WO2006000974A2

WO2006000974A2 - Low-pressure mercury vapor discharge lamp and a method for manufacture thereof

Info

Publication number: WO2006000974A2
Application number: PCT/IB2005/052007
Authority: WO
Inventors: Antonius F. H. Marijnissen; Frans J. Traksel
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-06-23
Filing date: 2005-06-17
Publication date: 2006-01-05
Also published as: WO2006000974A3

Abstract

The invention describes a low-pressure mercury vapor discharge lamp and a method for the manufacture of such a lamp. The lamp offers a more compact design compared to existing lamps, and comprises a glass vessel enclosing a discharge space, provided with at least one glass stem located within an end portion of the glass vessel, bearing an electrode arranged within the discharge space, and a container encapsulating an amount of amalgam, provided with an opening enabling gas exchange of the amalgam with the discharge space.

Description

Low-pressure mercury vapor discharge lamp and a method for manufacture thereof

The invention describes a low-pressure mercury vapor discharge lamp comprising a glass vessel enclosing a discharge space, provided with at least one glass stem located within an end portion of the glass vessel, bearing an electrode arranged within the discharge space, and a container encapsulating an amount of amalgam, provided with an opening enabling gas exchange of the amalgam with the discharge space. The invention further describes a method for the manufacture of such a low-pressure mercury vapor discharge lamp. In mercury vapor discharge lamps, mercury constitutes the primary component for the (efficient) generation of ultraviolet (UV) light. A luminescent layer comprising a luminescent material may be present on an inner wall of the discharge vessel to convert UV to other wavelengths, for example, to UV-B and UV-A for tanning purposes (sun panel lamps) or to visible radiation for general illumination purposes. Such discharge lamps are therefore also referred to as fluorescent lamps. Alternatively, the ultraviolet light generated may be used for manufacturing germicidal (UV-C). The discharge vessel of low-pressure mercury vapor discharge lamps is usually circular and comprises both elongate and compact embodiments. Generally, the tubular discharge vessel of compact fluorescent lamps comprises a collection of relatively short straight parts having a relatively small diameter, which straight parts are connected together by means of bridge parts or via bent parts. Compact fluorescent lamps are usually provided with an (integrated) lamp cap. Normally, the means for maintaining a discharge in the discharge space are electrodes arranged in the discharge space. In an alternative embodiment, the low-pressure mercury vapor discharge lamp comprises a so-called electrodeless low-pressure mercury vapor discharge lamp. The American patent US 5,294,867 describes a low-pressure mercury vapor discharge lamp known in the art. The lamp comprises a generally tubular glass vessel, provided with two glass stems bearing electrodes for the gas discharge process during operation of the lamp, located at two end portions within the discharge space of the glass vessel. The glass vessel is further provided with exhaust tubes that are used during manufacture of the lamp to fill the discharge space of the glass vessel with a gas mixture of mercury vapor and an inert gas (usually argon). An amalgam known in the art, typically a bismuth/indium alloy, is positioned at the end of one of the exhaust tubes. This main amalgam serves to stabilise the mercury pressure in the lamp during operation by absorbing mercury from the gas mixture within the lamp, depending on parameters such as temperature and partial mercury pressure within the discharge space. The exhaust tube is sealed off from the outside, creating a container of amalgam extending from the glass vessel, provided with an opening connecting to the discharge space enabling gas exchange. In the final product, the protruding non- light emitting parts of the lamp, such as electric connectors to the lamp and exhaust tubes, are usually concealed within the housing that connects the lamp with a lamp armature. In low-pressure mercury vapor discharge lamps known in the art, this armature tends to be relatively bulky. The current invention aims to enable a more compact design of low-pressure mercury vapor discharge lamps. The invention provides a low-pressure mercury vapor discharge lamp comprising a glass vessel enclosing a discharge space, provided with at least one glass stem located within an end portion of the glass vessel, bearing an electrode arranged within the discharge space, and a container encapsulating an amount of amalgam, provided with a gas opening enabling gas exchange of the amalgam with the discharge space, characterised in that the container is positioned within the discharge space. The arrangement of the container within the discharge space results in a low-pressure mercury vapor discharge lamp that has less protruding parts than low-pressure mercury vapor discharge lamps known in the art. This allows for a more flexible design of the lamp as a whole. In particular, the design freedom for the position and orientation of the electrodes within the lamp is greatly increased. Also, the