WO2013008144A1

WO2013008144A1 - Discharge lamp, tube for the discharge lamp and method of manufacturing thereof

Info

Publication number: WO2013008144A1
Application number: PCT/IB2012/053413
Authority: WO
Inventors: Adam Tomasz POLAK
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-07-14
Filing date: 2012-07-04
Publication date: 2013-01-17

Abstract

The present invention provides a discharge lamp, a tube for the discharge lamp, a method of manufacturing the tube and a method of manufacturing the discharge lamp. The discharge lamp comprises: a tube(310)comprising a first twisted part(311)which has a first twist axis (1),and a base(320)having a central axis (2), the tube(310)being connected to the base(320)along the central axis (2),wherein the angle between the first twist axis (1) and the central axis (2) of the base is in the range [45°, 90°]. Thus, high flexibility for shaping the twisted tube for the discharge lamp is provided. Preferably, the shape of the tube is spherical so as to provide a homogenous light distribution. The tube preferably further comprises a second twisted part which has a second twist axis (1'); the first axis (1) and the second axis (1') do not overlap,and the second twisted part of the tube is communicatively connected with the first twisted part of the tube.

Description

DISCHARGE LAMP, TUBE FOR THE DISCHARGE LAMP AND METHOD OF MANUFACTURING THEREOF

FIELD OF THE INVENTION

The invention relates to illumination, in particular to a discharge lamp, a tube for the discharge lamp, a method of manufacturing the tube, and a method of manufacturing the discharge lamp. BACKGROUND OF THE INVENTION

Compared to general lighting service (GLS) incandescent lamps, discharge lamps offer a longer service life and higher efficiency. The best known discharge lamp is perhaps the compact fluorescent lamp (CFL), also known as compact fluorescent light or energy saving light.

In particular, an integrated compact fluorescent lamp (CFL-i) allows consumers to replace the incandescent bulb in many standard incandescent light fixtures, reducing the cost of converting to fluorescent. A standard CFL-i usually comprises a burner (also called gas- filled tube or bulb) having a cylindrical or conoidal shape, which is achieved either by interconnecting two or more U-shaped tubes or by using a twist shape tube. The twist shape is a helix or double helix. For example, Fig. la shows a CFL-i with a cylindrical burner including three U-shaped tubes 111 and a base 112; Fig. lb shows a CFL-i burner including a tube 121 in the shape of a cylindrical double helix and a base 122; Fig.lc shows a CFL-i burner including a tube 131 in the shape of a conical double helix and a base 132.

The efficiency of the CFL-i is much higher than that of the GLS incandescent bulb, but some of its parameters still do not meet the expectations of customers who have been used to the light generated by GLS incandescent bulbs.

Nowadays, as incandescent bulbs are sequentially, type-by-type, banned from the market due to their very low efficiency, it becomes more crucial to provide a replacement for incandescent bulbs in the form of other kinds of light sources which do meet customers' expectations. SUMMARY OF THE INVENTION

The inventor of the present invention has recognized the following disadvantages of the existing discharge lamp described above.

Firstly, burners with twist shape tubes are the largest category in the CFL-i product family, but the shape of such burners is very limited. As shown in Figs.lb-lc, the twist shape tube 121 , 131 is either cylindrical or conoidal; the twist shape tube rotates about a twist axis 1 and translates along the twist axis 1 simultaneously; and the twist axis 1 of the twist shape tube is substantially aligned with the central axis 2 of the base 122, 132. Such a shape limitation results in disadvantages in many aspects.

In one aspect, the light distribution of a cylindrical or conoidal burner is highly deformed as compared to the homogenous, almost spherical light distribution of a GLS incandescent bulb. In the case of the cylindrical or conoidal burner, luminescence is highly directed to the top and the side of the burner, and only a limited amount of light is directed to the bottom of the burner, which makes the light distribution highly inhomogeneous.

