Electric Lamp With Protective Enclosure Having Shrunk Plastic Retaining Means

Abstract

The fragile glass envelope of a fluorescent lamp or similar device is enclosed in a tight-fitting sleeve of shrunk light-transmitting plastic to provide a shatter-proof and explosion-proof lamp. Various fluorescent lamp embodiments wherein the shrunk plastic sleeve is also utilized as a filter, a light-polarizing component, a radiation-converting medium, and as a means for encasing an exterior starting aid or reflector are also disclosed. In another embodiment the enclosure comprises a loose-fitting plastic jacket having shrunk ends, or a separate light-transmitting plastic jacket that is held in place on the lamp by a pair of overlapping shrunk plastic sleeves, so that the jacket serves both as a protective member and as a thermal insulating enclosure that permits the lamp to be used in outdoor lighting applications.

Description

This invention relates to electric lamps and has particular reference to a fluorescent lamp that is provided with a jacket or sheath which comprises an integral part of the lamp, and to a method for attaching a member to an electric lamp or similar device by means of such a sheath.

As is well known, the performance of fluorescent lamps is affected by ambient temperature. The light output falls off sharply when the temperature drops below 10.degree. C. or the lamp is exposed to cold winds or the like. For this reason, when fluorescent lamps are used for such outdoor lighting applications as street lighting, sign lighting, etc., they are enclosed in suitable fixtures. A more recent approach to this problem is to enclose each lamp in its own tubular shield or jacket that is held in spaced protective relation with the lamp by suitable gaskets fitted over the lamp ends. A so-called "jacketed" fluorescent lamp of this type is disclosed in U.S. Pat. No. 3,124,307 entitled "Vapor Lamp Units" issued Mar. 10, 1964 to T. E. Hoskins at al.

Another problem area derives from the fact that the envelopes of fluorescent lamps are fabricated from relatively thin-walled glass tubing and are, therefore, quite fragile. The lamps are thus mechanically weak and are easily and frequently broken during handling, shipping, etc.

It would be desirable to be able to modify the color or optical character of the light produced by a fluorescent lamp without altering the composition of the phosphor coating or redesigning the lamp--both of which are time-consuming and costly projects.

It is accordingly the general object of the present invention to provide a convenient and inexpensive means for improving the ruggedness, performance and versatility of electric lamps and similar devices having envelopes of vitreous or other frangible material.

A more specific object is the provision of an improved fluorescent lamp which is protectively enclosed by a structure that forms an integral part of the lamp and can be conveniently and inexpensively placed on the lamp after it has been fabricated.

Another object is the provision of an electric lamp having an inexpensive enclosure that modifies the color or optical characteristics of the light produced by the lamp and protects the lamp envelope.

A further object is the provision of a cheap light-modifying and protective component that can be slipped over and attached to the envelope of a fabricated fluorescent lamp or similar device quickly and on a mass production basis.

Another object is the provision of a method for attaching a component to a previously fabricated fluorescent lamp or similar electrical device without impairing its light output.

The foregoing objects, and other advantages which will become apparent as the description proceeds, are achieved in accordance with the present invention by enclosing all or part of the lamp in a sleeve that is fabricated from shrinkable light-transmitting plastic. Preferably, the sleeve is made of heat-shrinkable plastic that is initially of such dimensions and so oriented that it will fit loosely over the lamp and, upon being heated, will shrink and form a smooth tight-fitting sheath that conforms to the shape of the part of the lamp which it encloses.

In addition to protecting the lamp from breakage, such oriented plastic sleeves are used in accordance with the invention to modify the character of the light emitted by the lamp. Several fluorescent lamp embodiments are disclosed wherein this is achieved by utilizing sleeves made of a plastic which will polarize light, filter undesirable radiation such as ultraviolet radiation, or which contains fluorescent material that responds to radiation generated within the lamp and emits longer wavelength radiation that changes the color of the light emitted by the lamp.

