WO1999046800A1

WO1999046800A1 - Black-light blue fluorescent lamp

Info

Publication number: WO1999046800A1
Application number: PCT/IB1998/000810
Authority: WO
Inventors: Michael F. Sica
Original assignee: Sica Michael F
Priority date: 1998-03-10
Filing date: 1998-05-25
Publication date: 1999-09-16
Also published as: AU7228898A

Abstract

Black-light blue fluorescent lamp assemblies (26), in accordance with the present invention, comprise a black-light fluorescent lamp (10) with a glass tube (12) as well as two terminal caps (14) and a tube (16) of a semi-rigid, spectrally selective polymeric material that is coextensive with the glass tube (12) of the lamp (10) and is securely fastened to the terminal caps (14) of the fluorescent lamp (10) are disclosed as well as methods for their manufacture. The lamp may be any commercially available BL fluorescent lamp and thus includes an elongated glass tube (12) and a metal terminal cap (14) at each end of the glass tube, each cap having a flange portion (14a) adjacent the glass tube (12). The polymeric material of the tube (16) that covers the BL fluorescent lamp is formulated, such as by incorporating selected resins, to spectrally select light from the BL lamp in the spectral range of wavelengths of from about 300 nm (namometers) to about 400 nm and to filter out light of wavelengths greater than about 400 nm.

Description

BLACK-LIGHT BLUE FLUORESCENT LAMP

Black-light fluorescent lamps (usually designated BL lamps) , lamps that emit light that is predominantly in the ultraviolet (UV) region of the spectrum, are widely used in various settings, such as disco halls and theaters, for special effects. BL lamps emit not only UV light but some light in the visible region of the spectrum as well. Black-light blue fluorescent lamps (BL-B lamps) emit very little, if any, visible light in the longer range of wavelengths of the visible region of the light spectrum and are produced by adding a colored glass tube to a BL lamp. Conventional BL-B lamps are relatively costly.

An object of the present invention is to provide a lamp similar to a conventional BL-B lamp as far as light quality is concerned but at a much lower cost.

The above object is solved by the combination of features of the independent claim, the dependent claims disclose further advantageous embodiments of the invention.

The following summary of the invention does not necessarily describe all necessary features so that the invention may also reside in a sub-combination of these described features. The foregoing object is attained, in accordance with the present invention, by a lamp assembly that includes a black-light fluorescent lamp and a tube of a semi-rigid, spectrally selective polymeric material that is coextensive with the glass tube of the lamp and is securely fastened to the terminal caps of the fluorescent lamp. The lamp may be any commercially available BL fluorescent lamp and thus includes an elongated glass tube and a metal terminal cap at - 2 -

each end of the glass tube, each cap having a flange portion adjacent the glass tube. The polymeric material of the tube that covers the BL fluorescent lamp is formulated, such as by incorporating selected resins, to spectrally select light from the BL lamp in the spectral range of wavelengths of from about 300 nm (nanometers) to about 400 nm and to filter out light of wavelengths greater than about 400 nm.

The following examples do not limit the claimed inven- tion as they discuss combinations of features which might not be absolutely necessary for the inventive solution .In preferred embodiments of the invention, the polymeric material of the tube is a polycarbonate, and the tube has a wall thickness of about 0.04 cm (about 0.015 inch) . The tube is secured to the caps of the BL fluorescent lamp in a manner to provide a hermetic seal between the caps of the BL fluorescent lamp and the tube.

Lamps according to the present invention may be pro- duced, from a structural point of view, in accordance with the teachings of the following patents, which are owned by the assignee of the present invention:

(1) US Patent application Serial No. 08/620,506, filed March 22, 1996, and entitled FLUORESCENT LAMP WITH A

PROTECTIVE ASSEMBLY [to be issued as US Patent No. 5,729,085 on March 17, 1998].

(2) US Patent No. 5,536,998, issued July 16, 1996, and enti- tied FLUORESCENT LAMP WITH PROTECTIVE ASSEMBLY.

(3) US Patent No. 5,173,637, issued December 22, 1992 and entitled FLUORESCENT LAMP WITH PROTECTIVE ASSEMBLY.

The aforementioned patents are hereby incorporated into the present specification for all purposes. - 3 -

For a more complete understanding of the present invention, and the advantages thereof, reference may be made to the following written description of exemplary embodiments, taken in conjunction with the accompanying drawings, in which:

Fig. 1 shows a partial side cross-sectional view of a first embodiment;

Fig. 2 shows a partial side cross-sectional view of a second embodiment; and

Fig. 3 shows a partial side cross-sectional view of a third embodiment.