In another aspect, when cylindrical or conoidal burners are arranged in an outer bulb, the space inside the outer bulb cannot be fully utilized if the shape of the outer bulb is not cylindrical or conoidal. The shape of the outer bulb can vary according to the requirements with respect to light distribution and/or bulb design. For example, many customers have got used to the outer bulb of GLS A55 or A60 shape. Figs.2a-2b show a cylindrical burner and a conoidal burner arranged in an outer bulb of GLS A55 shape, respectively. Referring to Fig.2a, lateral space inside the GLS A55 outer bulb 213 is not utilized when the bulb accommodates a cylindrical burner 211. Referring to Fig.2b, bottom space inside the GLS A55 outer bulb 223 is not utilized when the bulb accommodates a conoidal burner 221. For an outer bulb of given shape, the more space inside the outer bulb is utilized, the greater the total length of the tube is and hence the higher the luminous flux that can be achieved. In other words, for an outer bulb of given shape, the size of the outer bulb can be reduced without reducing the luminous flux when more space inside the outer bulb is utilized.

Secondly, it is very difficult to manufacture a twist shape tube in shapes other than cylindrical or conoidal. In the manufacturing process of the twist shape tube, a mould is required for bending the tube so as to be twist shaped. Since the mould has to be evacuated eventually from the twist shape tube, the diameter at the bottom of the twist shaped tube must be wider than or at least the same as the other tube portions. Thus, for example, a spherical, twisted tube cannot be easily manufactured by means of direct twisting in the mould. As a result, for an existing CFL-i comprising a twist shape tube and a base, the twist shape tube is either cylindrical or conoidal, and the twist axis of the twist shape tube substantially coincides with the central axis of the base.

Based on the understanding of the technical problems described above, it would be desirable to reduce the limitations of the shape of the twist shape tube for a discharge lamp so as to provide twist shape tubes of various shapes. It would also be desirable to provide a discharge lamp capable of providing a homogeneous light distribution. It would also be desirable to provide a discharge lamp capable of efficiently using the space inside an outer bulb of any shape, enabling the luminous flux to be increased without the size of the outer bulb having to be enlarged.

To better address one or more of the above concerns, according to an embodiment of a first aspect of the invention, a discharge lamp is provided. The discharge lamp comprises: a tube comprising a first twisted part which has a first twist axis; and

a base having a central axis, the tube being connected to the base along the central axis; wherein an angle between the first twist axis and the central axis of the base is in the range [45°, 90°].

Unlike the existing discharge lamp, the first twist axis of the first twisted part according to an embodiment of the invention is not aligned with the central axis of the base any more. This provides high flexibility with respect to the shaping of the twisted tube for the discharge lamp.

Preferably, the tube comprising the first twisted part is substantially spherical. Thus, more homogeneous light distribution can be achieved.

In another embodiment, the tube of the discharge lamp further comprises a second twisted part which has a second twist axis; the first axis and the second axis do not overlap; and the second twisted part of the tube is communicatively connected with the first twisted part of the tube.

By allowing the tube to have more than one twist axis, high flexibility with respect to the shaping of the twisted tube for the discharge lamp is further provided. For example, the tube comprising the first and the second twisted parts can also be substantially spherical. Thus, a more homogeneous light distribution can be achieved. According to an embodiment of a second aspect of the invention, a tube for a discharge lamp is provided. The tube comprises:

a first twisted part which has a first twist axis; wherein

two ends of the tube are connectable to a base of the discharge lamp along a central axis of the base; and

an angle between the first twist axis and the central axis of the base is in the range [45°,

90°].

According to an embodiment of a third aspect of the invention, a method of manufacturing a tube for a discharge lamp is provided. The method comprises a step of:

forming a twisted tube by twisting a first tube around a first twist axis;

wherein two ends of the twisted tube are connectable to a base of the discharge lamp along a central axis of the base, wherein an angle between the first twist axis and the central axis of the base is in the range [45°, 90°].

In another embodiment, the step of forming a twisted tube further comprises substeps of:

twisting a second tube around a second twist axis (1 '); and

communicatively connecting the first tube and the second tube to form the twisted tube.

In another embodiment, the first tube and the second tube are made of glass; and the first tube and the second tube are communicatively interconnected by means of front fusing.

In this manner, the two tubes, after being interconnected, almost appear to be a single twisted tube.