non-light emitting surface part of the lamp may be smaller when compared to conventional low-pressure mercury vapor discharge lamps, which provides the possibility of more aesthetically attractive lamp designs. The discharge space of the lamp should be gas-tight in order to contain a gas mixture containing mercury vapor mixed with inert gases such as argon. The amalgam may be any mercury absorbing alloy known for use in low-pressure mercury vapor discharge lamps in the art, in particular bismuth/indium alloys. A low- pressure mercury vapor discharge lamp usually contains two electrodes, located at distal ends of the discharge space. The container may for instance be a capsule, preferably a glass capsule. The container reduces environmental risks in case the glass vessel breaks, and makes it easier to locate and recycle the amalgam from the low-pressure mercury vapor discharge lamp. It is advantageous if the container is positioned within the end portion of the glass vessel. In this way the amalgam is positioned in the vicinity the electrode. During operation of the lamp, the electrode provides heats up the amount of amalgam, resulting in evaporation of some of the mercury absorbed by the amalgam and an increased amount of mercury vapor in the discharge space, which improves the lamp performance. In a preferred embodiment, the container is positioned within the glass stem. In this way, the space within the discharge space taken up by the volume of the container is minimised, while making it easy to position the amalgam in the vicinity of the electrode. Further, the glass stem stabilises the position of the amalgam. In a preferred embodiment, the container is positioned within an exhaust tube extending within the glass discharge vessel. The exhaust tube improves the stability of the container. If the exhaust tube is integrated in the glass stem, this provides an even more compact configuration. Exhaust tubes are used for the supply of gas during manufacture of the lamp, but usually have no further use after they have been sealed off. It is preferred if the glass vessel has a tubular form, in particular a straight tubular form. The tubular form is widely used for low-pressure mercury vapor discharge lamps, and fits in standard lamp armatures. In comparison with conventional low-pressure mercury vapor discharge lamps, a lamp according to the invention may be favourable while they contain a smaller non-light emitting surface. This is in particular advantageous for straight tubular shaped low-pressure mercury vapor discharge lamps, for instance lamps generally known as TL type lamps. The standard fittings and connectors of TL type lamps offer no space outside the glass vessel that allows for the use of amalgams in these types of lamps. The invention enables the use of amalgam in tubular lamps, thus improving their stability and performance. It is preferred if the container is positioned by a supporting mount. A supporting mount prevents unwanted movement of the container by binding or restraining the container in a preferred container. The supporting mount may involve a glass connection or a glass-metal connection. In a preferred embodiment the supporting mount is a resilient element exerting a bias on a part of the lamp. Such a supporting mount offers easy positioning of the container during manufacture of the lamp, and also ensures a reliable fixation of the container in the desired position. The resilient element may for instance be prepared from a resilient material such as a resin, or the resilient element may comprise a resilient portion such as a spring element, that induces the bias on non-resilient parts of the resilient element. It is advantageous if the resilient element comprises a clip exerting a bias on a part of the lamp enclosed by the clip. Thus, the position of the container is reliably fixed. The clip or clamp may hold on to any suitable part of the lamp, for instance a protrusion of glass vessel into the discharge space such as the glass stem or an exhaust tube. In another preferred embodiment the resilient element comprises a compressed spring exerting a bias on a part of the lamp enclosing the compressed spring. Thus, the position of the container is fixed reliably. Such a resilient element is particularly suitable for attachment of the container in a confined space of parts of the lamp such as the inside of the glass vessel, the glass stem or the exhaust tube. The resilient element would then exert a bias on the inside wall of said parts. More preferably, the resilient element comprises a circular spring with an arc of more than 180°. Such a resilient element is suitable for attachment on the inside or outside of a tubular part of the lamp, for instance the glass vessel, the glass stem or the exhaust tube. It is particularly advantageous if the circular spring has an arc of approximately 360°. Such an arc offers the most reliable attachment of the container. The container may for instance be attached to the circular spring at a distal end of the circular spring wrapped around at least part of the container. The circular spring may for instance be a resilient metal or plastic strip. It is advantageous if the supporting mount comprises at least a metal part. The metal part may for instance be a metal wire or spring, which