US2625670A - Ultraviolet lamp - Google Patents

Description

Jan. 13, 1953 G. F. EMBSHOFF 2,625,670

ULTRAVIOLET LAMP Filed Oct. 1, 1948 5 Sheets-Sheet l ATTOR N EYS Jan. 13, 1953 G. F. EMBSHOFF ULTRAVIOLET LAMP 3 Sheets-Sheet 2 Filed Oct. 1, 1948 ATTORN EYS Jan. 13, 1953 e. F. EMBSHOFF ULTRAVIOLET LAMP 5 Sheets-Sheet 3 Filed Oct. l 1948 mm mm DUN can

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ELIN I XHVHLIEIHV Patented Jan. 13,

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"s'ignor 'to Institutum DiviThoma-e Foundation, tlincinnatigoliio, a corporation of Ohio ApplicationOctober 1, 19 48 SeriMfNw52363 4 Claims. 01. 3 15 49) This invention l'rielates .to ultraviolet'arc lamps and more particularly to ultraviolet lamps o'r burners of thetypefsold to the generallfpublic for use as sun lam'p's.

The usual method of providing ultraviolet radiation 'in sun ilamps .is .tofoper-atea mercury vapor arc in series with a suitable ballast -re sistance. Thedesi'rableiand beneficial'ultraviolet "wave lengths are thoselongerfthan about 28.00

Angstroms, whereas shorter wave lengths fmay haveharmful efiects. Sincethe spectrum ofthe mercury arc :con'tains substantial amounts of energy at these'undesirable shorter wave lengths, the usual-practice in sun lamps-isto enclose the arc in glass which filtersoutmost ii noti-all-of the radiation'below-about 2800;Angstroms. .On

the other hand, as the operating temperature and vapor pressurein the arc-increasatheultraviolet ener y output inthe region of the desirable longer wave lengths mentioned above-also 20 increases. Hence for sun lamp-purposes, it is advantageous to utilize the heat :developeiby the ballast resistance to increase the operating temperature of thearc -.and with it the-vapor pressure to a -value :approachin-g --atmospheric pressure 'as pointed; yout in -greater detail :hereinafter.

It hasialso beensa {common practice to combine the arc bulb :and ballast i resistancejinia unitary assemblage adapted? for simpleand :easy

connection to and disconnection from its gbase .or-housing as:-.a ;.unit. -,-Asrshown?in theprior U; S. Patent No; 2,369,987,:for example, the opposite endsof the-elongateda'rc 'bulbor tube, have been inserted in ceramic sleeves, the ballast resistance wire vbeingthreaded :back and forth shown in the prior patent,-;suchssleeves were-expensive and the time and filaborz-required to thread the resistanceewire; and'complet'e thesde- .vice was excessive. Still further, ;in :case fOf burning out of either the'tube or the ballast,

it was necessary to replace the -entire-,-assembly of tube, sleeves, and-ballast.

Inasmuch as sun lamps are (ordinarily used only forfbrief periods -of. -10-15'- .m-inutes, it is- -important to bring thewarcrtolthe desiredoperating temperature sand vapor pressure as quickly ;--as

possible so "that a substantial part of the period of exposure remainsinflwhichto-realizethe benefitsimeritioned'above. ."O'neof'the objects of the ,present invention is to provide an improved 'a'rrangeinent of ballast resistance relative .to the arc Ibulb which facilitates rapid heating of the bulb withoutinterfe'ring with the emission .of

ultraviolet radiation therefrom to .Ithe surround- .ing atmosphere. 7

.Another object of ,the invention is to provide theballast'resistancein the form ofa unit separate from the-arc tube the latter being separately removable from and replaceable in the lamp. t t

A; further object isto;eliminate-sleeves of the type described, above; and the time'and I labor required to thr-ead the ballast wire and toprovide ea cheaper and more -effective 'type =-of ballast adapted "to be -installed as a separate prefabricated unit in the -lam-p base or housing.

Still furthe'r objects are't'ogprovidenovel-means for mounting the tube and ballast unit and for housing and shielding the ends ;and electrical connections thereQf which :means are; simple and inexpensive, adapted :for man-uiacture by quantity production methods and apparatus, and -at the same time effective and reliable.

