentioned with reference to Figure 1 is arranged to provide electrical power to the primary winding 732.

Preferably the mounting 775 is arranged to allow position of the lamp 702 relative to the reflector 740 to be adjusted in both an axial direction and an angular direction. Hence, by adjusting the lamp in an angular direction dimming of the lamp may be effected, and by adjusting the lamp in an axial direction, a height H7, and hence the focusing of the lamp may be adjusted.

Figure 7A shows a first alternative means 701A of mounting the lamp assembly 704A to the lampholder track 703. The first alternative means comprises a pair of resilient clips 771 and 773 mounted to the reflector 740 at 772 and 774. The resilient clips resile so as to allow the lamp assembly to be mounted onto the lampholder track and once mounted the resilient clips locate on the core 733 so as to retain the lamp assembly to the lampholder track. A benefit of the first alternative means is that when a number of lamps are mounted to the track at a time, the lamps do not affect the magnetic permeability of the core to the high frequency supply that is connected to the primary winding 732. Figure 7B shows a second alternative means 701B of mounting the lamp assembly 704B to the lampholder track 703. The second alternative means comprises an annular permanent magnet 780 having an internal cylindrical surface 784, and external cylindrical surface 783, a flat face 781 for abutting the core 733, and a concave face 782 for mounting to the reflector 740. Adhesive 785 retains the magnet 780 to the reflector 740.

The magnet is preferably magnetised so that face 781 is one pole and face 782 is another pole.

A benefit of the arrangement of the second alternative means 701B, is that the reflector, and hence the lamp may be rotated, thus effecting dimming of the lamp, while the lamp is lit.

A benefit of the track lampholder shown in Figure 1 , is that the lampholder may be arranged such that more than one lamp may be mounted to the lampholder according to the length of the lampholder.

With the track lampholder, dimming may be effected for lamps individually. Further, lamps of different power ratings may be powered from a track lampholder, provided that the maximum load is within a maximum design load of the track lampholder.

A further benefit is that lamps may be inserted and removed from the track while the track is powered. However, when such lamps are high intensity discharge lamps, they will not light until the power supply to the track provides a suitable frequency sweep to generate the required high resonant ignition voltage for the lamps .

Figure 8 and Figure 8A show a sixth embodiment 801 of a high intensity discharge lamp according to the invention. The high intensity discharge lamp comprises a sealed transparent envelope 820, formed from a tube with sealed ends 825 and 826. Mounted within an upper tubular portion 821 of the envelope 820 is a burner 822 which has electrodes 827 and 827' and a fill 828. Lead wires 829 and 829' pass through a pinch seal 880 and connect the electrodes 827 and 827' to a transformer secondary 824. Pinch seal 880 is formed by deforming the tube when it has been softened by the application of heat, such that the internal surface 881 fuses to itself in the pinch seal region 883. Connected across lead wires 829 and 829' is a surface mount ceramic capacitor 823. The transformer secondary 824 comprises two poles 852 and 854, separated by a groove 853 into which the secondary winding 855 is placed, with leadout wires 856 and 856' which are connected to lead wires 829 and 829' . The transformer secondary is a close fit within a lower tubular portion of the envelope 881. The lower tubular portion 881 is preferably the same diameter as the tubular portion 21 of the envelope 820.

A benefit of the sixth embodiment shown in Figure 8 is that the pinch seal between the upper and lower tubular portions may improve lamp life, by preventing any release of contaminants from the transformer secondary from contaminating the upper tubular portion containing the burner .

The sixth embodiment has a further benefit in that the size of the tubular portion containing the burner is reduced, and the transformer secondary is protected from the heat of the burner when the lamp is lit by the pinch 880. Hence the lamp life may be maintained by the cooler operation of the transformer, and the efficiency of the lamp will be improved by the reduced heat losses from the burner .