Lamp embodiments wherein such shrink-fit plastic sheaths are employed to hold a conductive starting component, lead wires for a single-ended discharge lamp, and a tubular protective jacket in place on a finished fluorescent lamp are also disclosed.

A method for fastening a component to a previously fabricated fluorescent lamp or other device utilizing a heat-shrinkable plastic sleeve is also disclosed.

A better understanding of the invention will be obtained by referring to the accompanying drawing, wherein:

FIG. 1 is an elevational view of a fluorescent lamp provided with the shrink-fit plastic sheath of the present invention;

FIG. 2 is an enlarged cross-sectional view of the lamp along the line II--II of FIG. 1;

FIG. 3 is an elevational view of a single-ended discharge lamp wherein the protective plastic sheath is also employed to hold a pair of lead wires in place on the outer surface of the bulb;

FIG. 4 is an enlarged cross-sectional view along the line IV--IV of FIG. 3;

FIG. 5 is an elevational view of a double-ended discharge lamp having an exterior starting-aid component that is held in place by the plastic sheath;

FIGS. 6 and 7 are elevational views, partly in section, of the basal end portions of jacketed fluorescent lamps embodying the invention; and,

FIGS. 8 and 9 are enlarged cross-sectional views of additional lamp embodiments.

While the invention can be used with advantage in various types of low-pressure gaseous discharge lamps or similar devices to protect the envelopes or attach auxiliary components, it is especially adapted for use in conjunction with fluorescent lamps and it has accordingly been so illustrated and will be so described.

EMBODIMENT I

With specific reference now to the drawing, in FIG. 1 there is shown a fluorescent lamp 10 which has the usual tubular light-transmitting vitreous envelope 12 that is provided with an inner coating 13 of a suitable ultraviolet-responsive phosphor and has stems 14 and 15 sealed into each of its ends. The stems are of conventional construction and include a pair of lead wires which support electrodes 16 and 17, such as tungsten wire coils that are coated with electron-emissive material, at each end of the envelope 12. Suitable base members 18 are secured to the sealed ends of the envelope and carry terminals 20 that are connected to the respective lead wires. The spaced electrodes 16 and 17 are adapted, in conjunction with the usual ionizable fill such as a mixture of neon and argon and a predetermined quantity of mercury, to sustain an electric discharge within the envelope when the lamp is energized.

In accordance with this embodiment of the present invention, the envelope 12 is completely enclosed in a light-transmitting sleeve 22 of heat-shrinkable plastic that is constricted throughout its entire length and, as shown in FIG. 2, forms a smooth tight-fitting sheath that conforms to the configuration of the envelope 12. As will be noted in FIG. 1, the plastic sleeve 22 extends beyond the ends of the envelope 12 and encircles the adjacent body portions of the base members 18. Since the sleeve 22 is constricted throughout its length it is shrunk into tightly fitting and enclosing relationship with the aforesaid portions of the bases 18 as well as the juncture between the bases and the adjacent shoulder of the envelope 12.

The plastic sleeve 22 is preferably fabricated from a heat-shrinkable plastic material such as oriented polyvinyl chloride or a polyolefin, such as polyethylene or polypropylene. Such shrinkable plastics are well known in the art and are oriented or rendered shrinkable by exposure to ionizing irradiation to effect cross-linking between the long molecules of the polymer structure. The plastic is then heated, mechanically expanded or stretched, and cooled while it is in its enlarged form. Upon reheating, the plastic shrinks or returns to its original cross-linked dimensions. A detailed description of such oriented heat-shrinkable plastics is given in U.S. Pat. No. 3,093,448, issued June 11, 1963 to W. C. Kirkpatrick et al.

Any type of durable heat-shrinkable plastic can, of course, also be used, as well as plastics that are so oriented or otherwise structurally modified as to be shrunk by immersion in a chemical bath, etc. The term "oriented plastic" as used herein and in the appended claims means a plastic that has a structure or is so modified as to be rendered shrinkable by subsequent exposure to an activating agency such as heat, a selected chemical or chemical solution, etc.