. nesem d ime tio t iin i ha b e l-u t a n atheficc m any d aw s, abu t s-t b ,zexr re tund rsto d th sa d a ings e 'i p r o e 10 i lus ratio nly a d lare'not to' besta-ken as ;a definition Lof the limits ofthe invention, reference bein bad to the appended c ims iorrthisznu 11 th drawin s, ;Fig. 1 is a diagrammatic ,iillustration of the p i ipal elements :and-athe circuit of a lamp suitable-{orthegapplication-oftheinvention;

5Fig. 2;is agpl'an:viewnpartlydn section, of a :rpreferred embodimentpfthe invention in a' lamp same general type as the lamp of the prior patent mentioned above. A lamp base is provided near its opposite ends with supply terminals 2, 3 which preferably are of the plug-in type for convenient connection to a source of supply indicated at 4. The ballast resistance is preferably divided into two parts and 6, although this division is not essential. The arc bulb 1 contains main arc electrodes B and 9 adjacent its opposite ends, and the ballast resistance is connected in series with the are path between these electrodes in any suitable manner. In the form shown, this is accomplished by connecting the ends of resistance 5 to the supply terminal 2 and the electrode 8, and the ends of resistance 6 to the supply terminal 3 and the electrode 9.

To facilitate starting the arc, filaments It and II are associated with the electrodes 8 and 9 respectively, one end of each filament beingconnected with its associated electrode to the end of the ballast resistance 5 or S. The other ends of the filaments Ill and II are connected to terminals l2 and I3 respectively, and a starting switch I4 is connected between these terminals. The starting switch may be operated manually if desired, or may be of any suitable type adapted to open automatically after a brief time period. When the starting switch is separate from the lamp unit, as in the form shown, the terminals I2, I3 are preferably of the plug-in type like the terminals 2, 3.

The are bulb contains a quanity of vaporizable and i'onizable material such as mercury, and is usually filled with argon or other suitable rare gas at a low pressure. The starting filaments I0, II are coated with or otherwise embody a suitable electron-emissive substance. When the lamp is connected to the supply 4, current fiows through a series circuit comprising terminal 2, resistance 5, starting filament I0, terminal 12, starting switch I4, terminal I3, starting filament I l, resistance 6, and terminal 3. As the filaments become hot, electronic emission therefrom will result in ionization of the atmosphere in the arc bulb. After a brief initial period, the starting switch I4 is opened to break the series circuit described above and the main arc strikes between the electrodes 8 and 9 through the ionized atmosphere, the current then flowing in series through the arc path and the resistances 5 and 6.

Figs. 2 6, inclusive, show a practical embodiment of the invention in a lamp of the type described above with reference to Figure l. The base I comprises a sheet metal plate shaped by a stamping or pressing operation to the form hereinafte described. A-t opposite ends, this base plate carries mounting blocks I5 and Id of suitable insulating material, the terminals 2, 3, I2 and I3 being mounted in these blocks with their plug ends projecting below the base through openings I! cut out of the sheet metal base plate for this purpose. The mounting blocks are secured in place by turned-up flanges of the base plate along the sides of the blocks as shown at l8 and across the ends of the blocks as shown at I9. The end flanges I9 are provided with tabs turned over and pressed down on top of the mounting blocks, and preferably the end of each block is recessed centrally at 2| and a portion 22 of each end flange is bent inwardly into the recesses 2| to hold the blocks firmly.

At the inner ends of the mounting blocks, plate-like supports 23 and 24 project upwardly from the base in planes substantially at right angles to its length, being spaced apart by a dis- 4 tance at least co-extensive with the length of the arc path between the electrodes 3 and 9. These supports are also formed from sheet metal and are each provided with a central flange 25 turned horizontally and engaging the upper surface of the inner end of the mounting block (Figs. 3 and 6) and with tabs 26 projecting downwardly on either side of the flange 25 into engagement with the base plate I. Additional tabs 21 extend at right angles from the vertical outer edges of the tabs 26, these tabs 21 being insid the flanges H of the base plate and having lugs 28 which extend down through openings in the base plate and are suitably deformed to hold the supporting plates firmly in position as shown in Figure 6.

