US2025182A - Ultraviolet lamp - Google Patents

Description

Dec. 24, 1935. G. sPERTI ULTRAVIOLET LAMP Filed Feb. l5, 1932 2 Sheets-Sheet ll MA-si Dec. 24, 1935. G. sPERTl ULTRAVIOLET LAMP Filed Feb. 13, 1932 2 Sheets-Sheet 2 Patented Dec. 24, 1935 UNITED STATES v2,025,1a2 i LTRAWOLET LAMP' George Sperti, Covington, Ky., assignor to Sperti Lamp Corporation, New York, N. Y., a corpora.-

tion of Delaware Application February13, 1932, Serial No. 592,742

4 Claims.

This invention relates to light sources which emit principally inthe ultra-violet portion of the spectrum and more particularly to ultra-violet arc lamps.

In recent years the use of ultra-violet light for various purposes has greatly increased. For example, ultra-violet light is used to irradiate ergosterol and other foods for the purpose of creating antirachitic properties therein; for the direct irradiation of both human beings and animals as a protection against rickets and for general health purposes; the use of ultra-violet light has been suggested for hatcheries and stables, for the sterilization of foods and other products, etc. In some cases, the use of ultra-violet light requires radiations of predetermined wave lengths such as Wave lengths longer than 2900 angstrom units, because shorter wave lengths may produce harmful results in such cases as the activation of foods, irradiation of human beings, plants and animals, etc. In other cases, such as sterilization, the short wave length limit may be different or it may be desired to use all of the ultra-violet light available.

In view of these increased uses of ultra-violet radiation, there has been an increased demand for suitable sources of ultra-violet light which operate efficiently and economically and do not require too much equipment in addition to the lamp itself. 'Ihe most suitable source of ultraviolet has thus far been found to be an arc between suitable electrodes in an atmosphere of ionized gas or vapor which may comprise mercury vapor, vapors of other relatively volatile metals, gases such as neon and argon, etc., the nature of the arc atmosphere depending to some extent on the radiations which are to be produced.

' The present invention relates to an arc lamp of this type radiating in the ultra-violet region of the spectrum and designed for any of the uses mentioned above wherein the ultra-violet radiation is of value. For such purposes the amount of ultra-violet radiation should be increased asmuch as possible and the visible radiation is not important.

One of the objects of the present invention is to provide an improved and novel ultra-violet lamp which is structurally simple and inexpensive to manufacture, economical to use, and eflicient in the production of the desired ultra-violet radiations.

Another object is to provide a novel arc lamp arranged to prevent the escape of heat from the lamp by conduction and convection so as to permit continued operation at temperatures which are most eilicient for the production of the desired 'ultra-violet radiation.

Another object is to provide a novel ultra-violet lamp wherein the arc temperature is increased and whereby higher boiling point elements can 5 be employed for the arc.

A further object is to provide a novel ultraviolet lamp wherein separate circuits are employed for heating the arc electrodes and for` supplying the arc current whereby the characterl0 istics of these circuits can be determined independently.

Another object is to provide a novel ultra-violet arc lamp which is self-contained and self-starting. I

With the above objects in view, the invention in its broader aspects includes suitable means for establishing and maintaining an arc in mercury or other vapor in a suitable bulb or chamber which is insulated to prevent the escape of heat, the bulb transmitting the desired radiations and withstanding the temperature developed. Ina preferred form, the arc bulb or chamber is suitably mounted and enclosed in an outer'bulb or chamber which is highly evacuated,` and the arc i chamber is mounted so as to reduce as much as possible the possible'paths whereby thermal conduction from the lamp can take place. In many cases the heat generated by the arc itself will be sufcient vto maintain the arc chamberl at the desired temperature, inv View of the provision of heat insulation, but if desired, additional heat producing means such as heating coils may also be embodied in the lamp, the effectiveness of such additional heating means being greatly increased by insulating the lamp. The heat insulation, with or without the heating coil, makes it practicable to operate the arc at a higher temperature and hence to increase the amount of ultra-violet energy emitted. The invention also makes it practicable to obtain arc spectra of other elements of higher boiling points such as magnesium, l cadmium, caesium, etc.

Two embodiments of the invention have been illustrated in the accompanying drawings, but it is to be expressly understood that said drawings are for purposes of illustration only and are not to be construed as a deiinitioA of the limits of the invention, reference being "had to the api pended claims for this purpose. v

In the drawings,

Fig. 1 is a view partly in section of a lamp embodying the invention;

Fig. 2 is a detail view, partly in section, of a portion of the lamp shown in Fig. l;v

Sig. 3 is a perspective view of another form of lamp embodying the invention; and

Fig. 4 is a sectional view of the lamp shown in Fig. 3.

