AU775446B2 - A mercury-free luminescent/flourescent lamp with cold hollow cathodes for colored decorative lighting or illuminated signs - Google Patents

Description

P/00/011 28/5/91 Regulation 32(2)

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: A MERCURY-FREE LUMINESCENT/FLUORESCENT LAMP WITH COLD HOLLOW CATHODES FOR COLORED DECORATIVE LIGHTING OR ILLUMINATED SIGNS The following statement is a full description of this invention, including the best method of performing it known to us

SPECIFICATION

A mercury-free luminescent/fluorescent lamp with cold hollow cathodes for colored decorative lighting or illuminated signs The invention relates to luminescent/fluorescent cold hollow cathode lamps, in particular for decorative colored lighting and illuminated signs.

Such lamps are made in a glass tubular hollow body whose interior is covered with a fluorescent powder. The tube coated with powder in this way is sealed at both ends by electrodes and filled with a pure rare gas or a mixture of rare gases. Mercury is also added.

These electrodes function as emissive cathodes during evry other half-cycle of an alternating current supply and passively as anodes during the other halfcycle.

They are referred to as "cold hollow cathodes" or o oo "cold emissive hollow cathodes" because the emission of electrons by the cathodes is principally obtained by S 20 secondary emission due to ionic impact, with thermionic emission having a marginal role.

These cold cathodes generally include an activated metal cylinder.

Accordingly, following an electrical discharge in the gaseous medium of the tube, between the two electrodes, the mercury vapor emits invisible UV radiation that is converted into visible radiation by the *...fluorescent powder.

~Mercury is a toxic product, however, hazardous for man and for the environment. Also, it generates light pollution phenomena that have been condemned by amateur astronomers and persons seeking to protect rare winged species and irisecLs. Furthermore, it also causes shadow areas in the tube during cold periods.

The invention aims in particular to alleviate these 2 drawbacks.

To this end, it proposes a mercury-free lamp with activated cold hollow cathodes, including a glass tubular hollow body whose interior is covered with a fluorescent powder, which has at its two ends activated cold hollow cathode electrodes and which is filled with a mixture of rare gases, wherein the mixture of rare gases includes to 99% neon and up to 1% of a blocking or complement rare gas or mixture of rare gases, the remainder being xenon, and the activated cold hollow cathodes have an active layer including barium fluoride or a compound containing an element from group III B of the periodic table of the elements.

Thanks to these features, a tubular lamp or discharge tube is obtained enabling fluorescence to be achieved without the specific UV radiation from mercury.

Fluorescence is achieved by ultra violet and far ultra violet radiation generated by the neon-xenon mixture.

The service life of this kind of tube is greater than that of a mercury tube because there is no amalgam to stain the fluorescent powder because there is no mercury. The absence of mercury also allows operation at an ambient temperature of approximately -30°C and with a very regular voltage lower than that of a conventional 25 mercury tube. In practice, the voltage saving is more than Also, the colors obtained are very saturated and *provide excellent contrast.

~The element from group III B of the periodic table of the elements is preferably selected from scandium, yttrium ana lanthanum, i.e. a lanthanide, scandium and yttrium beinc attached to the lanthanide family.

The ccrresponding preferred compounds are chosen from the group comprising lanthanum oxide (La 2 03), lanthanum hexaboride (LaB 6 scandium oxide (Sc 2 03), a mixture of lanthanum oxide and titanium oxide (La 2 0 3 .2TiO 3 a mixture of mixed barium and titanium oxide and yttrium oxide (BaTiO 3

.Y

2 0 3 and associations thereof.

The best results have been obtained from barium fluoride (BaFZ) and the BaTiO 3

.Y

2 0 3 mixture in proportions from 70% to 30% for one of them and from 30% to 70% for the other of them. These products produce a minimum cathode drop and therefore a voltage saving.

The pressure of the mixture of rare gases is preferably from 1 to 10 mbars (1 bar l05 Pa) The or each blocking or complement rare gas is chosen from the group comprising argon, krypton and helium.

In a preferred embodiment, each cathode includes a metal cylinder whose inside face is covered with the active layer and a tubular ceramic jacket covers the outside face of said cylinder.

The ceramic can be silica, alumina (aluminum oxide) S 20 or a mixture of those oxides with each other or with o other oxides.

A second aspect of the invention is directed to the o o .use of a lamp as defined above for decorative colored lighting or in an illuminated sign.

Secondary features and advantages of the invention will emerge from the following description, which is given by way of example and with reference to the S. accompanying drawing, in which the single figure shows in 0: longitudinal section one end of a discharge tube fitted with a hollow cathode electrode.

In the chosen embodiment shown, the luminescent/fluorescent mercury-free lamp 1 has a rectilinear or other shape hollow tubular glass body 2.

The glass is chosen from the glasses conventionally used for fluorescent tubes, namely hard glasses based on borosilicate, leaded or unleaded soft glasses, and alkali-lime soft glasses. In practice, the inside diameter of the hollow tubular body 2 is from 4 to 36 mm and the wall thickness from 1 to 1.3 mm.

The inside of the tube is covered with a conventional fluorescent powder or a mixture of conventional fluorescent powders, in practice to a thickness from 6 to 12 pm.