The shrinkable plastic sleeve 22 is initially of such diameter that it slips freely over the fluorescent lamp 10 and, when activated by heat or other means, shrinks to a diameter such that it forms a skintight sheath. The sleeve 22 is preferably made of monoaxially oriented heat-shrinkable plastic so that only radial shrinkage occurs when it is heated. However, it can also be made from biaxially oriented plastic. Any excess plastic that extends beyond the ends of the base members 18 can be trimmed by a suitable cutting tool after the plastic has cooled. When shrinking the sleeve, care should be taken to prevent overheating the plastic since this may cause excessive shrinkage and splitting of the sleeve.

EMBODIMENT II

In FIG. 3 there is shown an alternative embodiment of the invention wherein a single-ended fluorescent lamp 10a is provided with a shrunk plastic sheath 22a. The lamp 10a includes a tubular envelope 12a which has a closed dome-shaped end and a stem 14a sealed into its opposite end. The second stem 15a is sealed to the domed end of the envelope 12a and supports an electrode 17a at that end of the envelope. The electrode 16a at the basal end of the lamp 10a is connected by suitable lead wires to a pair of terminal pins 24 that protrude from the base member 18a. The other electrode 17a is connected to a second pair of pins 26 by lead wires 19 and 21 that extend through the domed end of the envelope 12a, along its exterior surface and thence into the base member 18a.

The oriented plastic sleeve 22a in accordance with this embodiment is closed at one end and shaped to form a smooth tight-fitting continuous sheath when it is slipped over the lamp 10a and is shrunk into position. The resulting skinlike plastic sheath extends to and covers the adjacent portion of the base member 18a, as shown in FIG. 3, and completely encloses the exposed portions of the lead wires 19 and 21 that extend along the outer surface of the envelope 12a from its closed end to its basal end.

As shown in FIG. 4, the aforesaid lead wires 19 and 21 are interposed between the shrunk plastic sheath 22a and the envelope 12a and are thus permanently locked in spaced-apart relationship and insulated from one another. The lead wires are made as thin as possible, consistent with current-carrying requirements, so as to minimize their masking effect when the lamp is lighted.

EMBODIMENT III

In FIG. 5 there is shown another embodiment wherein a double-ended fluorescent lamp 10b having a tubular envelope 12b containing spaced electrodes 16b and 17b is provided with an electrically conductive member, such as a wire 28, that extends along the outer surface of the envelope from a region proximate one of the electrodes to a region proximate the other electrode and thus serves as a starting aid. The wire 28 aids in establishing the electric discharge within the lamp during starting in the well-known manner and is securely held in place and protected by the shrunk sleeve 22b of plastic that covers the envelope and adjacent portions of the base members.

Other types of starting aids can, of course, be used; for example, a strip of resistive coating material, a printed circuit-type component that is connected to the base pins or the electrodes, etc.

EMBODIMENT IV

In FIG. 6 there is shown one end of a fluorescent lamp 10c embodying another form of the invention. In this embodiment, the envelope 12c is enclosed by a sleeve 22c of oriented plastic that is substantially rigid and of larger diameter than the envelope. Only the end portions E of the sleeve 22c are shrunk down onto the underlying portions of the envelope 12c and base members 18c so that the unconstricted medial portion of the sleeve constitutes a bulbous jacket that protectively encloses substantially the entire lighted length of the envelope. The resulting dead air space S between the bulbous portion of the plastic jacket 22c and the underlying portion of the envelope 12c serves to insulate the lamp and prevents the heat generated by the energized lamp from being dissipated. This particular form of the invention thus provides a very practical and inexpensive "cold weather" fluorescent lamp for outdoor lighting applications.

