ASSEMBLY OF A LOW-PRESSURE SODIUM DISCHARGE LAMP AND A FEEDING APPARATUS, A LOW-PRESSURE SODIUM DISCHARGE LAMP AND A LAMP HOLDER SUITABLE FOR USE IN THE ASSEMBLY

Abstract: The assembly has a low-pressure sodium discharge lamp (1), of which the outer envelope (4) has an electrically conducting coating (5), which is connected through a capacitor (29) to one of the current supply conductors (13) to the light source (3) of the lamp (1) and to the neutral conductor (18) of the feeding apparatus (2), which supplies an alternating voltage having a frequency of at least 80 kHz. The lamp holder (23) has an eccentrically arranged projection at its inner surface while the lamp cap (6) has an eccentrically arranged recess at its outer surface, which, when the lamp cap (6) is arranged in the lamp holder (23), engage with each other and guarantee a connection of the capacitor (29) to the neutral conductor (18). The lamp (1) is suitable for operation at mains voltage frequency and is still fitting into the lamp holder of mains voltage frequency equipment.

Description: The invention relates to an assembly of a low-pressure sodium discharge lamp and a feeding apparatus, in which the low-pressure sodium discharge lamp has a light source, which is arranged in an evacuated outer envelope, whose inner surface is provided with a translucent electrically conducting coating and to which a Swan lamp cap is secured, which has at its base portion insulated contacts, from which current supply conductors extend to the light source, which light source has a discharge vessel which is filled with an ionizable sodium-containing filling, the feeding apparatus supplies an alternating voltage having a frequency of at least 80 kHz and is provided with a Swan lamp holder, which has at its base portion insulated contacts, one of which is connected to a neutral conductor and another is connected to an above ground conductor of the feeding apparatus. The invention also relates to a low-pressure sodium discharge lamp and a lamp holder suitable for use in the assembly. Such an assembly is known from GB-A-2 134 701. The known low-pressure discharge lamp can be operated at an alternating voltage having the frequency of the mains voltage (for example 50 or 60 Hz), but has a higher efficiency if it is operated at a voltage having a frequency of at least 80 kHz. It has been found that lamps operated at a voltage having such a high frequency have an electric field which disturbs radio reception. The invention has for its object to provide an assembly of a low-pressure sodium discharge lamp and a feeding apparatus, of which the radio disturbance during operation of the lamp at high-frequency voltage is suppressed, while the lamp can also be used in conjunction with a conventional feeding apparatus supplying an alternating voltage at mains frequency. According to the invention, this object is achieved in an assembly, and in a lamp suitable for use in this assembly, of the kind mentioned in the opening paragraph in that one of the current supply conductors is connected within the outer envelope of the lamp via a capacitor to the translucent electrically conducting coating, the Swan lamp cap has in its outer surface an eccentrically arranged recess, and the Swan lamp holder has at its inner surface an eccentrically arranged projection, which engages the recess in the Swan lamp cap, the said one current supply conductor being connected to the neutral conductor of the feeding apparatus. It has been found that the disturbance of radio reception is effectively suppressed when one supply conductor is connected during high-frequency operation to the translucent electrically conducting coating via a capacitor, provided that this current supply conductor is connected to the neutral conductor of the feeding apparatus. When the recess and the projection cooperating with each other are arranged eccentrically, it is quaranteed that, when the lamp is arranged in the Swan lamp holder, the neutral contact of the lamp holder gets into contact with the contact of the Swan lamp cap to which the one current supply conductor is connected. The low pressure sodium discharge lamp of the assembly according to the invention, however, is also suitable to be operated in a conventional manner at mains frequency of, for example, 50 or 60 Hz. Due to the measure taken with respect to the lamp cap of the lamp, the lamp