A central current feed conductor 3 or two lateral conductors, made of a nickel-based alloy and welded at one end to a metal cold hollow cathode electrode 4, pass(es) through the glass at each end of the body 2. The hollow tubular body 2 has a second electrode of this kind at the opposite end, of course.

The electrode 4 includes a metal support 5 in the form of a cylinder closed at the end welded to the central conductor 3 and coaxial with the axis of the tubular body 2. In longitudinal section, the cylindrical support 5 is U-shacec.

20 The metal support 5 is preferably made of Telar Low Carbon ultra-pure (99.99% pure) iron and is protected by nickel-plating with no brightening agent to a thickness of 4 to 8 Vtm or by controlled oxidation in order to obtain a blue oxide/black magnetite deposit.

25 The inside face of the metal support 5 is coated with an active layer 6 obtained by coating that face with a powder based on the compounds and/or mixtures defined hereinabove. BaF 2 or a BaTiO 3

.Y

2 0 3 mixture is preferably used in proportions from 70 to 30% for one of them and to 70% for the other of them.

An amou-nr from 4 to 12 mg of this kind of powder is typically applied to the inside face of the metal support A ceramic jacket 7 surrounds the outside of the metal supp:r: 5 to increase the service life of the

II

hollow cathode electrodes 4 and their resistance to demetallization caused by repeated impact of ions and electrons inside the hollow tubular body 2. The ceramic can be silica, alumina or a mixture of these oxides with each other or with other oxides.

A non-porous steatite shield 8 and a mica washer 9 supporting the cylinder 5 complete the electrode 4. The shield 8 is intended to prevent erosion of metal from the front edge of the cylindrical metal support Finally, the hollow tubular body 2 is filled with the mixture of rare gases with a purity from 40 to 55 N, including at least 90% neon and up to 1% of a blocking or complement gas or gas mixture chosen from the group comprising argon, krypton and helium, the remainder being xenon.

Depending on the diameter of the hollow tubular body 2, the filling pressure varies from 1 to 10 mbars in practice.

-With regard to the fabrication of this kind of lamp i, note that the inside of the tubular body 2 can be powder-coated dry or wet using ethyl acetate or demineralized water with additives, before it is baked in ooooo: an oven to obtain a perfectly homogeneous deposit of fluorescent powder(s) The cold hollow cathode electrodes 4 are then fitted and the tube is sealed at both ends.

The enclosure obtained in this way is then bombarded by electrical discharge inside the partially evacuated enclosure (residual pressure approximately 10 3 mbars). The enclosure is then degassed to a pressure less than 10 3 mbars, typically 10-6 mbars, before filling it with the mixture of neon, xenon and blocking or complement gas at a very low filling pressure from 1i to mbars.

It has been found that with a filling pressure of 3 mbars for a mixture of rare gases containing 1% xenon, optimum luminance is typically obtained with a very low operating current, of the order of 25 mA, using a fluorescent powder with the maximum emission at 525 nm.

The cathode drop and the tube voltage are then at a minimum, the voltage saving compared to a mercury tube being Of course, the invention is not limited to the example described above, but encompasses all variants thereof evident to the skilled person.

Claims (9)

1. A mercury-free lamp with activated cold hollow cathodes, including a glass tubular hollow body whose interior is covered with a fluorescent powder, which has at its two ends activated cold hollow cathode electrodes and which is filled with a mixture of rare gases, wherein the mixture of rare gases includes 90% to 99% neon and up to 1% of a blocking or complement rare gas or mixture of rare gases, the remainder being xenon, and the activated cold hollow cathodes have an active layer including barium fluoride (BaF 2 or a compound containing an element from group III B of the periodic table of the elements.

2. A mercury-free lamp according to claim 1, wherein the element from group III B of the periodic table of the elements is chosen from scandium, yttrium and lanthanum.

3. A mercury-free lamp according to claim 1 or claim 2, wherein the compound is chosen from the group comprising lanthanum oxide (La 2 0 3 lanthanum hexaboride 20 (LaB 6 scandium oxide (Sc20 3 a mixture of lanthanum oxide and titanium oxide (La20 3 .2TiO 3 a mixture of mixed barium and titanium oxide and yttrium oxide(BaTiO 3 .Y 2 0 3 and associations thereof.

4. A mercury-free lamp according to claim 1, wherein the active layer includes barium fluoride (BaF 2 or a mixture of mixed barium and titanium oxide and yttrium oxide (BaTiO 3 .Y 2 Os) in proportions from 70% to for one of them and from 30% to 70% for the other of e* :them.

5. A mercury-free lamp according to any preceding claim, wherein the pressure of the mixture of rare gases is from 1 to 10 mbars.

6. A mercury-free lamp according to any preceding claim, wherein the or each blocking or complement rare gas is chosen from the group comprising argon, krypton and helium.

7. A mercury-free lamp according to any preceding claim, wherein each cathode includes a metal cylinder whose inside face is covered with the active layer and a tubular ceramic jacket covers the outside face of said cylinder.

8. A mercury-free lamp substantially as hereinbefore defined with reference to Figure 1.

9. Use of a lamp as defined in any of claims 1 to 8 for decorative colored lighting or in an illuminated sign. DATED this 21st day of May 2004 AUPEM SEFLI WATERMARK PATENT TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA KJS/JMN