Preferably, the method further comprises the following step to be carried out before the interconnecting substep: covering the inner side of each of the first tube and the second tube with a fluorescent powder.

In the case of a fluorescent lamp, the inner side of the tube is to be covered with fluorescent powder. Interconnecting the two tubes after covering them with a fluorescent powder is especially advantageous in some cases. Typically, to cover the tube with fluorescent powder, the tube solution is first flushed through the tube and then the tube is suspended to allow excessive fluorescent solution to flow out of the tube, which is suitable for twisted tubes in shapes such as cylindrical, conoidal and semi-spherical. However, for some shapes of the twisted tube, such as a spherical shape according to an embodiment of the present invention, it is difficult to cause the excessive fluorescent solution to flow out of the tube by suspending the tube. Thus, it would be advantageous to perform the covering step before the interconnecting substep.

Preferably, the method further comprises the following step after the interconnecting substep: sintering the fiuorescent powder.

From a realizability point of view, the step of sintering can be performed either before the interconnecting substep or after the interconnecting substep, but the latter is more efficient in process flow. However, the step of sintering the fluorescent powder can be performed before the interconnecting substep. As is well-known, the sintering procedure is performed at a high temperature. Thus, the tube should be cooled before carrying out the interconnecting substep. According to standard procedures well known in glass processing, annealing is applied to the interconnected glass tubes such that the connection can be resistant to cracking or shattering when subjected to a relatively small temperature change or mechanical shock. In the annealing process, the glass is heated until the temperature reaches a stress-relief point, i.e. the annealing temperature. As a result, the tubes are first heated for sintering the fluorescent powder, then cooled for interconnecting them, and then heated again for the annealing process. In other words, the tubes are heated twice. On the other hand, when the step of sintering of the fluorescent powder is performed after the interconnecting substep, the sintering procedure and the annealing process are two successive steps, and therefore, it is not necessary to heat the tubes twice, which makes the manufacturing process more efficient.

In another embodiment, the method further comprises a step of deforming the two ends of the twisted tube so as to be connectable to a base of the discharge lamp along the central axis of the base. When the twisted tube is formed by communicatively interconnecting two twisted tubes, such a step of deforming can be performed either before or after the interconnecting step.

According to an embodiment of a fourth aspect of the invention, a method of manufacturing a discharge lamp is provided. The method comprises a step of manufacturing a tube as described above, and a step of connecting the tube to the base along the central axis of the base.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention will become more apparent from the following detailed description considered in connection with the accompanying drawings, in which:

Figs.la-lc each depict a schematic diagram of a CFL-i according to the prior art; Figs.2a-2b each depict a schematic diagram of a CFL-i arranged in a classic GLS outer bulb according to the prior art.

Fig.3a depicts a front view of a tube and a base of a discharge lamp in accordance with an embodiment of the present invention; Fig.3b depicts a side view of the tube and the base in Fig.3a;

Fig.4a depicts a schematic diagram of a tube arranged in a GLS A55 outer bulb in accordance with an embodiment of the present invention; Fig.4b is a cross-sectional view of the tube disposed in the GLS A55 outer bulb in Fig.4a;

Fig.5a depicts a front view of a tube and a base of a discharge lamp in accordance with an embodiment of the present invention; Fig.5b depicts a top view of the tube and the base in Fig.5a; Fig.5c depicts a side view of the tube and the base in Fig.5a;

Fig.6a depicts a perspective view of a tube and a base of a discharge lamp in accordance with an embodiment of the present invention; Fig.6b depicts a top view of the tube and the base in Fig.6a; Fig.6c depicts a side view of the tube and the base in Fig.6a;

Fig.7 depicts a flow chart of a method of producing a tube for a discharge lamp in accordance with an embodiment of the present invention; and

Figs.8a-8f depict a procedure for producing a gas-filled tube with electrodes for a discharge lamp in accordance with an embodiment of the present invention.

The same reference numerals are used to denote similar parts throughout the Figures.

DETAILED DESCRIPTION

A detailed description of the present invention is given below with reference to the accompanying drawings. Fig.3a depicts a front view of a tube and a base of a discharge lamp in accordance with an embodiment of the present invention; Fig.3b depicts a side view of the tube and the base in Fig.3a.

