GB2079528A

GB2079528A - A sodium vapor discharge lamp

Info

Publication number: GB2079528A
Application number: GB8117309A
Authority: GB
Original assignee: Patent Treuhand Gesellschaft fuer Elektrische Gluehlampen mbH
Current assignee: Osram GmbH
Priority date: 1980-07-02
Filing date: 1981-06-05
Publication date: 1982-01-20
Also published as: GB2079528B; DE8017792U1

Abstract

In a sodium vapor discharge lamp with an arc tube 1 mounted on a support frame 6 inside a tubular outer jacket 2, the jacket 2 comprises a filtering material and/ or a filter coating, the spectral transmissivity of which is selected so that only radiation from the sodium D lines (589 nm) is emitted by the lamp. One end of the jacket 2 has a base, comprising a glass disc 8 with contact pins 9 and the other end is closed by a plastics plug 10. The lead-in wires for the electrodes 4, 5 are preferably curved in hook shape. The outer jacket need not be sealed and thus may have an opening 13 to the exterior. The lamp may be used in dark room lighting. <IMAGE>

Description

SPECIFICATION Sodium vapour discharge lamp The present invention relates to a sodium vapor discharge lamp, especially for use in dark room lighting and comprising an arc tube and a radiation transmissive outer jacket surrounding the arc tube.

The spectral sensitivity of colour photographic papers has a very distinct minimum in the region from 570 to 610 nm. For dark room lighting, therefore, sodium vapor discharge lamps are particularly suitable as the line spectrum emitted by the lamps has, apart from the relatively intense double lines at 589 nm, only few secondary lines in the blue and red region. In spite of the favourable radiation spectrum of the sodium vapor discharge lamps, appropriate filtering measures have to be taken to prevent the radiation of the secondary lines which would otherwise cause chemical fog on the sensitive colour photographic papers.

Known filtering measures in such dark room lighting consist of relatively complex filtering devices which are part of the light. Sodium spectroscopic lamps having a sealed evacuated tubular outer envelope are used as the light source in such dark room lighting. Inside the outer envelope, a so-called arc tube is supported on a mounting frame. The arc tube comprises a discharge envelope with sealed-in electrodes and an appropriate filling, such as sodium and a rare gas. Lamps of this type are provided with a base, e.g. a Pico-9-base. The outer envelope is sealed at the base end by a sealed-in pressed glass disc comprising contact pins, whereas the end remote from the base is provided with an evacuating tip. The outer envelope used in these prior art spectroscopic lamps is radiation transmissive at least in the entire visible region of the spectrum.

It is an object of the invention to provide a sodium vapor discharge lamp especially suited to dark room lighting and of simplified construction. It is also an object of the invention to provide a lamp of small dimensions requiring only a shallow mounting depth in a lighting fitting.

According to the present invention there is provided a sodium vapor discharge lamp comprising an arc tube supported by a radiation transmissive outer jacket surrounding the said arc tube, one end of the outer jacket being closed by a base wherein the outer jacket is of a filter material and/or has a coating of filter material of which the spectral transmissivity is such that only radiation of the sodium-D-lines at 589 nm is emitted by the lamp.

With the outer jacket of the lamp being designed as a filter tube, no further filtering arrangements in the lamp or a lighting fitting are required, and a more simplified construc tion may be obtained.

In the lamp of the invention the outer jacket provided as a filter need not be hermetically sealed. One end of the outer jacket is closed by the base, whereas the other end has, as closing means, a plug inserted into the tube.

The plug preferably consists of a disc having a collar-like extension. The latter is inserted into the jacket, the collar abutting the inner wall thereof, with the disc covering the end of the outer jacket from the exterior over the entire cross section. The plug is preferably made of plastics material, and is for example, glued into the tube. It may have an opening permit ting the entrance of air into the outer jacket.

The base which closes the outer jacket consists preferably of a pressed glass disc carrying contact pins. The said disc is inserted into the end of the outer jacket and is, for instance, glued to the said outer jacket, which may be tubular. The contact pins are sealed in the disc. The base is profitably of the Pico-9 standard. In order to bring about a reduction of the size of the lamp in the longitudinal axis, the lead-in wires for the electrodes are bent to hook shape in the interior of the arc tube. The free ends of the lead-in wires are bent to include an approximately at right angle to the longitudinal axis of the arc tube and are welded crosswise to the electrode pins in the axis. The arc tube ends are pinched round the lead-in wires to seal the latter.

The tube is supported without any interme diate member directly by the lead-in wires which project outwardly from the arc tube ends. One of the lead-in wires (at the end remote from the base) is welded to the mount ing frame, whereas the other lead-in wire (at the base end) is welded to one of the contact pins. The mounting frame, in turn, is affixed to one of the contact pins. To provide support for the mounting frame in the outer jacket, the mounting frame has a brace member which abuts the inner wall of the outer jacket.

As no intermediate supporting members are required, the mounting frame may be of short ened construction.

A preferred embodiment of the present in vention will now be described by way of example only with reference to the accompa nying drawings of which; Figure 1 shows a side view of a lamp in accordance with the present invention having an outer jacket; Figure 2a shows a side view of the lamp of Fig. 1 without the outer jacket, and Figure 2b shows a side view of the lamp of Fig. 2a turned through 90 .