EMBODIMENT V

A modified "cold weather" fluorescent lamp 10d is illustrated in FIG. 7. According to this embodiment, the protective jacket 30 is made from glass or other vitreous material and constitutes a separate component that is fastened in encircling spaced relationship with the envelope 12d by a pair of short sleeves 32 of oriented plastic that are disposed on the respective ends of the lamp 10d. One end of the lamp 10d and its associated plastic sleeve 32 are shown in FIG. 7. As illustrated, each sleeve 32 overlaps and is shrunk down onto the underlying end of the jacket 30 and onto a suitable spacing member 34 and the adjacent body portion of the base member 18d located at the respective ends of the lamp. The spacing members, as here shown, consist of annular extensions that are secured to the respective base members 18d and encircle and are spaced from the adjoining end of the lamp envelope 12d. Other types of spacer means can be used to support the jacket 30.

The jacket 30 fits snugly over the spacing members 34 and the shrunk plastic sleeves 32 form smooth tight-fitting bands that lock the various components in assembled relationship and provide the desired insulating air space S around the envelope 12d.

EMBODIMENT VI

In FIG. 8 there is shown another embodiment comprising a so-called "aperture" fluorescent lamp 10e having a tubular envelope 12e that is provided with an inner coating 13e of phosphor and is enclosed in a shrunk sleeve 22e of oriented plastic. In accordance with this embodiment a layer 36 of light-reflective material is sealed between the constricted plastic sleeve 22e and the outer surface of the envelope 12e. This reflective material extends along the entire lighted length of the envelope but extends around only part of its circumference so as to provide a slotlike aperture A (see FIG. 8) through which the light rays emerge. The light is thus concentrated into a planar beam of high intensity. Such aperture lamps are employed in photocopy machines and the like where this type of light source is required.

The aforesaid sealed-in layer 36 of reflective material can consist of a slotted tube of metal foil, such as aluminum, or a partial coating of suitable reflective material (such as titanium dioxide, vaporized aluminum or silver, etc.) on the inner surface of the shrunk plastic sleeve 22e or outer surface of the bulb 12e.

EMBODIMENT VII

In FIG. 9 there is shown still another embodiment wherein a fluorescent lamp 10f having a tubular light-transmitting envelope 12f is enclosed in three superimposed sleeves 38, 40 and 42 of oriented plastic that are shrunk into tight-fitting engagement with the envelope and the underlying sleeves. Suitable means such as longitudinally extending fine wires 41 and 43 are sealed between sleeves 38-40 and 40-42 to permit the outermost sleeves to be longitudinally severed and selectively stripped from the lamp. This is accomplished by gripping the exposed ends of the wires and pulling them so that they tear or cut through the plastic.

This particular embodiment thus provides a fluorescent lamp 10f that has a series of tight-fitting plastic sheaths 38, 40 and 42 which can be individually removed as required to provide a clean light-transmitting surface. This is of particular advantage in lighting applications where the lamp is subjected to pitting or hard-to-remove deposits such as weld spatter or the like.

ADDITIONAL EMBODIMENTS

The unique shrink-fit plastic lamp enclosure of the present invention can also be utilized to modify the character of the light produced by the lamp. According to one such embodiment, the shrinkable sleeve is fabricated from a plastic which contains a preselected material that is dispersed within the plastic and absorbs radiations of undesired wavelengths transmitted by the fluorescent lamp envelope. For example, the sleeve is composed of a plastic that contains a substance or material that absorbs ultraviolet (UV) radiation. Such UV-absorbing plastic sheaths would be advantageous in fluorescent lamps that are used in fixtures made of plastic which turns yellow or is otherwise adversely affected by impinging UV radiation, and in lighting applications where fabrics etc., which are affected by UV are being displayed.

According to another embodiment, the oriented plastic sleeve is composed of a resin that polarizes the light as it passes through the sleeve. This shrunk sleeve would thus serve both as a protective enclosure and a polarizing medium and provide a lamp that produces polarized glare-free light without any special fixtures of lenses. A molecular-oriented plastic such as that described in U.S. Pat. No. 3,265,777, issued Aug. 9, 1966 can be employed.