Referring now to Figs. l and 2, the lamp bulb I is of any suitable type, size and shape and is mounted in any suitable base 2. The material of which the bulb I is made transmits ultra-violet light at least of the desired wave lengths. For

instance, the bulb may be constructed of quartz glass or oi' any other known glass which transmits ultra-violet radiations. Where it is desired to filter out the radiations shorter than a predetermined wave length, the bulb I may be of material having the desired filtering characteristics, al-

though these characteristics are not essential for reasons pointed out hereinafter. The base 2, in the form shown, is of a type analogous to that employed with radio tubes. Sealed in the neck of the bulb I is the usual stem or standard 2, of glass or other suitable material, which constitutes the usual means for introducing the necessary conductors into the lamp and for supporting the various elements within the lamp. The bulb I is evacuated, preferably to the highest practically dpossible degree. Mounted in any suitable manner within the bulb I is an inner bulb or arc v chamber 4 which as shown is supported by a band l and supports 2 and 1 that are fused in the standard 2. A stem or standard 2 is sealed in the neckof said inner bulb, and this bulb is also of material which transmits ultra-violet light and withstands the temperatures developed. Where it is desired to filter out radiations shorter than freely down to about 2000 Angstrom umts or below, while certain special glasses have very low transmission for wave lengths shorter than 2800` -to 2900Angstrom units. The structure thus far described and including the two bulbs and means for sealing and mounting the same is disclosed and claimed in copending applications and illlustrates a practical form of lamp in which the invention may be embodied.

While the are electrodes may have any suitable form, they are preferably of a typevwhich renders v the arc self-starting so as to avoid the necessity for tilting or otherwise manipulating the lamp inghigl'i electronic emission when heated such as thorium oxide, strontium oxide, barium oxide, etc. The sleeves 2 and |2 may be provided at their adjacent ends with caps ||y and I2 respectively which caps are formed of material which constitutes a good arcing surface, these caps being uncoated. Tungsten, zirconium oxide,

and the like are suitable materials for the arcing surfaces. The inner bulb also contains a quantity l of suitable ionizable material, the nature of which depends on the radiations to be produced.

A suitable lamp circuit is provided which not only supplies potential to the electrodes 2 and l2 but also includes means for heating the electrodes to start the arc, this heating causing electronic emission from the oxide coatings and ionizing the arc atmosphere. Preferably two sources of cur- 5 rent at different potentials are provided for heating the electrodes and for establishing the arc therebetween, and separate lamp circuits and terminals are provided in order that the characteristics of these circuits can be regulated and con- 10 trolled independently. Preferably also the leads within the arc chamber are prbtected in order to prevent the arc striking between the high Potential leads to the lectrodes, with constant dan'ger of 4burning them out, and to these ends the elec l5 trodes areshown supported in a manner described and claimed in a copending application of George Sperti, Serial No. 592,745.1ssued May l, 1934, as Patent No. 1,956,599. Within the arc chamber are tubes I2 and I4 of suitable insulating material 20 such as magnesium oxide, these tubes being arranged in spaced parallel relation and being secured together and carrying the electrodes between them by means of metal straps I5 and I 2 that are passed around the elements and crimped between the elements. The unitaryy structure thus formed, including the electrodes 2 and vIII and the tubes I2 and I4, is supported within the arc chamber by means of suporting wires I1 and I2 that are preferably welded to the lower me- 30 tallic strap I2 and` are fused in the stem 2.

For heating the electrodes 2 and I2, current is supplied by conductors I2 and 20 connected respectively to base terminals 2| and 22. The conductor I2 is connected to the supporting wire 1 35 and a wire 22 leads from the support 1 through the stem 8 and the insulating tube I4 to one end of a heating filament 24 within the electrode 2.

A wire 22 connected to the other end of the heating filament 24 passes through the insulating 40 tube I 2 and leads to one end of a heating filament 22 within the electrode I2. the other end of the filament 22 being connected to the wire 2li. Filaments 24 and 22 are insulated from the'electrodes in any suitable manner, as by coating them with a suitable refractory cement.

Arc potential is supplied to the electrodes 2 and I2 by wires 21 and 22 connected respectively w base terminals 22 and 22. 'I'he wire 22 passes through the stem 2'and the stem 2 and is con- 50 nected to the electrode I2 by means of the metal supporting strap I2. The wire 21 may be connected to the electrode 2 in a similar manner but for convenience is shown connected to the wire 2l, said wire being connected to the metal sup- 55 porting strap I5 by means of a wire 2|. i

Any suitable means may be employed for supplying current to the lamp, either in the form of two separate sources of different potential or as shown by two windings of a transformer. A suitable socket is shown diagrammatically at 22 which socket comprises four terminals. Socket terminals 22 and 24 engage the base terminals 2| and 22 respectively and are connected by wires 25 to a secondary transformerwinding 22 asso- 65 ciated with a primary transformer winding 21. Socket terminals 22 and 22 engage respectively base terminals 22 and 22 and are connected by wires 42 with a secondary transformer winding 4| associated with the primary winding 21.

