GB2176648A

GB2176648A - Low-pressure mercury vapour discharge lamp

Info

Publication number: GB2176648A
Application number: GB08611068A
Authority: GB
Inventors: Johannes Rudolf Gelens
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1985-05-10
Filing date: 1986-05-07
Publication date: 1986-12-31
Also published as: BE904735A; GB8611068D0; NL8501340A; FR2587542A1; DE3613881A1; GB2176648B; JPS61260542A

Abstract

In a low-pressure mercury vapour discharge lamp comprising a tubular discharge vessel (2) which is sealed in a gas-tight manner and is filled with mercury and a rare gas, the discharge vessel comprises at least three tube portions (5, 6, 7) which are interconnected by means of coupling joints (8, 9) and are bent into the shape of a U, the coupling joints (8, 9) being formed by fusing together collars facing each other and arranged to surround openings in the walls of two adjacent U-shaped tube portions located near the ends of the limbs. As shown the U-tubes are of similar dimensions, however the radius of curvature of the two outer U-tubes 5, 7 may be smaller than the middle U-tube 6, though symmetrically disposed with respect thereto. <IMAGE>

Description

SPECIFICATION Low-pressure mercury vapour discharge lamp The invention relates to a low-pressure mercury vapour discharge lamp provided with a tubular glass discharge vessel which is sealed in a gas-tight manner, which is filled with mercury and a rare gas and at the ends of which electrodes are arranged between which a discharge is maintained during operation of the lamp, this discharge vessel comprising at least three interconnected tube portions which are bent into the shape of a U, which are arranged parallel to and beside each other and whose limbs are orientated in the same direction, these tube portions being traversed by the discharge during operation of the lamp.

Such a lamp is known from Japanese published Patent Application No. 59-119669.

This lamp comprises a lamp envelope which surrounds the discharge vessel which is connected to an Edison lamp cap so that the lamp is suitable to be screwed into fittings for incandescent lamps. The lamp is an alternative to an incandescent lamp for general illumination purposes.

The connection between the various tube portions of the discharge vessel of the known lamp bent into the shape of a U is established by means of specifically formed chambers, whose walls accommodate the ends of the said tube portions in a gas-tight manner. The chambers are interconnected in such a manner that the discharge path extends from a first electrode via a U-shaped tube portion and a chamber to the second U-shaped tube portion and so on to the second electrode in the third U-shaped tube portion. The use of such chambers for establishing the connections between the separate tube portions is complicated and involves a time-consuming procedure during the manufacture of the lamp. The lamp envelope surrounding the discharge vessel is then necessarily voluminous.Due to the presence of the chambers, the lamp moreover is comparatively long, which limits the possibilities of application in given luminaires.

The invention has for its object to provide a compact low-pressure mercury vapour discharge lamp having a high light output, which does not suffer from the aforementioned limitations.

According to the invention, this object is acheived with a low-pressure mercury vapour discharge lamp of the kind mentioned in the opening paragraph in that the U-shaped tube portions are interconnected by coupling joints formed by fusing together collars facing each other and arranged to surround openings in the walls of two adjacent U-shaped tube portions located in the proximity of the ends of the limbs.

The lamp according to the invention is very compact and has a high efficiency.

By the use of the said coupling joints, the U-shaped tube portions can be arranged very close to each other, a very compact lamp then being obtained. As compared with the known lamp, the lamp further has a very homogeneous brightness. The said coupling joints can be formed rapidly and in a reliable manner. The time-consuming step during the manufacture in which the specifically formed chambers are used in avoided.

In an embodiment, the U-shaped tube portions are substantially identical to each other and are consecutively arranged. The longitudinal axes of the limbs of the U-shaped tube portions are then located in two planes, which are substantially at right angles to the plane passing through the longitudinal axes of the two limbs of one of the U-shaped tube portions. This embodiment has the advantage that a sufficient amount of space is present between the limbs of the tube portions for accommodating an electrical stabilization ballast. Such a lamp is not only very compact, but can also be advantageously manufactured.

In fact, only one type of U-shaped tube portion need to be manufactured.

In another embodiment of the lamp according to the invention, the distance between the respective limbs and radius of curvature of the bent part of each of the two outer tube portions is smaller than that of the intermediate central tube portion, the tube portions located on the outer side being slightly offset towards the intermediate tube portion, said tube portions arranged with respect to each other such that their respective planes of symmetry coincide.

Such a lamp has a very homogeneous light distribution. The discharge vessel can be enclosed by an envelope having comparatively small dimensions.

A low pressure mercury vapour discharge lamp in accordance with the invention will be described, by way of example, with reference to the accompanying drawing.

In the drawing, Figure 1 shows in elevation a low-pressure mercury vapour discharge lamp, according to the invention, and Figure 2 shows in side elevation the discharge vessel of the lamp shown in Fig. 1.

The lamp shown in Fig. 1 comprises a glass cylindrical envelope 1, which is sealed slightly spherically at one end and is provided with a refraction profile in order to obtain a light distribution as homogeneous as possible. Inside this envelope there is arranged a tubular dis charge vessel 2, which is sealed in a gas-tight manner, which is filled with mercury and a rare gas and on the inner wall of which a layer of luminescent material is present which converts the ultraviolet radiation produced in the discharge into visible light. At the ends of the discharge vessel there are arranged elec trodes 3 and, (cf. Fig. 2) between which a discharge is maintained during operation.The discharge vessel comprises three tube portions 5, 6, 7 interconnected in series which are bent into the shape of a U and are consecutively arranged, the longitudinal axes of the limbs of these tube portions being located in two parallel extending planes which are at right angles to a plane passing through the limbs of one U-shaped tube portion (for example 5).