still fits with its lamp cap into the Swan lamp holder of a conventional feeding apparatus in each of the two positions with respect to said lamp holder. Nevertheless, the lamp can be connected to a high-frequency feeding apparatus of the assembly according to the invention solely in the only correct manner in one single position. The invention therefore also relates to a low-pressure sodium discharge lamp, one of whose current supply conductors is connected within the outer envelope of the lamp via a capacitor to the translucent electrically conducting coating and to a Swan lamp cap with a recess eccentrically arranged in its outer surface. The invention also relates to a Swan lamp holder with a projection eccentrically arranged at its inner surface. In order to prevent that gas or vapour is released from the capacitor, which reduces the vacuum in the outer envelope, use is preferably made of a ceramic capacitor. In general, a capacitor of about 5 nF or more is sufficient. Radio disturbance is then suppressed to an extent which is comparable with that which is obtained when the coating is directly connected to earth. However, when the coating is earthed, this involves a very complicated structure of the lamp, inter alia an additional vacuum-tight lead-through of a conductor through the wall of the outer envelope. An embodiment of the assembly, the lamp and the lamp holder according to the invention are shown in the drawing. In the drawing: Fig. 1 shows an assembly with a lamp in side elevation and a diagrammatically indicated feeding apparatus, Fig. 2 is the plan view of the Swan lamp holder shown in Fig. 1, Fig. 3 is the bottom view of the Swan lamp cap shown in Fig. 1. In Fig. 1, the assembly comprises a low-pressure sodium discharge lamp 1 and a feeding apparatus 2, the lamp 1 having a light source 3 arranged in an evacuated outer envelope 4. The outer envelope 4 has at its inner surface a translucent electrically conducting coating 5, which reflects infrared radiation and consists, for example, of tin-doped indium oxide. A Swan lamp cap 6, which has at its base portion 7 insulated contacts 8, 9, is secured to the outer envelope 4. The light source 3 has a discharge vessel 10, which is filled with an ionizable sodium-containing filling. Electrodes 11, 12 are arranged in the discharge vessel 10. Current supply conductors 13, 14 extend therefrom to a respective contact 8, 9 at the lamp cap 6. The feeding apparatus comprises a frequency converter 15 having an input terminal 16 for connection to the neutral conductor (N) of a mains voltage source and an input terminal 17 for connection to the above ground conductor (F) thereof. The output terminals 18 (N) and 19 (F), respectively, of the frequency converter 15 are connected to the contacts 20 and 21, respectively, at the base portion 22 of a diagrammatically indicated Swan lamp holder 23, as a result of which the current supply conductor 13 of the lamp 1 is connected to the neutral conductor 18 of the feeding apparatus 2. The feeding apparatus 2 supplies an alternating voltage having a frequency of at least 80 kHz. The discharge vessel 10 is held positioned in the outer envelope 4 by a hood-shaped support 24 and by a plate 25, which has tags 26 and 27, which bear against the coating 5. By means of a bracket 28 stamped out of this plate 25, a ceramic capacitor 29 is connected mechanically and electrically to the plate 25 and is therefore also electrically connected through the tags 26, 27 to the coating 5. The capacitor 29 is connected on the other hand through a conductor 30 and the current supply conductor 13 to the neutral conductor 18 of the feeding apparatus 2. The lamp cap 6 and the lamp holder 23 of Figure 1 have the particulars, which are shown in Figures 2 and 3. In Figures 2 and 3, parts designated in Figure 1 are provided with the same reference numerals. In Figure 2, the Swan lamp holder has in its cylindrical wall portion 36 recesses 31, 31′, which are adapted to receive a respective projection 33 of the Swan lamp cap 6 (Fig. 3) and to cause it to cover therein an L-shaped path when the lamp cap 6 is arranged. The recesses 31, 31′ permit a rotation through an angle α. Unconventionally, the Swan lamp holder 23 is provided with an eccentrically arranged projection 32 at its inner surface, as a result of which conventional lamp caps do not fit any longer. In the Figure, the projection 