When current is supplied to the transformer, the winding 22 is energized and current is supplied to a circuit including one of the wires 2i. terminals 22 and 2|, wire I2, support 1, wire 22, lament 24', wire 22 filament 22, wire 22, termi- 75 the oxide coatings of the electrodes.

Q l 2,025,182 l nals 2 and 34, and the other wire 35.' The heating iilaments 24 and 26 heat the electrodes 9 and I and also impart heat to the gas or vapor with- "in`the arc chamber which is quickly ionized by the heat and -also by the electronic emission from At -the same time the winding 4| is energized and arc potential ,is supplied to .the electrodes by a circuit comprising one of the wires 40, terminals and 30, wire 28, electrode I0, electrode 9, wire 3|, wire 25, wire 42l, - terminals 29 and 38, and the other wire 40.

As soon as the arc atmosphere becomes ionized the arc strikes between the electrodes 9 and l0. It will be seen that the only thermal paths from the arc chamber to the outside of the lamp are by way of the supporting wires 6 and 1. The evacuated bulb I constitutes an effective heat insulating means which surrounds the entire arc chainber but at the same time does not interfere in any way with ultra-violet radiation therefrom. 'I'he arc chamber therefore rapidly heats up to a relatively high temperature, due both to the heat from the filaments 24 and 26 and to the heat generated by the arc itself.

In most cases the heat generated in these ways will be sufficient to maintain the arc chamber at the desired operating temperature, but in some y instances, 'particularly where the arc chamber contains relatively high boiling point elements, additional sources of heat may be desirable. Figs. 3 and 4 illustrate a lamp embodying an additional source of heat for the arc chamber comprising a heating coil. For convenience, the lamp illustrated is generally the same as that illustrated in Figs. l and 2 except for the addition of a heating coil and hence corresponding elements posite ends of lthe coil 44 are connected to wires 45 and 46 which are in turn connected across the wires 2l' and 28 which supply potential to the electrodes 9' and I0'. The heat from the coil 44 assists in vaporizing and ionizing the arc atmosphere initially and in maintaining a high operating temperature in the arc chamber during arc operation.

The invention thus provides an arc enclosed within a. bulb or chamber and surrounded by an evacuated space which effectively prevents the escape of heat from the device. The eiect produced is analogous to that obtained in a thermos bottle, and the result is that the arc operates at a higher temperature than would be maintained `without the heat insulation. The ultra-violet radiation from an arc such as the mercury are increases in quantity as the operating temperature is increased. Moreover, when it is desired to use higher boiling point elements for the arc, the required operating temperature'. may be obtained in the arc chamber, the heating coil being added if necessary. Thus in addition to the usual materials such as mercury vapor and gases such as neon, argon, etc., it is possible to use materials such as magnesium, caesium, cadmium, etc., or

Preferably andin order to re- 3 their compounds, and to obtain the characteristic spectra of these materials. Magnesium, for exf not emit strongly at shorter waves lengths and hence-is very desirable for many purposes. The lamp is small and compact, substantially self-contained, and self-starting, and the separate circuits employed for heating the electrodes and 10 supplying the arc make it possible to determine the characteristics of these circuits independently. While only two embodimentsv of the invention havevbeen described and illustrated in the drawings, it is to be understood that the invention is 15 capable. of various physical embodiments and that changes may be made in the form, details of `construction and arrangement of the parts Without departing from the spirit of the invention. It will also be understood that the invention is not restricted to the particular type of lamp shown, to the particular form of electrodes or to the particular means for supporting the various elements within the lamp, which are here shownV merely to illustrate a practical form of lamp in 25.

which the invention may be embodied. Reference is therefore to be had' to the appended tclaims for a definition of the limits of the invenion.

What is claimed is: 1. An arc lamp comprising an outer bulb,'an inner bulb mounted therein and spaced from the Walls thereof, arc electrodes in said .inner bulb, an annular well formed in the wall of said inner bulb and containing a quantity of ionizable material, a heating coil in the space surrounded by said annular well, terminals Afor said lamps, and means for connecting said electrodes and coil to said terminals, said outer bulb being evactuated whereby said arc bulb and coil are completely 40 enclosed in an evacuated, heat insulating chamber.

2. An arc lamp comprising an arc bulb, a pair ofelectrodes and a quantity of ionizable material in said bulb, heating filaments for said electrodes, two pairs of terminals for saidl lamp, meansxcon- -V necting said filaments across one pair of termi-K hals, means connecting said electrodes to the other pair of terminals, and an outer evacuated bulb in which said inner bulb is enclosed.

'3. An arc lamp comprising an arc bulb, a pmr of hollow electrodes and a quantity of ionizable material in said bulb, heating laments within and insulated from said hollow electrodes, two pairs of terminals for said lamp, means connect- 55 ing said iilaments in series across one pair of terminals, means vconnecting said electrodes to the other pair of term'inals, an outer evacuated bulb, and means for supporting said arc bulb within and spaced from the walls of said outer bulb.

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