As shown in Fig. 2, the U-shaped tube portions are interconnected by coupling joints located in proximity to the ends of the respective limbs. The coupling joint between the tube portions 5 and 6 is designated by reference numeral 8 and that between the portions 6 and 7 is designated by reference numeral 9.

During the manufacure of a number of these lamps, first straight tube portions are provided on the inner side with a luminescent layer.

Subsequently, one end of some of the tube portions is provided with a mount (which carries an electrode and in which an exhaust tube is present). The other end of each of these tube portions is sealed in a gas-tight manner, after which the said tube portions are bent into the shape of a U. Thus, the tube portions 5 and 7 are obtained. Other tube portions are sealed at one end by means of a mount which is provided simply with an exhaust tube (and is not provided with an electrode). The other end is sealed in a gas-tight manner, after which these tube portions are also bent into the shape of a U. Thus, the tube portion 6 is obtained.

The limbs of the portions 5 and 6 are then arranged beside each other, after which a coupling joint (such as 8) is formed between the electrode-free limb of the tube portion 5 and the adjacent limb of the tube portion 6. This is effected by locally softening a wall region at the respective limbs by heating and then blowing air into the tube portions through their exhaust tubes so as to form an opening at that region surrounded by an outwardly directed collar of glass. Subsequently, the collars of the adjacent limbs are fused together in a gas-tight manner to form the coupling joint. In a similar manner, the tube portions 6 and 7 are interconnected by the coupling joint 9 comprising fused collars formed on adjacent limbs. After the discharge envelope has been exhausted, the exhaust tubes are sealed and the mercury is metered (for example by opening a capsule in the discharge vessel).The sealed exhaust tube in the tube portion 6 forms an appendix 13, by means of which the mercury vapour pressure in the discharge vessel during operation of the lamp can be stabilized on an optimum value. The control of the vapour pressure can be further improved in that an amalgam(14) consisting, for example, of indium, bismuth and mercury is provided in the appendix. The discharge vessel thus formed is secured on a base plate and is surrounded by a cylindrical lamp envelope (1).

The discharge in the discharge vessel passes during operation from the electrode 3 through the tube portion 5 to the coupling joint 8, which is located near the end of the electrode-free limb of the tube portion 5. Subsequently, the discharge traverses the intermediate tube portion 6 completely to the coupling joint 9, at which the discharge enters the electrode-free limb of the tube portion 7. The discharge then traverses the said tube portion 7 to the electrode 4.

The lamp shown in Fig. 1 further comprises an electrical stabilization ballast 10, which is arranged between the limbs of the said Ushaped tube portions 5, and 7. To the envelope 1 is secured a conical lamp bowl 11 of synthetic material, which carries an Edison lamp cap 12, by means of which the lamp can be screwed into a fitting used for incandescent lamps. Further, the space formed by the lamp bowl 11 accommodates a starter (not shown in the drawing).

In a practical embodiment, the lamp described above has a power of 13 W (inclusive of ballast). The length of each U-shaped tube portion is about 130 mm. The inner diameter of the said tube portions is about 10 mm.

The overall length of the discharge path between the electrodes 3 and 4 is about 370 mm. The light output of the lamp is about 600 Im. The inner diameter of the cylindrical envelope is about 62 mm. The discharge vessel contained besides a small quantity of mercury also argon at a pressure of 3 torr. The luminescent material consisted of a mixture of two phosphors, i.e. green luminescing terbium-activated cerium magnesium aluminate and red luminescing yttrium oxide activated by trivalent europium.

Claims

1. A low-pressure mercury vapour discharge lamp provided with a tubular discharge vessel which is sealed in a gas-tight manner, which is filled with mercury and a rare gas and at the ends of which electrodes are arranged between which during operation of the lamp a discharge is maintained, this discharge vessel comprising at least three interconnected tube portions which are bent into the shape of a U, which are arranged parallel to and beside each other and whose limbs are orientated in the same direction, these portions being traversed by the discharge during operation of the lamp, characterized in that the U-shaped tube portions are interconnected by coupling joints, which are formed by fusing together collars facing each other and arranged to surround openings in the walls of two adjacent U-shaped tube portions located in the proximity of the ends of the limbs.

2. A low-pressure mercury vapour discharge lamp as claimed in Claim 1, characterized in that the U-shaped tube portions are substantially indentical to each other and are consecutively arranged.

3. A low-pressure mercury vapour discharge lamp as claimed in Claim 1, characterized in that the distance between the respective limbs and the radius of curvature of the curved part of each of the two outer tube portions is smaller than that of an intermediate tube portion, the tube portions located on the outer side being slightly offset towards the intermediate tube portion, said tube portions being arranged with respect to each other such that their respective planes of symmetry coincide.

4. A low-pressure mercury vapour discharge lamp as claimed in Claim 1, 2 or 3, characterized in that a U-shaped tube portion free of electrodes is provided at one end with an appendix.

5. A low-pressure mercury vapour discharge lamp as claimed in Claim 4, characterized in that an amalgam is present in the appendix.

6. A low-pressure mercury vapour discharge lamp substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.