can for instance be partly molten into glas of the glass vessel or the glass stem, or which may form a clamp in order to maintain a preferred position. The metal part serves as a heat buffer, and improves heat conduction to and from the container, which improves the rapid adjustment of the amalgam temperature and thus the mercury levels within the discharge space. In a preferred embodiment the container comprises at least one separator positioned between the amount of amalgam and the gas opening. The separator may for instance be a glass rod that keeps the amount of amalgam away from the gas opening, thus ensuring that the amalgam does not spill from the container into other parts of the discharge space. The separator may span a distance from the amalgam to the gas opening from approximately 5-15 mm. In a preferred embodiment the amount of amalgam within the container is positioned at a distance of approximately 1-3 cm from the electrode, in particular 2-3 cm. At the most common operating temperatures of such an electrode, said distance provides an optimum trade-off between rapidly heating up at the start-up of the lamp, evaporating a certain amount of mercury from the amalgam into the discharge space, while at the same time the amalgam does not get too hot such that it still absorbs a certain amount of mercury to stabilize the mercury levels during operation. It is preferred if the gas opening of the container is at a larger distance from the electrode than the amount of amalgam. This stabilises the rate of evaporation from the amalgam, as the gas opening is relatively cold compared to the amalgam from which the mercury evaporates. It is advantageous if the gas opening has a diameter of approximately 0.1-0.2 mm. This size of gas opening provides sufficient gas exchange of the amalgam with the discharge space, while at the same time the gas opening is small enough to prevent unwanted spill of amalgam from the container into the discharge space. In a preferred embodiment the container is also provided with at least one depressurising opening. Due to evaporating mercury, or gas volumes trapped between the container and the amalgam, parts of the amalgam may be blown out of the container due to uncontrolled gas expansion and gas pressure build-up upon heating of the container and the amalgam. The depressurising opening provides an additional channel which reduces pressure build-up and thus prevent unwanted spill of amalgam into the discharge space. The depressurising opening may be of similar size as the gas opening, in the range of 0.1-0.2 mm. Preferably, the depressurising opening of the container is positioned opposite to the gas opening with respect to the amalgam. In this configuration, spill due to pressure build-up is most effectively suppressed. Preferably, the low-pressure mercury vapor discharge lamp is a fluorescent lamp. As typical applications of fluorescent lamps require compact stem constructions, the advantages provided by the invention are particularly attractive for fluorescent lamps. The invention also provides a method for manufacturing a low-pressure mercury vapor discharge lamp, comprising the following steps: A) arranging of at least one glass stem bearing an electrode within a discharge space of a glass vessel, B) positioning of a container encapsulating an amount of amalgam within the glass vessel, C) filling of the glass vessel with gas comprising mercury vapor through an exhaust tube extending into the discharge space, and D) sealing of the glass vessel. The use of the container makes it relatively easy and safe to handle and position the amalgam during the manufacture of the lamp. The positioning within the discharge space enables the manufacture of low-pressure mercury vapor discharge lamps with a more compact configuration. Less protruding elements extending from the glass vessel are needed, while at the same time the advantages of a stabilising amalgam are available.. In a preferred embodiment, step B) comprises the positioning of the container within the end portion of the glass vessel. The end portion of the lamp is easily accessible during manufacture of the lamp, as other elements such as the electrode are introduced here as well. Thus, this leads to easier and faster manufacture of the low-pressure mercury vapor discharge lamp. In a preferred embodiment, step B) comprises the positioning of the container within the exhaust tube. The exhaust tube of the lamp is easily accessible during manufacture of the lamp, allowing for an easier manufacture. Further, the gas stream lead through an exhaust tube has a cooling effect on the container and the encapsulated amount of amalgam. This allows for heating of the glass vessel while the container is already installed, without the risk of overheating the amalgam which may lead to loss of amalgam material. Heating of the glass vessel under a gas flow is usually performed during manufacture of the lamp in order to remove water and other impurities from the discharge space. This production step may now be performed while the amalgam is present in the tube. It is preferred when the container also has a depressurising opening, thus preventing pressure effects, as described above, upon heating resulting in unwanted spill of amalgam from the container into the discharge space.