In operation the sixth embodiment 801 may be mounted to any of the lampholders described with reference to the above Figure 1 to 7 , 7A and 7B, and will operate in a manner similar to that described with reference to the lamps of those Figures. Figure 9 shows an incandescent lamp 901, having an incandescent filament 902 supported by lead wires 904 and 905. Lead wire 904 is connected by lead 906, to a secondary winding 955 on the magnetic core 958 of transformer secondary 924. The other end of winding 955 is connected to lead wire 905, forming a series circuit with the incandescent filament 902. The transformer secondary has two poles 952 and 954, which are a close fit within the tubular portion 921 of the envelope 920. The envelope is sealed at each end 925 and 926. In operation the lamp 901 is mounted to a lampholder as described with reference to Figures 1 to 7, and a high frequency supply is connected to the primary of the lampholder to provide power for operating the lamp. As described above, the lamp 901 may be dimmed by an angular displacement with respect to the lampholder to which it is mounted.

Figure 10 shows an incandescent lamp 100] , having an incandescent filament 1002 and is similar to the lamp described with reference to Figure 9, apart from the reflector 1040 permanently mounted to the lamp envelope 1020. The lamp envelope 1020 is sealed at each end 1025 and 1025. A benefit of the reflector 1040 permanently mounted to the lamp envelope is that a manufacturer may closely control the focus of the lamp to obtain desired lamp characteristics. Figure 10 also shows a permanent magnet 1050 mounted to the electro-magnetic core 1058 of the lamp 1001 so as to produce a permanent magnetic field that is sufficient to retain the lamp to a lampholder, such as lampholder 703 where no permanent magnet is mounted to the lampholder.

From Figure 7, a magnetic field detector, such as reed switch 790 is mounted to the lampholder 703 adjacent to a lamp 701B to detect the presence of the lamp by detecting the magnetic field arising from the permanent magnet 780. Such a detector has a low frequency response, and may be used to detect the permanent magnet field, but not be affected by the high frequency alternating field used for power transmission to the lamp.

Figure 11 shows a seventh embodiment 111 of a high intensity discharge lamp according to the invention. The high intensity discharge lamp comprises a sealed transparent envelope 112, formed from a tube 113 with sealed ends 115 and 116. Mounted within the tubular portion 118 of the envelope 112 is a burner 122 which has electrodes 127 and 127' and a fill 128. Lead wires 129 and 129' connect the electrodes 127 and 127' to a capacitor 123 and a transformer secondary 124. The transformer secondary 124 comprises two poles 152 and 154, separated by a groove 153 into which the secondary winding 155 is placed. The lamp 111 is assembled by inserting the capacitor and transformer secondary already connected to the burner into the tube 113 which has already been formed with the flat end 116, a potting material 130 is then added to the tube so as to fill the tube and cover at least the transformer secondary. More preferably the potting compound also covers the capacitor 123.

A benefit of the seventh embodiment shown in Figure 11 is that the potting compound covering the transformer may improve lamp life, by preventing any release of contaminants from the transformer secondary from contaminating the upper tubular portion 125 containing the burner.

The seventh embodiment has a further benefit in that a volume of the upper tubular portion containing the burner is reduced, and the transformer secondary is protected from the heat of the burner when the lamp is lit. Hence the lamp life may be increased by the cooler operation of the transformer, and the efficiency of the lamp may be improved by the conservation of heat that would otherwise be lost from the lamp. Figure 12 shows a seventh embodiment 211 of a high intensity discharge lamp according to the invention. The high intensity discharge lamp comprises a sealed transparent envelope 212, formed from a tube 213 with sealed ends 215 and 216. A tubular cap 260 formed with a sealed end 262 is mounted to the sealed transparent envelope 212 at 264. Mounted within the tubular portion 218 of the envelope 212 is a burner 222 which has electrodes 227 and 227' and a fill 228. Lead wires 229 and 229' connect the electrodes 227 and 227' to a capacitor 223 and a transformer secondary 224. The transformer secondary 224 comprises two poles 252 and 254, separated by a groove 253 into which the secondary winding 255 is placed. Sealed end 216 comprises a pinch seal through which the lead 229 and 229' wires pass. An upper space 225 is filled with an inert gas.