Fig. 1 illustrates a sodium vapor discharge lamp wherein an arc tube 1 is encompassed by a tubular outer jacket 2. The arc tube 1 comprises a discharge vessel 3 having elec trodes 4, 5 sealed in its ends, and a filling of sodium and rare gas contained therein. The arc tube 1 is supported by a mounting frame 6. The latter has a brace member 7 which abuts the inner wall of the outer jacket 2. The tubular outer jacket 2 is of a filter material which is not transmissive for radiation of certain wavelength ranges and may have an interference coating completing the filtering effect and applied preferably to its external surface. Instead of or as well as being of a filter material, the outer jacket may be provided with a filter coating.The filter material and/or the filter coating are so selected and matched to one another that only radiation of the sodium-D-lines at 589 nm is transmitted by the outer jacket 2 and thus emitted by the lamp. The interfering secondary lines of the sodium spectrum in the blue and red regions are suppressed by the outer jacket 2 which is provided as the filtering tube.

The outer jacket 2 has at its lower end a Pico-9-base. The latter consists of a pressed glass disc 8 in which are sealed the contact pins 9. The pressed glass disc 8 is glued into the tubular outer jacket 2. A plastics plug 10 is inserted in the upper end of the outer jacket 2 and glued to the said outer jacket 2. The plug 10 consists of a disc 11 having a collarlike extension 1 2 which abuts the inner wall of the jacket 2. Extension 12 is preferably conical. The plug 10 has in its disc-shaped portion 11 an opening 1 3 permitting extrance of air into the outer jacket 2.

From Figs. 2a and 2b can be seen that the arc tube 1 is supported directly by the lead-in wires 14, 1 5 sealed into the arc tube ends.

The upper U-shaped lead-in wire 1 5 is welded to the mounting frame 6; the lower U-shaped lead-in wire 14 is welded to one of the contact pins 9 passing into the outer jacket.

The lateral lead-in wire support rod 1 6 of the mounting frame 6 is also affixed, by resistance welding, to two of the contact pins 9 passing into the outer jacket 2.

The arc tube arrangement turned through 90 and shown in Fig. 2b also shows the connection between the portions of the lead-in wires 14, 1 5 and the respective electrodes 4, 5 in the discharge vessel 3. The free ends of the lead-in wires 14, 1 5 are bent to a hook shape. The pins of the electrodes 4, 5 lying in the longitudinal axis of the arc tube are welded crosswise to the hook-shaped lead-in wires 14, 1 5. The ends of the arc tube 1 are pinched round the lead-in wires 14, 1 5.

The lamp illustrated in the Figures has, for instance, a power input of 10 W. The outer jacket is about 70 mm long and 20 mm in diameter. Ignition of the lamp is effected by a commercially available starter, and a commercially available choke may be used for stabilizing the lamp in operation.

Claims

1. A sodium vapor discharge lamp comprising an arc tube supported by a radiation transmissive outer jacket surrounding the said arc tube, one end of the outer jacket being closed by a base wherein the outer jacket is of a filter material and/or has a coating of filter material of which the spectral transmissivity is such that only radiation of the sodium-D-lines at 589 nm is emitted by the lamp.

2. A sodium vapor discharge lamp as claimed in claim 1, wherein the outer jacket is tubular and end of the outer jacket remote from the base is closed by a plug.

3. A sodium vapor discharge lamp as claimed in claim 2 wherein the plug comprises a disc with a conical collar fitted thereto, the disc covering the end of the tubular outer jacket and the collar abutting the inner wall of the outer jacket.

4. A sodium vapor discharge lamp as claimed in claim 2 or 3 wherein the plug is of plastics material.

5. A sodium vapor discharge lamp as claimed in any of claims 2 to 4 wherein the plug is provided with an opening permitting the entrance of air into the outer jacket.

6. A sodium vapor discharge lamp as claimed in any of claims 1 to 5, wherein the base consists of a glass disc having contact pins sealed therein which are passed to the exterior of the said outer jacket.

7. A sodium vapor discharge lamp as claimed in claim 6 wherein the glass disc is inserted in the end of the outer jacket and is glued to the outer jacket.

8. A sodium vapor discharge lamp as claimed in any of claims 1 to 7 having lead-in wires for the electrodes of the arc tube wherein the lead-pin wires are sealed in the arc tube ends and are bent to hook shape in the interior of the arc tube, and the free ends of the lead-in wires are bent approximately at right angles to the arc tube axis and are welded crosswise to the electrodes lying in the axis.

9. A sodium vapor discharge lamp as claimed in any of claims 1 to 8, wherein the arc tube is supported within the outer jacket on a mounting frame (6) (at the end remote from the base) directly via the lead-in wires (14, 1 5) sealed in the arc tube ends and at a contact pin (9) of the base (at the end adjacent the base), respectively.

10. A sodium vapor discharge lamp as claimed in claim 9 wherein the arc tube is supported on the frame at its end adjacent the base, via a contact pin of the base and, at its end remote from the base directly by a lead-in wire sealed in the end of the arc tube.

11. A sodium vapor discharge lamp substantially as herein described with reference to; the accompanying drawings.