The following two non-limiting examples will further clarify the invention. Figure 1 shows a low-pressure mercury vapor discharge lamp according to the invention. Figure 2 shows another low-pressure mercury vapor discharge lamp according to the invention. Figure 3 a and 3b show a preferred mounting of a container according to the invention. Figure 4 shows another preferred mounting of a container according to the invention.

Figure 1 shows a schematic view of a low-pressure mercury vapor discharge lamp 1 according to the invention, comprising a straight elongate tubular glass vessel 2 of the type generally know as a TL-lamp, which envelops a discharge space 3 which is filled with a gas mixture comprising gases such as argon, and mercury vapor. The glass vessel comprises two distal ends 4,5 provided with electrodes 6, 7 mounted on glass stems 8,9. The first glass stem 8 is longer than the second glass stem 9 at the opposite end of the glass vessel. Tubular exhaust tubes 10, 11 are integrated in the glass stems 8,9. A first exhaust tube 10 encloses a glass capsule 12 that encapsulates an amount of amalgam 13, for instance a bismuth- indium amalgam. The capsule 12 has a gas opening 14 with a diameter of approximately 0.2 mm, enabling gas exchange of the amalgam 13 with the discharge space 3 through the exhaust tube 10. Spill of amalgam 13 from the capsule 12 is prevented by a glass rod 15 positioned between the gas opening 14 and the amalgam 13. The length of the glass rod is 5 mm, whereas the diameter of the glass rod is approximately 1 mm, large enough to prevent the glass rod 15 from going through the gas opening 14. As the inner diameter of the glass capsule is approximately 1.25 mm, the glass rod leaves enough space between the wall of the capsule 12 for gas transport, without suffering from a capillary effect that may cause spill of liquid (molten) amalgam during manufacture or operation. The capsule 12 is mounted in the stem 8 by a metal wire 16 that is molten into the glass during manufacture of the lamp. The distance between the electrode 6 and the amalgam 13 is adjusted to a distance at which the amalgam 13 functions at an optimum at the operational temperature of the lamp. The exhaust tubes 10,11 are used during the manufacture process for filling the discharge space 3 with the appropriate gas mixture, preferably by a continuous gas flow process wherein one exhaust tube 10,11 serves as an inlet, whereas the other exhaust tube 10,11 serves as an outlet for the gas mixture. Both exhaust tubes 10,11 are arranged within the discharge space 3. During the gas filling, a gas flow cools the capsule 12 that is positioned in the gas stream, allowing for heating of the glass vessel 2 in order to remove water and impurities from the fluorescent coating 17 on the inner surface, while suppressing losses and spills due to pressure build-up in the capsule 12 in or behind the amalgam 13 that may push part of the amalgaml3 out of the capsule 12. After the gas filling, the exhaust tubes 10,11 are sealed from the outside to yield the final product. The capsule 12 is positioned within the discharge space 3, yielding a compact configuration allowing the amalgam 13 to be used in the lamp 1 without compromising light-emitting surface. In conventional low-pressure mercury vapor discharge lamps known in the art, amalgam containers protrude from the glass vessel, making it necessary to protect them by a covering or housing, which represents non- light emitting surface. The lamp according to the invention thus provides a more compact configuration that allows the use of amalgam in TL-type lamps in standard armatures without compromising light-emitting surface. Figure 2 shows a schematic view of another low-pressure mercury vapor discharge lamp 20 according to the invention, comparable to the lamp 1 in figure 1. An exhaust tube 21 is integrated in the stem 22 that bears an electrode 23. The stem 22 is positioned within the discharge space 24 of the lamp 20. A glass capsule 25 is positioned within the exhaust tube 21, firmly mounted by two metal springs 26 that through friction with the wall of the exhaust tube 21 preserve the position of the capsule 25 with respect to the electrode 23. Sufficient space between the wall of the exhaust tube21 and the outer surface of the capsule 25 remains to allow for the passage of gas. The outer end of the exhaust tube 21 is sealed gas-tight. The capsule 25 is provided with a gas opening 27 for gas exchange between the amalgam 28 within the capsule and the discharge space 24 of the lamp 20. At the opposite end of capsule 25, a depressurising opening 29 is located. This depressurising opening 29 compensates and prevents the build-up of pressure at any location within the capsule 25 that may force the amalgam 28 out of the gas opening 27 during manufacture or operation of the lamp 20. Figure 3 a shows a preferred mounting 30 of a container 31 according to the invention, wherein the supporting mount 30 is a resilient metal element exerting a bias on a tubular part 32 of the lamp, in this case the stem of the lamp shown in figure 1 or figure 2. Other parts of the lamp have been omitted for clarity. The resilient metal clip 30 is a circular spring that encloses the tubular stem 32, exerting a bias on the outside of the stem 32 and thus fixing the position of the container 31 attached to the clip. The container 31 contains amalgam and is provided with a gas opening 33 for exchange of mercury with the discharge space of the lamp. Figure 3b shows the clip 30 from figure 3a attached to the tubular stem 32, wherein it is clear that the arc enclosed by the clip covers an angle A of approximately 270°, thus leaving an opening at one side of the clip for easy attachment to the stem 32. The circular form of the clip 30 fits the profile of the tubular stem 32. A similar clip 30 could be attached to any other suitable protrusion within the discharge space of the lamp, such as an exhaust tube (see figures 1 and T). Figure 4 shows another preferred mounting 40 of a container 41 according to the invention wherein the resilient element 40 comprises a compressed circular spring exerting a bias on the inside of an exhaust tube enclosing the compressed spring. The circular spring 40 is a resilient metal strip of which one end 42 is wrapped around a tubular capsule 41 filled with amalgam, provided with a gas opening 43 for gas exchange. In this representation, some space is left between the circular spring 40 and the inside glass wall of the exhaust tube 44 for clarity, however the spring and the glass wall actually have a snug fit. The arc of the circular spring nearly spans a complete circle with an angle B of nearly 350°. This leaves a light opening 45 allowing for inward compression of the circular spring 40 in order to enable axial movement within the exhaust tube 44 during positioning of the container 42. When the spring 40 is released, bias is exerted on the inner wall of the exhaust tube 40, thus fixing the position. A similar spring 44 may be used to fix a container inside any suitable tubular element within the discharge space of the lamp. For a person skilled in the art, many different variations of a low-pressure mercury vapor discharge lamp according to the invention are possible.