Preferably the sealed envelope 212 and the cap 260 are made of a similar glass material which may be joined with a glass frit at 264 to form a lower sealed space 265 that may be filled with an inert gas.

A benefit of the seventh embodiment shown in Figure 12 is that the pinch seal at sealed end 216 may improve lamp life, by preventing any release of contaminants from the transformer secondary from contaminating the upper sealed space 225 containing the burner. The seventh embodiment has a further benefit in that a volume of the upper tubular portion containing the burner is reduced, and the transformer secondary is protected from the heat of the burner when the lamp is lit. Hence the lamp life may be increased by the cooler operation of the transformer, and the efficiency of the lamp may be improved by the conservation of heat that would otherwise be lost from the lamp.

A yet further benefit of the seventh embodiment is that the sealed cap filled with an inert gas protects the wires passing through the pinch seal from corrosion.

A benefit of the wires passing through the pinch seal being protected from corrosion and of the inert gas fill to both space 225 and 265, is that it may be possible to provide a satisfactory seal without the use of a molybdenum foil, and hence manufacturing costs may be reduced.

Although the cap 260 in Figure 12 is preferably of a glass material, other materials may provide further advantages. Such other materials may include ceramics and plastics materials. In operation the embodiments of Figures 11 and 12, may be mounted to any of the lampholders described with reference to the above Figure 1 to 7, and will operate in a manner similar to that described with reference to the lamps of those Figures.

References to a ferritic or ferrite material for the core of the transformer, are to include other suitable materials with similar properties. Such materials are known as soft magnetic materials .

Claims

1. An electrical lighting system including as first and second parts a lampholder and a lamp, the lampholder being arranged to receive and supply power to the lamp, wherein each part comprises an electrical winding wound on an electromagnetic core, the electromagnetic- cores being arranged to disconnectably co-operate for providing transmission of power by means of inductance from the first part to the second part .

2. An electrical lighting system as claimed in claim 1, wherein at least one part further comprises a magnet mounted to the electromagnetic core of the at least one part so as to induce a magnetic field in the core, the magnet and the electromagnetic cores being arranged such that when placed in close proximity to each other, the cores are retained to each other by the magnetic field.

3. An electrical lighting system as claimed in claim 2, wherein the second part further comprises an electrically insulating envelope arranged to fully contain the electric lamp and the electrical winding and the electrical connections and the electromagnetic core .

4. An electrical lighting system as claimed in any of the preceding claims, wherein the lamp is a high intensity discharge lamp having electrodes for an electrical discharge .

5. An electrical lighting system as claimed in any of the preceding claims, wherein the power to the first part is provided from a high frequency alternating current source, having a frequency greater than 400kHz.

6. An electrical lighting system as claimed in any of the claims from 2 to 5, wherein the magnet comprises a permanent magnet.

7. An electrical lighting system as claimed in any of the claims from 2 to 6, wherein the magnet comprises an electro-magnet .

An electrical lighting system as claimed in any of the preceding claims, wherein provision is provided for the first part and the second part to be adjusted relatively .

9. An electrical lighting system as claimed in claim 8, wherein the relative adjustment is obtained by rotating one part axially relative to the other part about an axis common to both parts .

10. An electrical lighting system as claimed in claim I or 9, wherein the relative adjustment is obtained by moving one part linearly relative to the other part along an axis common to both parts.

11. An electrical lighting system as claimed in any of the preceding claims, wherein the lampholder has a sealed external surface on at least one face, having a recess to receive a lamp, the sealed external surface extending into the recess so as to provide a sealed surface to the recess.

12. An electrical lighting system as claimed in claim 13, wherein there are no externally extending electrical connections passing through the electrically insulating envelope.

13. An electrical lighting system as claimed in any of claims 8 to 12 when dependent on claim 2, wherein an adjustment of a magnetic field generated by the electro-magnet is arranged to adjust the relative positions .

14. An electrical lighting system as claimed in any of claims 8 to 13, wherein the relative adjustment is arranged to adjust a level of power transmitted from the first part to the second part.

15. An electrical lighting system substantially as hereinbefore described and with reference to the accompanying drawings.