Combined illuminating and germicidal lamp and method of making the same

Nov. 7, 1944. j. l. libby 2,362,384

COMBINED ILLUMINATING AND GERMICIDAL LAMP

AND METHOD OF MAKING THE SAME

Filed March 30, 1942

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Patented Nov. 7,1944

2,362,384

UNITED STATES PATENT OFFICE

2,362,384

COMBINED ILLUMINATING AND GERMICIDAL LAMP AND METHOD OF MAKING THE SAME

Jules L. Libby, Elgin, III.

Application March 3(

Claim.

This invention relates to gas discharge lamp fixtures of the type used for illuminating and germicidal purposes, and refers particularly to the lamps per se or tubes which provide the source of luminous or radiant energy of such lamp fixtures. Gas discharge lamp fixtures are usually equipped with one or more of these lamps or tubes each of which comprises an elongated cylindrical sealed glass envelope of relatively small diameter compared to length and containing an inert gas under low pressure, together with a small quantity of mercury; and electrodes at opposite ends of the envelope connectible with a source of energizing current for ionizing the gaseous contents of the lamp and producing a discharge within the tube between its electrodes.

Ordinary illuminating lamps or tubes of this nature have a coating of a fluorescent phosphor on the entire inside surface of the glass envelope which compound is excited by the ultra-violet light typical of the mercury spectrum created upon discharge of the tube and caused to fluoresce thereby to provide a source of light for illuminating purposes.

It is common knowledge to those skilled in the art that such gas discharge illuminating lamps are superior to the incandescent filament lamp most commonly used at the present time. The quality of the light produced by gas dis. charge lamps and their economy of operation makes them ideally suited for use in industry.

Wherever food products are handled, processed or packaged, however, it is important to render the food products as sterile as possible. To this end germicidal lamps have come into widespread use in the food industry. Germicidal lamps are similar to the ordinary gas discharge illuminating lamp and are used in conjunction with the illuminating lamps in the manufacture of many food products.

Germicidal lamps are also particularly useful in public places, offices, factories, and the like, where they act to destroy air-borne bacteria and thus remove a common cause of infection.

The tube of a germicidal lamp fixture, like that of the gas discharge illuminating lamp fixture, essentially consists of a glass envelope having sealed therein under low pressure an inert gas and a quantity of mercury, and employs electrodes at the ends of the envelope to effect ionization of the gas contents of the lamp to produce radiant energy in the form of ultraviolet light for sterilization of the food products or for disinfecting purposes. However, the glass

1, 1942, Serial No. 436,752 (Cl. 176—122) envelopes of such germicidal lamps are of special glass capable of enabling ultra-violet light waves to pass therethrough and impinge the food products subjected to the lamps.

Thus while ultra-violet light waves are created by the discharge in both types of tubes, the nature of the glass envelope and the fluorescent phosphor compound thereon in the illuminating tube precludes the passage of ultra-violet light 10 therethrough.

Because of this fact, present equipment in the food industry consists in conventional fluorescent lighting fixtures and separate ultra-violet light fixtures, the first designed to provide a 15 source of illumination and the latter providing a source of ultra-violet light capable of killing bacteria, germs and the like.

The resulting duplication of lighting fixtures is obviously objectionable.

The present invention has as its main object to eliminate the necessity for duplication of light fixtures in the food industry through the provision of a single gas discharge lamp capable of emanating both luminous energy for illuminat25 ing purposes and radiant energy in the form of ultra-violet light for sterilizing purposes.

More specifically, this invention has as its object the provision of a gas discharge lamp or tube, the envelope of which is formed of special 30 glass to enable ultra-violet light waves to pass therethrough and which has predetermined portions thereof coated with a fluorescent phosphor compound to provide a source of illumination in addition to a source of ultra-violet light for ster35 ilizing and disinfecting purposes.

Another object of this invention resides in the provision of a simple method for making a combined illuminating and germicidal gas discharge lamp of the character described.

With the above and other objects in view, which will appear as the description proceeds, this invention resides in the novel method and in the novel combination and arrangement of mechanical expedients for carrying the same 45 into effect, substantially as hereinafter described, and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the 50 scope of the claim.

The accompanying drawing illustrates two complete examples of the physical embodiment of the invention constructed according to the best modes so far devised for the practical ap55 plication of the principles thereof, and in which:

8,369,384

Figure 1 is a side elevational view of the complete gas discharge lamp embodying the principles of this invention;

Figures 2, 3 and 4 are perspective views of the special glass envelop illustrating the first two steps in the method of making the same;

Figure 5 is a diagrammatic view illustrating the final step in the method of making the envelop of the tube; and

Figure 6 is a view similar to Figure Ί illustrating a modified form of lamp.

Referring now particularly-to Figure 1 of the accompanying drawing, the numeral 10 designates generally a gas discharge lamp or tube the envelope II of which is constructed in accordance with the principles of this invention. The envelope 11 is made from a piece of glass tubing of substantial length as compared to the diameter of the tube.

Plugs 12 cover the seals at the opposite ends of the envelop which confine therein under low pressure a quantity of inert gas of the type used in gas discharge, tubes for illuminating purposes and a small amount of mercury.