Referring to Fig.3, the tube 310 comprises a substantially spherical, twisted part 31 1 having a twist axis 1. The twist axis is known as a directed line in space, along which a translation occurs, and about which rotation occurs. The two ends 313 of the tube 310 are formed so as to be connectable to a base 320 along a central axis 2 of the base 320. Moreover, when the tube 310 is connected to the base 320, the twist axis 1 is substantially perpendicular to the central axis 2 of the base 320. For example, as shown in Fig. 3, two ends 313 of the tube 310 form a plane; the central axis 2 of the base 320 is situated in said plane, and the twist axis 1 of the tube 310 is substantially perpendicular to said plane, so that, in other words, the twist axis 1 of the tube 310 and the plane form an angle of about 90 °.

The twisted part 311 can be formed in different ways. In an embodiment, the twisted part 311 can be formed by twisting a tube into a spherical shape with twist axis 1. In another embodiment, the twisted part 311 is made of a first twisted part and a second twisted part, which are two identical, semi-spherical, twisted parts that are communicatively connected with each other. The two twisted parts are interconnected in such a way that their twist axes substantially overlap one another.

As shown in Fig.3, the twisted part 311 is substantially spherical and so is the tube 310. The tube having a spherical shape can provide substantially homogeneous luminance in all directions. Alternatively, the twisted part 311 can be of elliptical or cylindrical shape.

Fig.4a depicts a schematic diagram of a tube arranged in a GLS A55 outer bulb in accordance with an embodiment of the present invention; Fig.4b is a cross-sectional view of the tube arranged in the GLS A55 outer bulb in Fig.4a.

As can be seen from Fig.4, when the tube 410 is substantially spherical, the available space inside a GLS A55 outer bulb 430 can be fully utilized for accommodating the tube 410. In comparison with the existing cylindrical or conoidal tube in Fig.2, the spherical tube 410 in Fig.3 utilizes more space inside the outer bulb 430, which can be ascribed to the fact that the arc length of the tube for light generation is longer, resulting in a higher luminous flux.

Fig.5a depicts a front view of a tube and a base of a discharge lamp in accordance with an embodiment of the present invention; Fig.5b depicts a top view of the tube and the base in Fig.5a; Fig.5c depicts a side view of the tube and the base in Fig.5a. Referring to Fig.5, the tube 510 comprises a first twisted part 511 having a first twist axis 1, and a second twisted part 512 having a second twist axis . The second twisted part 512 is communicatively connected with the first twisted part 511. The first twisted axis 1 and the second twisted axis 1 ' do not overlap but include a certain angle with one another. The two ends 513 of the tube 510 are formed so as to be connectable to a base 520 along a central axis 2 of the base 520. Moreover, when the tube 510 is connected to the base 520, each of the first twisted axis 1 and the second twisted axis 1 ' forms an angle with respect to the central axis 2 of the base 520. The angle can be in the range [45°, 90°]. As an example, the range is about 45° in Fig.5.

As shown in Fig.5, both the first twisted part 511 and the second twisted part 512 of the tube 510 are substantially of semi-spherical shape and are substantially symmetrical with respect to each other. Alternatively, the two twisted parts 511, 512 can be non-symmetrical or can even have different shapes. Each of the two twisted parts 51 1, 512 can be of cylindrical shape, conoidal shape, semi-spherical shape or a combination thereof.

Fig.6a depicts a perspective view of a tube and a base of a discharge lamp in accordance with an embodiment of the present invention; Fig.6b depicts a top view of the tube and the base in Fig.6a; Fig.6c depicts a side view of the tube and the base in Fig.6a.

Referring to Fig.6, the tube 610 comprises a first twisted part 611 having a first twist axis 1, and a second twisted part 612 having a second twist axis . The second twisted part 612 is communicatively connected with the first twisted part 611. The first twisted axis 1 and the second twisted axis 1 ' do not overlap but extend substantially parallel to each other. The two ends 613 of the tube 610 are formed so as to be connectable to a base 620 along a central axis 2 of the base 620. Moreover, when the tube 610 is connected to the base 620, each of the first twisted axis 1 and the second twisted axis 1 ' is substantially perpendicular to the central axis 2 of the base 620, and, in other words, forms an angle of about 90 ⁰ with respect to the central axis 2 of the base 620.