In another embodiment the shrinkable plastic sleeve contains a dispersed fluorescent material that is excited by radiations transmitted by the fluorescent lamp envelope. The fluorescent material can be a phosphor that is excited by UV radiation, or by visible radiations of a preselected wavelength. In the former case, the usual phosphor coating on the inner surface of the bulb can be eliminated, particularly if the bulb is made from UV-transmitting glass. In either case, the radiation absorbed by the plastic sheath will be converted into longer wavelength radiations which will blend with the radiations transmitted by the plastic sheath and thus change the color of the light produced by the lamp. Fluorescent plastic of the type described in U.S. Pat. No. 2,498,593, issued Feb. 21, 1950 to J. L. Switzer, can be used.

Various colored pigments can also be dispersed throughout the shrinkable plastic sleeve so that the latter serves as a filter which modifies the appearance and output of the fluorescent lamp. Various decorative and functional lighting effects (yellow caution lights, etc.,) can thus be readily obtained.

METHOD OF ASSEMBLY

Excellent results have been obtained in the case of 40 watt T-12 48-inch fluorescent lamps by using heat-shrinkable polyvinyl chloride tubing that has an initial diameter of approximately 2 inches, a length of approximately 50 inches and a shrunk diameter of about 11/2 inches. The lamp is inserted into the tubing and centered so that about 11/2 inches of the plastic sleeve extends beyond each of the base faces. The lamp is then supported by the base pins or base faces so that the plastic sleeve is not held or restrained in any way and is thus free to move as it shrinks to fit the lamp.

The lamp is then uniformly heated to a temperature of approximately 400.degree. F. by blowing heated air on the lamp while it is rotated. This can also be achieved by exposing the lamp to radiant heat or by placing it in an oven. When the plastic sleeve has shrunk into tight-fitting engagement with the lamp, the lamp is allowed to cool, during which time contact with the hot plastic is avoided to prevent scratching, etc. After the lamp has cooled, the excess plastic at each end of the lamp is trimmed with a sharp cutting tool.

Tests have shown that fluorescent lamps provided with such shrink-fit plastic sheaths can frequently be dropped from heights of 3 or 4 feet without breaking. Moreover, when the bulb does break the sheath remains intact and preserves the integrity of the lamp. The danger that the force of the resulting implosion of the envelope may scatter glass fragments, lamp parts, dust, etc., is accordingly eliminated. The sheathed lamps are thus admirably adapted for shipboard use and, when fitted with proper bases, can be safely used in lighting applications where an explosive atmosphere is present.

It will be appreciated from the foregoing that the objects of the invention have been achieved in that an inexpensive and practical means has been provided for protectively enclosing and, if desired, modifying the light output of previously fabricated fluorescent lamps and similar devices.

While several embodiments have been illustrated and described, it will be understood that various modifications can be made without departing from the spirit and scope of the invention.

Claims

I claim as my invention:

1. An electric lamp comprising, in combination;

a sealed vitreous envelope containing means for generating visible radiation when the lamp is energized,

a hollow light-transmitting member that is of substantially the same configuration as said envelope and is disposed in protectively enclosing relationship therewith, and

means holding said member in envelope-enclosing position on said lamp comprising a sleeve of oriented plastic material that is attached to said light-transmitting member and encircles a part of said lamp,

said sleeve of oriented plastic material being constricted and in shrink-fitted engagement with the underlying encircled part of said lamp.

2. The electric lamp set forth in claim 1 wherein:

said lamp comprises a tubular fluorescent lamp which contains a pair of spaced electrodes and an ionizable medium, a base member is attached to one end of said envelope, said envelope-enclosing member is of tubular configuration and is composed of light-transmitting oriented plastic material,

said sleeve of oriented plastic material comprises an integral part of said envelope-enclosing plastic member and constitutes therewith a continuous tubular sheath of oriented plastic material, and

said plastic sheath is constricted throughout its entire length and thus comprises a smooth enclosure that conforms to the shape of said envelope and is in shrink-fitted engagement therewith and with the adjacent portion of said base member.

