IE41998B1 - Improvements in or relating to discharge-type projection lamps - Google Patents

Abstract

1517451 Discharge lamps COMPAGNIE DES LAMPES 14 Jan 1976 [15 Jan 1975] 01307/76 Heading H1D In a discharge type projection lamp with an envelope 1 housing electrodes 4, 5 at opposite ends and enclosing a light-transmitting tube 6 whose open ends are sealed to the envelope 1, a core member 7 having a helical channel in its outer periphery is secured within the tube 6 to co-operate therewith to define a helical discharge chamber between the electrodes 4, 5. The envelope 1 may be coated internally with a fluorescent or luminescent substance and externally with a laquer, varnish or silicate compound to modify the colour of the emitted light. Both the envelope 1 and tube 6 may be made of hard glass, silica, quartz or plastics, and the core 7 may be moulded of similar material, or it may be formed as a composite of adjacent elements.

Description

The present invention relates to a discharge-type projection lamp.

Discharge-type projection lamps generally include a cover having a pair of electrodes therein between 5 which a discharge takes place in use. It is often desirable to reduce the overall length of the lamp by arranging for the discharge to take place along a tortuous path, for example a helical path. In existing lamps, the helical path is often created by forming the cover itself into a helical shape. This is disadvantageous since lamps of this type are not all made in exactly the same manner, and their individual electrical and photometric properties can be widely different.

It is an object of the present invention to obviate or mitigate this disadvantage.

According to the present invention, there is provided a discharge-type projection lamp comprising a closed, fluid-tight cover made of light-transmitting material, a pair of spaced electrodes disposed within the cover at either end thereof, between which electrodes a discharge takes place in use, a light transmitting tube within the cover, the ends of the tube being open and being welded to the internal surface of the cover 2b so as to create a fluid-tight seal therebetween, and a core member having a generally helical channel in its outer periphery, the core member being secured within the tube between the electrodes and co-operating with the internal surface of the tube to define a generally helical chamber, the core member and tube -241998 being arranged so as to prevent said discharge from taking place otherwise than along the generally helical chamber..

The degree of precision which can be achieved on the one hand in the manufacture of the tube and the core member and on the other hand in the positioning of the core member between the electrodes is such that, for a given gas filling and power rating, the same electrical and photometric properties can be obtained from one lamp to another. In addition, light emission from the discharge in the helical chamber can reach that giving maximum luminous efficiency.

A discharge-type projection lamp according to the invention and having a verylow power rating (0.1 to 10W) for operation under a 50 to 600 V a.c. or d.c. supply can be manufactured economically. It is also possible to produce a discharge-type projection lamp according to the invention which has a power rating of 10 to 100W and which is to be operated at voltages of 600 to 5000 V.

The lamp of the present invention can be filled with a rare gas or mixture of rare gases. One or more volatile metals or volatile metal compounds which produce a coloured discharge can be added. The interior surface of the cover can be coated with a fluorescent or luminescent substance, and its exterior surface can be coated with a suitable laquer, varnish or silicate compound, when it is desired to modify the colour of the light emitted by the lamp or cause the light colouration to be diffused by obliterating part of its spectrum or by effecting primary excitation of the fluorescent or luminescent substance. -341998 An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is an axial sectional view of a dischargetype projection lamp according to the present invention; and Figure 2is a side view of a core member forming part of the lamp of Figure 1.

Referring to the drawing, the discharge-type projection lamp shown therein comprises an external cover 1 which is closed and fluid-tight. The cover is made of light transmitting material, such as hard glass, ordinary glass, quartz, plastics or transparent or translucent silica. Electrical leads 2 and 3 are embedded in the ends of the cover 1, the leads 2 and 3 being respectively connected to electrodes 4 and 5 disposed within and at either end of the cover.

Within the cover 1 is an open-ended tube 6 which is also made of light-transmitting material, such as hard glass, transparent silica, quartz or plastics.

The ends of the tube 6 are welded to the internal surface of the cover 1 so as to create a fluid-tight seal therebetween.

Disposed within the tube 5 and between the electrodes and 5 is a helical core member 7, in the form of a section of worm screw (shown in detail in Figure 2).

The core member 7 is welded or otherwise mechanically secured in a sealing manner to the internal surface of the tube 6. The core member 7 has a helical groove in its external surface, and co-operates with the internal surface of the tube 6 to define a helical chamber. The tube 6 and the core member 7 are so arranged as to prevent a discharge from taking place between the -4419 9 8 electrodes 4 and 5 otherwise than along the helical chamber. The core member 7 is preferably made of hard glass, transparent silica or plastics, and is advantageously produced by a moulding process.

In an alternative embodiment (not shown) the core member is composite and comprises a plurality of elements disposed one after the other in longitudinal direction of the lamp, each element having a longitudinally extending groove therein. The groove in each element is angularly displaced with respect to the groove in each adjacent element, and communicates therewith so that the grooves together define a generally helical channel in the external surface of the core member.

In the embodiment described above in relation to Figures 1 and 2, the channel in the core member has a rectangular cross-sectional profile. However, in order to improve the luminous efficiency of the discharge lamp, the channel can have a cross-sectional profile which is other than rectangular, for example trapezoidal, and also that part of the core member which separates adjacent flights of the channel can be made as thin as possible in order to increase the volume of the helical discharge member.

Claims (5)

1. WHAT WE CLAIM IS:1. A discharge-type projection lamp comprising a closed, fluid-tight cover made of light-transmitting material, a pair of spaced electrodes disposed within the cover at either end thereof, between which electrodes a discharge takes place in use, a light-transmitting tube within the cover, the ends of the tube being open and being welded to the internal surface of the cover so as to create a fluid-tight seal therebetween, and a core member having a generally helical channel in its outer periphery, the core member being secured within the tube between the electrodes and co-operating with the internal surface of the tube to define a generally helical chamber, the core member and tube being arranged so as to orevent said discharge from taking place otherwise than along the generally helical chamber.

2. A projection lamp as claimed in claim 1 wherein the core member is produced by a moulding process.

3. A projection lamp as claimed in claim 1 or claim 2 wherein the core member is mechanically secured in a sealing manner within said tube.

4. A projection lamp as claimed in claim 1,2 or 3 wherein the tube and the core member are made of hard glass, transparent silica or plastics and the cover is made of hard glass, ordinary glass or transparent or translucent silica.

5. A discharge-type projection lamp substantially as hereinbefore described with reference to the accompanying drawing.