In all Figures, reference numeral 10 designates a conventional commercially available fluorescent lamp of the type having an elongated glass tube 12 that necks down slightly at each end and is closed at each end by a cup-like terminal cap 14 having a peripheral flange portion 14a or 14b respectively. The lamp bases may be of conventional bi- pin (as shown), single pin or recessed double contact type. The protective assembly 26 consists of a protective tube 16 preformed from a semi-rigid non-frangible transparent poly- meric material that is received over the glass tube with a slight clearance „C between the outer surface of the glass tube 12 and the inner surface of the protective tube 16 and extends lengthwise substantially coextensively with the glass tube and both terminal caps. The clearance or gap C between the lamp tube and the protective tube 16 should be kept small so as to maintain heat transfer from the lamp through the protective tube to the environment. The small clearance gap C is provided only for the purpose of permitting the lamp to be easily inserted into the protective tube when the protective assembly 26 is installed on the lamp 10. - 4 -

The first embodiment (see Fig. 1), from a structural point of view, is described and shown in US Patent application Serial No. 08/620,506, filed March 22, 1996, and entitled FLUORESCENT LAMP WITH A PROTECTIVE ASSEMBLY [to be is- sued as US Patent No. 5,729,085 on March 17, 1998]. In this specific example of the invention, as applied to a 3.81 cm (1.50 inch) fluorescent tube, the protective tube 16 is a piece cut to length such as to extend lengthwise over the entire lamp tube and terminal caps, (but not over the pro- truding contact pins) from a circular cylindrical tubular extrusion of a polycarbonate resin that is highly stabilized against ultra-violet radiation. The protective tube may be clear or translucent and in either case may by colored or otherwise treated to provide light of the desired character- istics. A suitable clear polycarbonate tubing may be extruded from a resin supplied by Miles, Incorporated, as Resin No. 3207-1112M50. The protective tube has a wall- thickness of about 0.04 cm (about 0.015 inch), an inside diameter of about 3.85 cm (about 1.517 inch) and an outside diameter of about 3.93 cm (about 1.547 inch). Therefore, on the radius, the clearance of gap C between the outside of the glass tube and the inside of the protective tube is about 0.02 cm (about 0.0085 inch). That clearance permits the lamp to be slid easily into the protective tube when the protective assembly 26 is installed on the lamp 10.

The protective assembly 26 is assembled on the lamp 10 by first forming an adhesive layer 18 on each cap flange portion 14a. Any adhesive that forms a durable bond between the respective terminal cap flange and the protective tube and that is resistant to heat may be used. Advantageously, the adhesive layer is provided by a double-faced tape composed of a substrate having a coating of a contact adhesive on each face. A double-faced tape has the advantages of be- ing easy to apply, avoiding the presence of a liquid or paste substance which can be spilled or misapplied, and of providing the adhesive exactly where it is desired without gaps and without extending to areas where it is not beneficial. A contact adhesive also bonds upon contact, requiring no setting or curing. A suitable double-face tape with a contact adhesive suitable for the protective assembly 26 is available commercially from 3M Corporation as No. 4693.

A necked-down closure portion 16a is formed on each end of the protective tube 16 that brings the end portion into engagement with the adhesive layer 18 such as to form an adhesive bond, a moisture barrier and a hermetic seal between each terminal cap of the lamp and the protective tube, the closure portion is formed, in particular, by mechanically and thermally deforming the end portions of the protective tube permanently to engage the adhesive layer 18. The mechanical and thermal deformation of each end portion of the protective tube is produced by the use of tooling (not shown) that includes a circular array of radially movable forming tools, each of which is heated, such as by an elec- trical heating element connected by leads to a power source. The end portion of the protective tube 16, with the lamp 10 installed, is engaged by the forming tools for a time sufficient to heat the end portion to a temperature above the softening point of the polymeric material of the protective tube. When the end portion of the protective tube is heated sufficiently to enable it to be deformed, the forming tools are moved substantially radially toward the lamp terminal cap 14a to displace and deform the end portion of the protective tube so as to engage the inner wall of the end por- tion with the adhesive layer 18.

This first embodiment of the present invention provides a protective assembly 26 in which a protective tube of an polymeric material resistant to U-V radiation and discolor- ing mechanically protects the glass lamp tube against impacts and minimizes the chance of it being broken. The end - 6 -

closure portions of the protective tube are mechanically engaged over the necked down parts of the lamp glass tube and adhesively bonded to the respective terminal caps of the lamp. If the protected lamp should break, the protective as- sembly 26 retains the caps 14 and prevents the dispersal of glass fragments and phosphor powders. The protective assembly 26 does not significantly increase the diameter of the lamp 10, thus permitting it to be easily installed in most available fluorescent lamp fixtures. It is relatively inex- pensive to make, using only small lengths of tape and a single protective tube. The cost of the tooling for forming the closure portions of the protective tube is small, when amortized over long periods of use on a per lamp basis. Installing the protective assembly 26 is quick and easy, thus mini- mizing labor costs.