The spaced supporting plates 23 and 24 enable the arc bulb 7 and the ballast resistances 5 and 5 to be mounted in parallel closely adjacent positions therebetween so that the entire length of the arc is exposed to emit ultraviolet radiation while at the same time the heat from the ballast resistances is distributed throughout the length of the bulb. To thi end the resistances 5 and 3 are made rigid and self-supporting between the plates 23, 2d, and in the form shown comprise coils of resistance wire inserted in supporting tubes 29 and 39 of heat resistant ceramic or other suitable material. These tubes heat up very rapidly to a relatively high temperature so that heat is quickly available to raise the operating temperature of the arc. The are bulb and the tubes are quickly and easily mounted by inserting their ends in suitable openings formed in the supporting plates. Preferably the tubes 29, 30 are located between the arc bulb I and the base plate I, one tube on each side of a longitudinal plane through the center lines of the arc bulb and base. The base plate may be dished upwardly between the supporting plates as indicated at 3! in order to strengthen the base plate and to provide a reflecting surface close to the tubes 29, 30 and are bulb 1, thereby increasing the effective output of the lamp and minimizing dissipation of ballast heat to the surrounding atmosphere.

Thus the arc bulb and the resistor elements are independently mounted and are separately removable and replaceable in case of need. Installation and connection of these elements, as well as removal and replacement thereof, are facilitated by the fact that their ends are exposed beyond the supporting plates 23, 24 so that the necessary electrical connections are accessible and can easily be made or broken. In the form shown, these electrical connections correspond to the diagram of Fig. 1 in the following manner. One end of the resistance 5 is connected by a wire 32 to the supply terminal 2 to which it is anchored by a nut 33. Similarly the opposite end of the resistance 6 is connected by a wire 34 to the terminal 3 to which it is anchored by a nut 35. Suitable leads from the electrodes 8, 9 and filaments I0, I I project outwardly through the press 38 at each end of the arc bulb. Atthe right-hand end of the lamp, one lead 31 of the filament I 0 and both leads 38 of the electrode 8 are combined at 39 and connected at 36 to a wire ll that leads to the end of the resistance 5. The remaining lead 42 of the filament I0 is connected to the terminal I2, and may as shown be passed through a small hole in the connecting block l6 and anchored to the terminal underneath the block, although this is not necessary. Similar connections are made at the left-hand end of the lamp, one lead 43 of the filament II and the two leads 44 of the electrode 9 being combined at and connected at. 45 to a wire 41 leadin to the end of the resistance 6. The re maining lead 48 of the filament H passes through a hole in'the mounting block. I5 and .is connected I underneath the block to the terminal [3.

The electrical connections at both ends of, the lamp re thus readily a cessible in case of need. but normally are enclosed and. protected by removable metal hoods which cooperate with the ends of the base plate and with the supporting plates 23, 24 to form. closed compartments around the ends of the arc bulb and ballast resistors at both ends of the lamp. These hoods are preferably made of sheet metal parts p perly out and shaped by stamping or pressing and assembled permanently in any suitable manner as by spot welding. In the form shown, each hood comprises a flat end plate 49. and a u-shaped hood member havin a. flange 5| turned' ver and secured to the edge of the end plate 49 and a similar flange 52 adapted to engage over the edge of the supporting plate 2.3 or 24. These hoods are attached to the lamp in any suitable manner such that they can be removed quickly and easily whenever desired. In the form shown, the end plate 49 is formed with a lug 53 adapted to snap over the end flange I9 of the base plate and to engage in a notch therein, and each side of the hood member 50 has a similar lug 54 adapted to snap over and engage in 3 notches in the side flanges ll}. of the base plate. The hoods may be lined with heat resistant material such as asbestos as shown at 55 (Fig. 3), which aids in keeping the ends of the lamp hot and preventing condensation of mercury therein.

The embodiment Of the invention illustrated in Figs. 7-9 is adapted to be. plugged in at one end and has all four plug, terminals projecting from one end instead of in pairs projecting from the side of the base as in the previous embodiment. Thisarrangernent may be convenient for use with certain types of lamp mounts. In this case it is convenient also to connect both ballast resistances in series between one end of they are and the supply line, instead of arranging them as describe b ve.

Referring to Figs. 7-9, the base plate 6.0 and supDQrting plates 61,62 correspond with and are similar to the base plate, I and supporting plates 23, 24' of Figs. l-6. The plates El, 62 serve to support an arc bulb 63 containing arc electrodes 64 and starting filaments 65 near its opposite ends, as well as a pair of ballast resistor units 66, 61, which elements may also be similar to the corresponding elements of Figs. 1-6.