As shown in Fig.6, both the first twisted part 611 and the second twisted part 612 of the tube 610 are substantially of semi-spherical shape and are substantially symmetrical with respect to each other. Alternatively, the two twisted parts 611 , 612 can be non-symmetrical or can even have different shapes. Each of the two twisted parts 61 1, 612 can be of cylindrical shape, conoidal shape, semi-spherical shape or a combination thereof. Fig.7 depicts a flow chart of a method of producing a tube for a discharge lamp in accordance with an embodiment of the present invention.

Referring to Fig.7, the method 700 of producing a tube for a discharge lamp in accordance with an embodiment of the present invention comprises a step S710 of forming a twisted tube. The type and size of the twisted tube can vary according to the design and/or application requirements. Generally, the tube should be made of vacuum-tight material. Typically, the tube is made of glass. For example, tube T2 with an outer diameter of approximately 7mm can be used.

The step S710 comprises a substep S711 of twisting a first tube around a first twist axis into a predefined shape. Additionally, the step S710 can further comprise a substep S712 of twisting a second twist tube around a second twist axis into a predefined shape, and a substep S715 of communicatively interconnecting the twisted first tube and the twisted second tube so as to form the twisted tube.

The relative position of the first tube and the second tube can vary. In an embodiment, the first and second tubes can be interconnected in such a way that the first twist axis is in line with the second twist axis, i.e. that the first and the second twist axis overlap. For example, by interconnecting two identical, semi-spherical, twisted tubes, the twist axes of the two tubes overlapping one another, a spherical, twisted tube, as shown in Fig.3, can be formed. In another embodiment, the first and second tubes can be interconnected in such a way that the first twist axis and the second twist axis do not overlap. For example, the two twist axes can either include an angle with one another, as shown in Fig.5, or extend parallel to each other as shown in Fig.6.

Preferably, the first tube and the second tube are communicatively interconnected by means of front fusing in the case that the tubes are made of glass. In particular, the glass of the open front end of each of the first and the second tube is first melted, and then, the melted glass is fused to communicatively interconnect the two open ends. The melting and fusing processes are well-known glass processing operations, and therefore are not further discussed here.

In the case that the tube is used for a fluorescent lamp, the inner side of the tube should be coated with a fluorescent layer. To achieve such a fluorescent coating, the method 700 further comprises a step S713 of covering the inner side of each of the first tube and the second tube with fluorescent powder, and a step S714 of sintering the fluorescent powder. The steps S713 and S714 can be performed either before the substep S711 or after the substep S711. When the steps S713 and S714 are performed before the substep S711, i.e. the tube is first coated with a fluorescent layer and then twisted, the fluorescent layer could be destroyed, which would adversely affect the appearance and the performance of the fluorescent lamp. Therefore, the steps S713 and S714 are preferably performed after the substep S711, i.e the fluorescent coating is applied after the tube has been twisted.

Referring to Fig.7, the step S713 is preferably performed before the substep S715 under the following consideration. Typically, to cover the tube with fluorescent powder, the tube solution is first flushed through the tube and then the tube is suspended to allow excessive fluorescent solution to flow out of the tube, which is suitable for twisted tubes in shapes such as cylindrical, conoidal and semi-spherical. However, for some shapes of the twisted tube, such as a spherical shape as shown in Fig.3, it is difficult to cause excessive fluorescent solution to flow out of the tube by suspending the twisted tube. Thus, it would be advantageous to first perform the step S713, i.e. cover the inner side of two twisted tubes with fluorescent powder and then perform the substep S715, i.e. interconnecting the two twisted tubes to form a twisted tube of spherical shape. For example, in the case of a spherical, twisted tube made of two semi-spherical twisted tubes, it would be advantageous to first cover the inner side of the two twisted tubes of semi-spherical shape with fluorescent powder and then interconnect the two twisted tubes so as to form a twisted tube of spherical shape.