3. The fluorescent lamp set forth in claim 2 wherein;

said base carries a plurality of terminals,

said electrodes are located at the ends of said envelope, the electrode at the based end of said envelope is connected to preselected ones of said terminals by lead wires that extend through the end of said envelope and into said base,

the electrode at the other end of said envelope is connected to preselected and different ones of said terminals by spaced lead wires that extend through the said other end of said envelope and along the outer surface of the envelope into said base, and

the portions of said lead wires that extend along the outer surface of said envelope are interposed between said envelope and the constricted plastic enclosure and are thereby held in spaced-apart insulated relationship by said enclosure.

4. The fluorescent lamp set forth in claim 2 wherein;

an elongated electrically conductive member is disposed on the outer surface of said envelope and extends therealong from a region proximate to one of said electrodes to a region proximate the other of said electrodes, and

said plastic enclosure is in tight-fitting engagement with the portion of said envelope traversed by said electrically conductive member and thus seals said member in place on said envelope.

5. The electric lamp set forth in claim 1 wherein;

said lamp comprises a double-ended fluorescent lamp,

said envelope-enclosing member comprises a substantially rigid tube of oriented plastic material that has a diameter larger than that of said envelope and is held in position on said lamp by a pair of constricted plastic sleeves,

said pair of plastic sleeves are integral parts of and constitute the ends of said plastic tube and are thus in tight-fitting engagement with the underlying parts of said lamp, and

the bulbous intermediate body portion of said plastic tube is spaced from said envelope and thereby also provides an insulating jacket for said lamp.

6. The electric lamp set forth in claim 1 wherein;

said lamp comprises a double-ended fluorescent lamp that has a base member at each end,

said oriented plastic sleeve is located at and encircles one end of said lamp,

a second sleeve of oriented plastic is located at and disposed around the other end of said lamp,

said hollow light-transmitting member comprises a rigid tubular insulating jacket that is larger in cross section than said envelope and is supported in spaced-apart enclosing relationship with said envelope by spacer means attached to the respective base members, and

said oriented plastic sleeves overlap and are in shrink-fitted engagement with the respective ends of said jacket and the adjacent portions of said base members and thus hold said jacket in assembled relationship with said lamp.

7. The fluorescent lamp set forth in claim 2 wherein said oriented plastic sheath is composed of a resin which polarizes the transmitted light rays.

8. The fluorescent lamp set forth in claim 2 wherein said oriented plastic sheath contains a material which absorbs radiation of a preselected wavelength generated by said lamp.

9. The fluorescent lamp set forth in claim 8 wherein the material in said plastic sheath absorbs ultraviolet radiation.

10. The fluorescent lamp set forth in claim 8 wherein said plastic sheath contains dispersed material which absorbs radiation in a preselected portion of the visible spectrum and said sheath thus constitutes a filter that modifies the color of the light emitted by said lamp.

11. The fluorescent lamp set forth in claim 2 wherein said oriented plastic sheath contains fluorescent material that is excited by radiation generated by said lamp and emits visible radiation which modifies the color of the light produced by said lamp.

12. The fluorescent lamp set forth in claim 2 wherein;

said constricted plastic sheath is covered by a second sheath of oriented plastic that is in shrink-fitted overlying relationship therewith, and

means for longitudinally severing said second plastic sheath is sealed therebeneath so that said second sheath can be stripped from the lamp without disturbing or damaging the underlying sheath.

13. The electric lamp set forth in claim 1 wherein;

said envelope-enclosing member is composed of oriented plastic material and together with said oriented plastic sleeve comprises an integral plastic sheath that is constricted and in shrink-fitted engagement with said envelope throughout its length, and

light-reflecting means is interposed between said plastic sheath and said envelope,

said light-reflecting means extending around only a portion of the envelope circumference and being held on and in reflective relationship with said lamp solely by said plastic sheath.

14. As a new article of manufacture, a light-modifying component for an electric lamp or the like comprising a sleeve of shrinkable plastic that contains a dispersed fluorescent material.

15. As a new article of manufacture, a light-modifying component for an electric lamp or the like comprising a sleeve of shrinkable light-polarizing plastic material.

16. As a new article of manufacture, a light-transmitting filter for an electric lamp or the like consisting of a sleeve of shrinkable colored plastic.