Instead of two mounting blocks, a single mounting block 68 is located at the lower end of the lamp in a plane at a right angle to the base plate and carrying four terminals projecting from the lower end of the lamp. One pair of terminals 69, 10 on one side of the lamp (Fig. 8) serves as supply terminals. The other pair of terminals on the other side of the lamp, one of which is shown at I I, serves to connect the starting filaments to the starter switch as described above. Thus the triple lead, [2 from electrode 54 and one end of filament at the lower end of the lamp are connected to supply terminal 69. The. corresponding triple lead 13 at the top is connected to the lower end oi the resistor 56, passing for this purpose through an insulator tube l4 paralleling the resistor and mounted with it in the supporting plates 61, 62, The upper end of resistor 66 is connected" at I5 with the upper end of the resistor 61, and the lower end of the latter i connected by a lead 16 to the other supply terminal it. To complete the starting circuit, the lead ll from the lower starting filament is connected to the front terminal H, and the correspondinglead [8 from the upper filament passes through an insulator tube 19 similar to the tube 14 and is connected to the other terminal 1| (not shown).

The mounting block 6-8 is supported by a sheet metal frame or casing connected to the base plate in any suitable way and preferably forming the end plate of a hood 8| enclosing the lower end of the lamp. The upper end is provided with a similar hood 82 the end plate 83 of which is domed and preferably provided with a ventilator 84.

In operation, the main arc starts when th arc bulb is relatively cool and the mercury vapor pressure is correspondingly low so that the arc first operates at relatively low voltage and high current. However, due 'to the heat generated in the arc itself and to the heat supplied by the ballast resistors, the operating temperature and mercury vapor pressure increase rapidly, accompanied by a, corresponding increase in the voltage across the are which is closely related to and varies with the pressure. Assuming a suflicient quantity of mercury in the bulb, the arc will stabilize at a final operating pressure and corresponding voltage the values of which will depend primarily on the amount of heat generated and the amount dissipated to the surrounding atmosphere.

The present invention relates particularly to sun lamp burners adapted to operate at the normally available househld voltage of volts, the length of the arc path between the electrodes being within the approximate limits of 1-3 inches. Under these conditions arc voltages, expressed either as total arc voltages or as volts per inch of length of the arc, correspond closely with definite mercury vapor pressures. Thus in lamps of this type either are volts per inch, or the correspond.- ing mercury vapor pressure, may be used as an index of the energy distribution of the are which varies with operating temperature and pressure as stated above.

Fig. 10 shows the variation in the amount of energy emitted by lamps embodying the inven tion at representative wave lengths in the desirable ultraviolet region in relation to are volts per inch. Itv will be observed that at arc voltages less than about 20 volts per-inch. the amount of energy emitted in the desirable region is very small as compared with optimumv operating conditions. The mercury vapor pressure correspond ing to 20 volts per inch is of the order of 6.00 mm. of mercury. It is necessary to brin up the temperature and vapor pressure of the arc bulb to this point in, order for the lamp to operate with satisfactory eificiency as a. sun lamp. Moreover, it is important to reach. these operating conditions as rapidly as possible since otherwise the desired benefits of the radiation to the user will be greatly decreased.

On the other hand, if the pressure in the bulb becomes too high, the-arcwill go out. This results when the voltage necessary to cause the arc to strike between the electrodes becomes greater than that available under the conditions prescribed above. In lamps embodying the invention and conforming to the limiting conditions stated above, the safe upper limit of arc voltage for practical purposes is about 40 volts per inch which corresponds to a mercury vapor pressure of the order of 760 mm. of mercury.

An important advantage of the abovedescribed arrangement of the bulb and ballast is that it satisfies the operatin requirements prescribed above. The amount of ballast resistance can be made small enough to provide the required voltage drop across the arc and to eliminate prac tically the danger of overheating to the point where the arc goes out, while at the same time the high temperature ceramic tubes and their arrangement relative to the bulb cause the tube to heat rapidly to the necessary minimum pressure. As an actual example, excellent results were obtained with an arc bulb about 1%, inches in diameter and 5 inches long, the arc length between the electrodes being approximately 2 inches, and a ballast resistance of 21 ohms divided into two sections of 10.5 ohms each. The ballast resistors may suitably comp-rise coiled Nichronie wire inserted in thin-walled ceramic tubes. The Nichrome wire being made as small as possible and still carry the current, the temperature of the ceramic tubes was of the order of 1100" F. On a line voltage of 120 volts, this lamp operated with an arc voltage of 40-55 volts (-225 volts per inch), current of 3.0-3.5 amperes, and wattage of 150-165 watts.