Furthermore, from a realizability point of view, the step S713 of sintering can be performed either before the interconnecting substep or after the interconnecting substep, but the latter is more efficient in process flow.

In an embodiment, the step S714 of sintering the fluorescent powder is performed before the interconnecting substep S715. As is well-known, the sintering procedure is performed at high temperature. Thus, the tube should be cooled before carrying out the interconnecting substep S715. According to standard procedures well known in glass processing, an annealing process is applied to the interconnected glass tubes such that the connection is resistant to cracking or shattering when subjected to a relatively small temperature change or mechanical shock. In the annealing process, the glass is heated until the temperature reaches a stress-relief point, that is, the annealing temperature. As a result, the tubes are first heated for sintering the fluorescent powder, then cooled for interconnecting them, and then heated again for the annealing process. In other words, the tubes are heated twice.

In another embodiment, the step S714 of sintering the fluorescent powder is performed after the interconnecting substep S715. Thus, the sintering procedure and the annealing process are two successive steps, and therefore, it is not necessary to heat the tubes twice, which makes the manufacturing process more efficient.

Further referring to Fig.7, the method 700 can also comprise a step S716 of deforming two ends of the twisted tube so as to be connectable to a base of the discharge lamp along a central axis (2) of the base, wherein an angle between the first twist axis (1) and the central axis (2) of the base is in the range [45°, 90°], as show in Figs.3, 5 and 6. When the twisted tube is formed by communicatively interconnecting two tubes, the step S716 can be performed either before or after the step S715. In some cases, it would be difficult to interconnect the two tubes in a desired manner without deforming the unconnected end of each tube. For example, in the absence of deformation, the unconnected end of one tube would collide with that of the other tube. Thus, in these cases, the step S716 is preferably performed before the step S715.

Figs.8a-f depict a procedure for producing a gas-filled tube with electrodes for a discharge lamp in accordance with an embodiment of the present invention. The tube in Fig.8 is substantially spherical and composed of two substantially semi-spherical tubes, but the procedure can also be used to produce tubes having different shapes. For example, two cylindrical, twisted tubes communicatively connected to each other can form one cylindrical twisted tube. For another example, the tubes in Fig.5 and Fig.6 can be formed by communicatively interconnecting two conoidal, twisted tubes with each other in different ways.

As shown in Fig.8a, first, two twisted tubes 811, 812 having a predefined shape are produced; next, the two twisted tubes 811, 812 are covered with fluorescent powder and a sintering process is applied to form the fluorescent layer; subsequently, two ends 81 11, 8112, 8121, 8122 of each of the two twisted tubes 811, 812 are cleaned to remove the fluorescent layer. Such operations can be implemented according to standard procedures in CFL manufacturing.

As shown in Fig.8b, an element 821, 822 equipped with an electrode is applied to a first end 8111 , 8121 of each of the two twisted tubes 811, 812. The electrodes are responsible for arc generation. Alternatively, in the case of an electrodeless lamp, the first end 8111, 8121 of each of the two twisted tubes 811, 812 is closed. Such operations can be carried out according to standard procedures in CFL manufacturing.

As shown in Fig.8c, mercury or amalgam can be inserted into one 822 of the two elements 821, 822 to enhance the efficiency of light generation, as is well-known in CFL manufacturing. Additionally, the corresponding element 822 into which the mercury or amalgam has been inserted is blanked off (?) or cut short, as shown in Fig.8c.

As shown in Fig.8d, a second end 8112 of the first twisted tube 811 and a second end 8122 of the second twisted tube 812 are communicatively interconnected by means of front fusing. Additionally, as is well-known in glass processing operations, an annealing procedure is applied to the connected twisted tube 810 such that the connection can be resistant to cracking or shattering when subjected to a relatively small temperature change or mechanical shock.

As shown in Fig.8e, the exchange of filling gases is performed according to standard procedures in CFL manufacturing. Additionally, the element 821 equipped with the electrode is blanked off (?) or cut short after the gas exchange, as shown in Fig.8f.

Finally, the manufactured gas-filled tube 810 with electrodes is shown in Fig.8f.