The plugs 12 carry prongs 13 on their exteriors adapted to be received in suitable sockets (not shown) and electrodes 14 interiorly of the envelope. As is customary, the impression of a suitable high voltage current across the electrodes 14 of the tube produces a discharge within the envelope to create a mercury spectrum which provides a source of radiant energy in the form of ultra-violet light.

Inasmuch as the gas discharge tube of this invention is designed to provide a source of both luminous energy for illuminating purposes and radiant energy in the form of ultra-violet light for sterilizing and disinfecting purposes, it is essential that the glass envelope 11 be formed of a special glass capable of passing ultra-violet light waves therethrough. These ultra-violet light rays are produced in all gas discharge lamps used for illuminating purposes which employ mercury vapor, but the major portion of the waves are prevented from passage through the walls of the glass envelope due to the customary coatings of fluorescent phosphor on the interior surfaces of the envelope and due to the nature of the glass itself.

In illuminating tubes, the entire interior of the envelope 11 is coated with a fluorescent phosphor material which is excited by the ultra-violet light waves created upon energization and discharge of the tube and caused to fluoresce, which fluorescence is utilized for illumination.

In the present invention, the interior surface of the special glass envelope is only partially coated with a fluorescent phosphor material so that relatively large coated portions 15 and uncoated portions 16 occur throughout the length of the tube.

The uncoated portions 16 act as windows through which the ultra-violet light rays created upon energization of the lamp pass to impinge and sterilize any food products subjected to the rays of the lamp.

As will be apparent, any desired proportions between the coated and uncoated surface may be employed to meet the requirements at hand, but for maximum illumination the coated areas IS of the tube are preferably arranged in the form of a spiral band as shown, extending continuously from one end of the tube to the other.

With the coated portions in this form it will be readily understood that with a given width of the βΙΟ

IS

2ft

3U fluorescent phosphor band any desired area of the tube may be coated merely by variation in the pitch of the spiral.

Consequently, any selected quantity of ultraviolet light may be obtained by regulation of the area of clear window space on the envelope, and such quantities of ultra-violet light which are detrimental to the human body or to certain processes may be readily avoided.

One method of making the envelope for the combined illuminating and germicidal lamp is as follows:

An envelope It of special glass capable of allowing ultra-violet light waves to pass therethrough has its entire interior wall surfaces coated with a fluorescent phosphor compound II as shown in Figure 3. Any suitable manner of introducing the powder into the envelope may be employed. The envelope having its interior sur20 faces thus coated with fluorescent phosphor material is heat treated to effect a degree of bonding of the phosphor material to the glass wall of the tube, which heat treating step may If desired be carried out in an oven 18, such as shown in Figure 4.

After the fluorescent phosphor compound has been baked onto the inner wall of the tube in this manner, portions of the coating are removed to form the clear window portions 16 on the tube through which the ultra-violet light created by the discharge of the tube passes.

Although any suitable manner may be employed for removing portions of the phosphor coating it has been found desirable from the standpoint of controlling the proportions of coated and uncoated portions on the envelope to rotate the envelope at a uniform rate while a scraping tool or wheel 19 is passed longitudinally through the tube from one end to the other in contact with the inner wall of the tube as shown at 20 in Figure 5.

This manner of removing portions of the phosphor compound enables very accurate control of the amount of ultra-violet light emanating from the tube, which of course, is desirable as an excessive quantity is injurious to humans and as indicated in Figure 5 the clear area should not exceed substantially one-half of the total area.

As will be apparent, longitudinal motion of the tool 19 through the tube in contact with the inner wall thereof results in the formation of adjacent spirals of coated and uncoated portions of the envelope along its entire length.

After the tube has been treated for the removal of portions of the phosphor compound, it may be completed in a manner well known to the art and which includes sealing a quantity of an inert gas and mercury inside the envelope under low pressure and applying the plugs 12 to the ends of the tube.

While a hot cathode type of gas discharge tube has been illustrated in Figure 1 of the drawing, it will be readily apparent that this invention is also adaptable to gas discharge tubes of the cold cath05 ode type.

For small wattage consumption, the lamp construction illustrated in Figure 6 has been found desirable. In this embodiment of the invention an outer envelope 21 which may have a shape similar to conventional incandescent bulbs or lamps encloses a small gas discharge tube II'. The tube II' is bent to approximately U-shape and has its ends provided with electrodes 14' electrically connected to a screw plug 22 at the sealed end of the outer bulbous enclosure. Both

2,363,384 the tube II' and the enclosure 21 are of special glass through which ultra-violet light may pass.

In this instance, however, interior portions of the outer bulbous enclosure are coated with the fluorescent phosphor compound as at 15, with only the lower half of the bulb 2 ί coated so that ultra-violet light created by the discharge tube II’ passes through the upper half of the bulb adjacent to its sealed end.

From the foregoing description taken in connection with the accompanying drawing, it will be readily apparent that this invention provides a combined illuminating and germicidal tube or lamp for gas discharge lamp fixtures whereby single fixtures employing one or more such tubes are capable of supplanting the dual lighting fixtures in use at the present time; and that the method for making the lamp of this invention is extremely desirable due to its simplicity.