32 is situated at the cylindrical wall portion 36. The Swan lamp cap 6 of Fig. 3 has an eccentrically arranged recess 35, which, when the lamp cap 6 is arranged in the lamp holder 23, engages the projection 32 (Fig. 2) and permits a rotation of the lamp cap 6 in the lamp holder 23 through an angle α. The recess 35 is situated in a cylindrical wall portion 34 of the lamp cap 6. The recess shown is a straight longitudinal groove, which extends from the base portion 7. However, the groove could have been L-shaped, such as 31, 31′ in Fig. 2. Due to the presence of the projection 32, the lamp cap 6 can be arranged in the lamp holder 23 only in one position, i.e. that in which the contact 8 gets into contact with the contact 20 and in which therefore the coating 5 (Fig. 1) is in connection via the capacitor 29 with the neutral conductor 18 of the feeding apparatus 2. In spite of the modification of the Swan lamp cap 6, the lamp 1 can be arranged with this lamp cap 6 in the conventional Swan lamp holder (without projection 32) of a conventional feeding apparatus supplying an alternating voltage of mains frequency, for which alternating voltage the lamp 1 is also suitable. It has been found that in an experimental arrangement a low-pressure sodium discharge lamp of 36 W emits during operation at 600 kHz a disturbance radiation, which yields an antenna voltage of 44 dB µV. If in an otherwise unchanged arrangement the electrically conducting coating of the lamp is earthed, the antenna voltage decreases to 4 dB µV and with the use of a capacitor of 10 nF in the outer envelope described to 6 dB µV. It has been found that in the experimental arrangement an antenna voltage of 24 dB µV is acceptable.

Claims: 1. An assembly of a low-pressure sodium discharge lamp (1) and a feeding apparatus (2), in which the low-pressure sodium discharge lamp (1) has a light source (3), which is arranged in an evacuated outer envelope (4), which has at its inner surface a translucent electrically conducting coating (5) and to which a Swan lamp cap (6) is secured, which has at its base portion (7) insulated contacts (8, 9), from which current supply conductors (13, 14) extend to the light source (3), which light source has a discharge vessel (10), which is filled with an ionizable sodium-­ containing filling, the feeding apparatus (2) supplies an alternating voltage having a frequency of at least 80 kHz and is provided with a Swan lamp holder (23), which has at its base portion (22) insulated contacts (20, 21), one (20) of which is connected to a neutral conductor (18) and another contact (21) is connected to an above ground conductor of the feeding apparatus (2), characterized in that one of the current supply conductors (13) is connected within the outer envelope (4) of the lamp (1) via a capacitor (29) to the translucent electrically conducting coating (5), the Swan lamp cap (6) has in its outer surface an eccentrically arranged recess (35) and the Swan lamp holder (23) has at its inner surface an eccentrically arranged projection (32), which engages the recess (35) in the Swan lamp cap (6), the said one current supply conductor (18) being connected to the neutral conductor (18) of the feeding apparatus (2). 2. A low-pressure sodium discharge lamp suitable for use in the assembly claimed in Claim 1 and provided with a light source (3), which is arranged in an evacuated outer envelope (4), which has at its inner surface a translucent electrically conducting coating (5) and to which a Swan lamp cap (6) is secured, which has at its base portion (7) insulated contacts (8, 9), from which current supply conductors (13, 14) extend to the light source (3), which light source has a discharge vessel (10), which is filled with an ionizable sodium-containing filling, characterized in that one of the current supply conductors (13) is connected within the outer envelope (4) of the lamp via a capacitor (29) to the translucent electrically conducting coating (5) and the Swan lamp cap (6) has in its outer surface an eccentrically arranged recess (35). 3. A Swan lamp holder suitable for use in an assembly claimed in Claim 1, characterized in that the lamp holder (23) has at its inner surface an eccentrically arranged projection (32).

Inventors: SPRENGERS, LEO MODESTUS
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1987
Main classification: H01J61
IPC codes: H01J61, H05B41, H01J5