The order of the procedure for manufacturing the gas-filled tube as shown in Figs.8a-f can be changed. For example, the step of interconnecting the two twisted tubes in Fig.8d can be performed before the step of inserting electrodes in Fig.8b.

Additionally, the two ends of the tube 810 can be deformed so as to be connectable to a base of the discharge lamp along a central axis of the base, as described hereinabove. Such deformation can be performed before inserting the electrodes into the two ends 8111, 8121.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. The embodiments are illustrative rather than restrictive. It is intended that the invention include all modifications and variations to the illustrated and described embodiments within the scope and spirit of the invention. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim or in the description. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. In the device claims enumerating several units, several of these units can be embodied by one and the same item of hardware or software. The usage of the words first, second and third, et cetera, does not indicate any ordering. These words are to be interpreted as names.

Claims

CLAIMS:

1. A discharge lamp comprising:

a tube (310, 510, 610) comprising a first twisted part (311 , 511 , 61 1) which has a first twist axis (1); and

a base (320, 520, 620) having a central axis (2), the tube being connected to the base along the central axis (2);

wherein an angle between the first twist axis (1) and the central axis (2) of the base is in the range [45°, 90°].

2. The discharge lamp as claimed in claim 1, wherein the first twist axis (1) of the first twisted part (311 , 611) is substantially perpendicular to the central axis (2) of the base (320, 620).

3. The discharge lamp as claimed in claim 1 , wherein

the tube (510, 610) further comprises a second twisted part (512, 612) which has a second twist axis (1 ');

the first axis (1) and the second axis (1 ') do not overlap; and

the second twisted part (512, 612) of the tube is communicatively connected with the first twisted part ( 11, 611) of the tube.

4. A tube for a discharge lamp, comprising:

a first twisted part (310, 510, 610) which has a first twist axis (1); wherein

two ends (313, 513, 613) of the tube are connectable to a base (320,520, 620) of the discharge lamp along a central axis (2) of the base; and

an angle between the first twist axis (1) and the central axis (2) of the base is in the range [45°, 90°].

5. The tube as claimed in claim 4, wherein the first twist axis (1) of the first twisted part

(311, 611) is substantially perpendicular to the central axis (2) of the base (320, 620).

6. The tube as claimed in claim 4, further comprising:

a second twisted part (512, 612) which has a second twist axis (1 '); wherein the first axis (1) and the second axis (1 ') do not overlap; and

the second twisted part (512, 612) of the tube is communicatively connected with the first twisted part (511, 611) of the tube.

7. A method of manufacturing a tube for a discharge lamp, comprising the step of:

forming (S710) a twisted tube by twisting (S711) a first tube around a first twist axis

(i);

wherein two ends of the twisted tube are connectable to a base of the discharge lamp along a central axis (2) of the base, wherein an angle between the first twist axis (1) and the central axis (2) of the base is in the range [45°, 90°].

8. The method as claimed in claim 7, wherein the step of forming (S710) a twisted tube further comprises substeps of:

twisting (S712) a second tube around a second twist axis (1 '); and

communicatively interconnecting (S715) the first tube and the second tube to form the twisted tube.

9. The method as claimed in claim 8, wherein the first twist axis (1) is substantially aligned with the second twist axis ( ) after the first tube and the second tube have been interconnected.

10. The method as claimed in claim 8, wherein the first twist axis (1) and the second twist axis (1 ') do not overlap after the first tube and the second tube have been interconnected.

11. The method as claimed in claim 8, wherein

the first tube and the second tube are made of glass; and

an open end of the first tube and an open end of the second tube are communicatively interconnected by means of front fusing.

12. The method as claimed in claim 8, further comprising the following step before the interconnecting step:

covering (S713) the inner side of each of the first tube and the second tube with a fluorescent powder.

13. The method as claimed in claim 12, further comprising the following step after the interconnecting step:

sintering (S714) the fluorescent powder.

14. The method as claimed in claim 7, further comprising the step of deforming the two ends of the twisted tube so as to be connectable to a base of the discharge lamp along the central axis (2) of the base.

15. A method of manufacturing a discharge lamp, comprising the steps of:

manufacturing a tube according to any one of claims 7 to 13; and

connecting the tube to the base along the central axis (2) of the base.