Fig. 10 shows the importance for sun lamp purposes of maintaining the arc voltage within the prescribed range. The importance of reaching this range as rapidly as possible will be appreciated from the following comparison of a lamp as described above with a lamp of the type shown in Patent No. 2,369,987 mentioned above. The latter required about 14 minutes to reach an arc voltage of about volts and about 29 minutes b0 stabilize at about 37 volts. Bearing in mind that the average period of exposure to such lamps is only about 10-15 minutes, it is apparent that users of the prior lamp do not realize the benefit of its most favorable operating conditions unless it is turned on and allowed to stabilize in advance of use for a period roughly equivalent to the period of exposure itself. Moreover even after stabilization the arc voltage (37 volts=18.5 volts per inch) was so low that the amount of energy emitted at the desirable wave lengths was sharply curtailed and unsatisfactory, as will be appreciated from Fig. la). In contrast, the arc voltage in the lamp embodying the present invention increased very rapidly and reached 40 volts (20 volts per inch) within about six minutes, with approximately half the normal period of exposure still remaining.

The arrangement of the ballast resistance in the form of elongated elements paralleling and closely adjacent to the arc bulb throughout its length contributes materially to the realization of the above advantages, since ballast heat is thereby made available quickly and is distributed substantially uniformly throughout the length of the arc path. This desirable arrangement is facilitated by the use of the tubes 29, 30 which provide rigid self-sustaining resistor units in a simple relatively inexpensive form. The are bulb and the resistor units can be mounted very quickly and at the same time accurately and firmly by inserting them in the openings in the supporting plates 23, 24. With the hoods removed, more over, the electrical connections are all accessible so that the tube and resistors can be installed and connected conveniently, or any of them can be separately removed and replaced with equal ease.

The base plate, the supporting plates and the hoods can be made cheaply in large quantities by simple sheet metal pressing or stamping operations, and can be assembled quickly and easily. The entire length of the arc is exposed between the plates 23, 24 for efiective radiation, without interference from the ballast resistors which nevertheless supply heat to the arc bulb throughout its length. The hoods enclose and protect the electrical connections and thus complete a lamp unit that is relatively inexpensive but safe and convenient to use, neat and attractive in appearance, and efiicient in operation.

While only one embodiment of this invention has been described and illustrated in the drawings, it will be understood that the invention is not restricted to this embodiment but is capable of various modifications and changes in the details, form and arrangement of the various parts. Reference should therefore be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

l. A lamp of the type having a tubular arc bulb and an elongated ballast resistor comprising an elongated substantially flat base, a supporting plate near each end of said base extending transversely across and projecting outwardly from said base in a plane substantially at right angles thereto, aligned openings in said supporting plates through which the opposite ends of said bulb and ballast resistor project whereby they are supported in spaced substantially parallel relation with one another and with said base, lamp terminals at at least one end of said base and connections between said terminals, bulb, and resistor, and housing members one secured to and cooperating with each end of the base and the adjacent supporting plate to form therewith a compartment enclosing the ends of said bulb and resistor and certain of said connections.

2. A lamp as defined in claim 1, said housing members comprising heat insulating material for retaining heat in said compartments around the ends of said bulb.

3. A lamp as defined in claim 1 having two ballast resistors mounted in laterally spaced substantially parallel positions at substantially equal distances from said base, said bulb being mounted outwardly of said resistors with its axis in a plane passing between said resistors and through the center line of the base.

4. A lamp as defined in claim 3, a portion of said base between said supporting plates being dished outwardly adjacent said ballast resistors and forming a reflecting surface.

GEORGE F. EMBSHOFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,182,732 Meyer Dec. 5, 1939 2,259,915 Weritz Oct. 21, 1941 2,291,926 Sperti Aug. 4, 1942 2,301,670 Abadie Nov. 10, 1942 2,327,346 Furedy Aug. 24, 1943 2,327,755 Abernathy Aug. 24, 1943 2,342,570 Biller Feb. 22, 1944 2,369,987 Sperti Feb. 20, 1945 2,448,937 Walter Sept. 7, 1948

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