LOW-PRESSURE MERCURY VAPOUR DISCHARGE LAMP

Abstract: Low-pressure mercury vapour discharge lamp having a discharge vessel (1) which is sealed in a gastight manner and is formed in such a way that the ends at which the electrodes (5,6) are located are juxtaposed, said ends being secured to a lamp cap (9) having a projecting wall part (11) provided with current connection pins (12,13) and accommodating a starter and possibly a capacitor, the end of the projecting wall part being closed by a cover (14).

Description: The invention relates to a low-pressure mercury vapour discharge lamp having a discharge vessel which is sealed in a gastight manner and is formed in such a way that the ends at which the electrodes are located are juxtaposed, said ends being secured to a lamp cap which is provided with a projecting wall part accommodating at least a starter, current connection pins being provided on either side of the projecting wall part. A lamp of this type is known from Dutch Patent Application NL-A- 8003277 laid open to public inspection. The lamp cap of the lamp described in said patent application mainly consists of a synthetic material and is formed to an integral unit. During the manufacture of such a lamp two juxtaposed electrode supply wires (one for each electrode) are first connected to the supply wires of a starter (and, if necessary, of a capacitor arranged parallel thereto), whereafater the lamp cap is connected to the discharge vessel (for example, by means of a suitable adhesive). The other supply wires of the electrodes are incorporated in the tubular current connection pins. It has been found that the operation of placing the assembly of the discharge vessel with starter and supply wires in the projecting wall part and the current connection pins, respectively, requires great precision and is time-consuming when the lamp cap is definitively secured to the discharge vessel. Such a complicated step is undesirable notably in a bulk-manufacturing process. It is the object of the invention to provide a lamp having a construction providing the possibility of simple manufacture in a bulk-manufacturing process. According to the invention a low-pressure mercury vapour discharge lamp of the type described in the opening paragraph is therefore characterized in that the end of the projecting wall part is closed by a cover. Due to the construction of the lamp cap, the lamp according to the invention can be manufactured in a simple and reliable way in a bulk-manufacturing process. Unlike the lamp cap of the known lamp, the end of the projecting wall part is not closed by the cover until all other operations on the lamp cap have been completed. During manufacture the lamp cap (with the projecting cylindrically shaped wall part which is not yet closed) is first secured to the discharge vessel. Then the starter and the anti-interference capacitor are introduced through this said, still open wall part, their supply wires are connected to electrode supply wires and finally the opening is closed by the cover. In a preferred embodiment of the lamp according to the invention the inside of the projecting wall part is provided with two oppositely located guide walls, each defining with said projecting wall part a space which is tapered in the direction of the cover and in which a respective supply wire of each electrode is incorporated, which supply wires are connected at least to the supply wires of the starter in the proximity of the cover. This construction facilitates the connection of the supply wires for the electrodes to those of the starter and the capacitor. The said electrode supply wires are inserted through the narrowing guide walls and positioned near the end. This is very advantageous in a bulk-manufacturing process. The closure of the projecting wall part by means of the cover is preferably effected by welding or by means of a snap-connection. The invention will be described in greater detail with reference to the accompanying drawings in which Figure 1 shows an embodiment of a low-pressure mercury vapour discharge lamp according to the invention; Figure 2 diagrammatically shows three steps in a process of manufacturing the lamp of Figure 1, and Figure 3 is a cross-section of the lamp cap of a lamp according to the invention in which the discharge vessel comprises four interconnected tubular parts placed in a square. The low-pressure mercury vapour discharge lamp of Figure 1 has a discharge vessel 1 (filled with mercury and a rare gas) which is sealed in a gastight manner and which comprises two parallel juxtaposed discharge tubes (2,3) which are connected together near their closed ends by means of the cross-section 4. The electrodes 5 and 6 between which a U-shaped discharge is maintained during operation of the lamp are provided at the other ends of the tubes 2 and 3. A luminescent layer 7 which converts the radiation generated in the discharge into visible light is present on the inner wall of the discharge vessel. An oval shaped wall part 8 (for example, consisting of aluminium) of the lamp cap 9 is secured by means of an adhesive (such as cement) to the ends of the discharge vessel at which the electrodes are located. A synthetic material part 10 is secured to the oval part 8 by means of a riveted connection. This part 10 is provided with a cylindrically shaped wall part 11 in cross-section rectangular projecting in the axial direction and accommodating a glow starter and a capacitor (not visible in Figure 1). This cylindrically shaped part has a rectangular cross-section. Current connection pins 12 and 13 are present on either side of part 11. The end of part 11 is closed by a synthetic material cover 14, for example by means of a snap-connection. Figure 2 shows diagrammatically a number of steps in the manufacturing process of the lamp from which it is apparent that the construction according to the invention has clear advantages. In the manufacture of the lamp and lamp cap with the still open part 11 is first secured to the discharge vessel, whereafter the starter and the capacitor are provided and the part 11 is closed by the cover 14. Figure 2a shows a first process step. The oval aluminium part 8 is already secured to the discharge vessel. The still open lamp cap 10 is subsequently provided by moving it over the parallel projecting supply wires 15, 16, 17 and 18. The supply wires 15 and 18 are thereby incorporated in the cylindrically shaped current connection pins 12 and 13, whilst the wires 16 and 17 (a supply wire for different electrodes) are incorporated in two funnel-shaped quide walls 19 and 20 facing each other on the inner side of the cap. A guiding lead-in space is then formed for the said wires. The walls 19 and 20 substantially face each other (see also Figure 3). Upon further connection of 10 to 8, the wires 16 and 17 extend as far as the end of the lamp cap (see Figure 2b showing the situation in which the parts 8 and 10 are connected together). Subsequently the starter 21 and the capacitor 22 (whose supply wires extend in the same direction as the supply wires 16 and 17 of the electrodes) are inserted into part 11 via the still open end and are connected to the supply wires 16 and 17 (for example, by means of soldering). Subsequently part 11 is closed by cover 14. This is shown in Figure 2c. Due to the presence of a discharge vessel having four tubular parts placed in a square, the synthetic material cap 11 in Figure 3 has a square shape in the cross-section. The walls 19 and 20 for guiding the supply wires are visible. The openings 23 and 24 at the constricted ends of the walls 19 and 20 are large enough to allow the ends of the wires 16 to 17 to pass. Furthermore the starter 21 is shown by means of a broken line. In a practical embodiment of the lamp according to Figure 1 the length of the tubular parts is approximately 13 cm, the internal diameter is 10 mm. For a rare-gas filling of argon (399.966Pa - 3 torr) the light output was approximately 600 lumen at a power supply to the lamp of approximately 9 W.

Claims: A low-pressure mercury vapour discharge lamp having a discharge vessel (1) which is sealed in a gastight manner and is formed in such a way that the ends at which the electrodes are located are juxtaposed, said ends being secured to a lamp cap (9) which is provided with a projecting wall part (11) accommodating at least a starter (21), current connection pins (12, 13) being provided on either side of the projecting wall part, characterized in that the end of the projecting wall part is closed by a cover (14). A low-pressure mercury vapour discharge lamp as claimed in Claim 1, characterized in that the inside of the projecting wall part is provided with two oppositely located guide walls (19, 20), each defining with said projecting wall part a space which is tapered in the direction of the cover and in which a respective supply wire (16, 17)of each electrode is incorporated, which supply wires are connected at least to the supply wires of the starter in the proximity of the cover.

Inventors: REEMERS, HERMAN ANTON J., RIDDERS, JOHANNES ANTONIUS M.
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1987
Main classification: H01J5
IPC codes: H01J5, H01J61