Claims

CLAIMS:

1. Low-pressure mercury vapor discharge lamp (1) comprising a glass vessel (2) enclosing a discharge space (3), provided with at least one glass (8,9) stem located within an end portion (4,5) of the glass vessel, bearing an electrode (6,7) arranged within the discharge space, - and a container (12) encapsulating an amount of amalgam (13), provided with a gas opening (14) enabling gas exchange of the amalgam with the discharge space, characterised in that the container (12, 31, 41) is positioned within the discharge space.

2. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the container is positioned within the end portion of the glass vessel.

3. Low-pressure mercury vapor discharge lamp according to claim 2, characterised in that the container is positioned within the glass stem.

4. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the container is positioned within an exhaust tube extending within the glass discharge vessel.

5. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the glass vessel has a tubular form, preferably a straight tubular form.

6. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the container is positioned by a supporting mount (26).

7. Low-pressure mercury vapor discharge lamp according to claim 6, characterised in that the supporting mount is a resilient element exerting a bias on a part of the lamp.

8. Low-pressure mercury vapor discharge lamp according to claim 7, characterised in that the resilient element comprises a clip exerting a bias on a part of the lamp enclosed by the clip.

9. Low-pressure mercury vapor discharge lamp according to claim 7, characterised in that the resilient element comprises a compressed spring exerting a bias on a part of the lamp enclosing the compressed spring.

10. Low-pressure mercury vapor discharge lamp according to any of the preceding claims 7-9, characterised in that the resilient element comprises a circular spring with an arc of more than 180°.

11. Low-pressure mercury vapor discharge lamp according to any of the preceding claims 6-10, characterised in that the supporting mount comprises at least a metal part.

12. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the container comprises at least one separator positioned between the amount of amalgam and the gas opening.

13. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the amount of amalgam within the container is positioned at a distance of approximately 1-3 cm from the electrode, in particular 2-3 cm.

14. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the opening of the container is at a larger distance from the electrode than the amount of amalgam.

15. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the gas opening has a diameter of approximately 0.1-0.2 mm.

16. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the container is also provided with at least one depressurising opening.

17. Low-pressure mercury vapor discharge lamp according to claim 1, characterised in that the low-pressure mercury vapor discharge lamp is a fluorescent lamp.

18. A method for manufacturing a low-pressure mercury vapor discharge lamp (1), comprising the following steps: A) arranging of at least one glass stem (8,9) located within an end portion (4,5) of the glass vessel bearing an electrode (6,7) within a discharge space of a glass vessel, B) positioning of a container (12) encapsulating an amount of amalgam (13) within the discharge space, C) filling of the glass vessel with gas comprising mercury vapor through an exhaust tube extending into the discharge space, and D) sealing of the glass vessel.

19. A method according to claim 13, characterised in that step B) comprises the positioning of the container within the end portion of the glass vessel.

20. A method according to claim 13 or 14, characterised in that step B) comprises the positioning of the container within the exhaust tube.