The second embodiment (see Fig. 2), from a structural point of view, is described and shown in US Patent No. 5,173,637, issued December 22, 1992 and entitled FLUORESCENT LAMP WITH PROTECTIVE ASSEMBLY. The assembly includes a protective tube that is preformed from a semi-rigid non- frangible polymeric transparent or translucent material that is stabilized against ultraviolet radiation and is received over the glass tube with its inner surface substantially uniformly spaced apart from the outer surface of the glass tube to form an air space for insulation of the lamp. The protective tube is substantially coextensive with the full diameter portion of the glass tube lengthwise of the lamp. The desired uniform spacing between the lamp tube and the protective tube is established by a spacer ring 28 located adjacent each end of the glass tube and adhesively bonded to the glass tube. Each spacer ring 28 is formed of a semirigid polymeric foam strip material that is resistant to heat and ultraviolet radiation and is a band of substantially uniform rectangular cross-section having a thickness - 7 -

such that an outer surface of the ring forms a sliding fit with an inner surface of the protective tube 16 so that the protective tube can be slid lengthwise onto the lamp 12. The protective tube is securely joined to the lamp 12 by a col- lar 20 at each end of the lamp 12. Each collar 20 has a first portion received over an end portion of the protective tube 16 and a second portion received over the flange portion 14a of the cap 14, is preformed of a heat-shrinkable polymeric material and is heat-shrunk into sealed relation with the protective tube and the cap flange portion 14a. A first adhesive layer 24 is interposed between each collar 20 and the cap flange portion 14a.

The air gap ,,C" between the lamp tube 12 and the pro- tective tube 16 can also provide an insulation layer for restricting heat transfer from the lamp to the ambient air outside the protective cover and for circulation of air for convective distribution of heat along the length of the lamp. The protective tube absorbs impacts and minimizes the possibility of the lamp being broken. Should the lamp 10 break, the shrink fit collars 20, which are joined to the flanges 14a of the lamp terminal caps 14 and the protective tube 16 by an adhesive 24, 22 as well as by mechanically engaging the flanges 14a and the protective tube 16, maintain the integrity of an enclosure, which is composed of the protective tube 16, the collars 20, and the terminal caps 14, for containment of lamp fragments and phosphor powders.

The foam tape spacer ring 28 provides several func- tions. First, it is a spacer for the protective tube 16 from the lamp, in that it establishes the air gap uniformly with respect to the lamp tube 12 at each end. Because the protective tube 16 is substantially rigid, the uniformity of the air gap along the entire length of the lamp is ensured by establishing the gap C at each end. Second, the foam spacer rings 28 provide thermal insulation at the ends of the air - 8 -

gap and prevent cold spots from forming where the protective tube 16 ends. Third, the foam spacer rings 28 provide impact-absorbing cushions between the protective tube 16 and the lamp tube 12, this reducing the possibility of impacts to the tube, especially near the ends, causing the lamp to fracture. The spacer rings 28 are joined to the lamp tube by an adhesive 28a, thus ensuring that they will stay in place, not only when the protective tube 16 is slid over the lamp when the protective assembly 26 is installed on the lamp 10 but throughout the life of the lamp. The fit between the spacer ring 28 and the protective tube 16 is a „snug fit" in order to enhance the insulation function but to avoid stressing the lamp 10 with the spacer rings 28 already in place. Because the ring 28 is a compressible foam, slight compression is possible without making it difficult to slide the protective tube 16 over the lamp 10.

In this second embodiment, each spacer ring 28 is formed of a silicon foam tape, preferably a silicon foam having a compression deflection of from about 6 to about

96' 527 Nm^-2 (about 14 psi) for 25 % compression (ASTM D1056) , and has a thickness of not less than about 0.24 cm (about 3/32 inch) , which is the minimum desired thickness of the air gap C between the lamp tube 12 and the protective tube 16. The edge of each spacer ring 28 nearest to the terminal cap 14 of the lamp 10 is, preferably, substantially flush with an end of the protective tube 16 and is also axially substantially coincident with the end of the full diameter portion of the lamp tube 12, before it necks down. A suit- able width for each spacer ring 28 is about 1.27 cm (about 0.5 inch), which is a convenient width to handle during assembly and provides desirable thermal insulation and mechanical cushioning effects.

The clearance or gap C between the lamp tube 12 and the protective tube 16 is established and maintained by a spacer - 9 -

ring 28, there being a spacer ring 28 located adjacent each end of the glass tube 12. Each spacer ring is adhesively bonded to the glass tube by an adhesive layer 28a, is formed of a semi-rigid polymeric foam strip material that is resis- tant to heat and ultraviolet radiation, and is in the form of a band of substantially uniform rectangular cross-section and having a thickness such that an outer surface of the ring forms a snugfit with an inner surface of the protective tube so that the protective tube can be slid lengthwise onto the lamp. A collar 20 performed from a heat-shrinkable polymeric material is received in overlapping relation over a portion of the protective sleeve 16 at each end thereof and over the flange portion 14a of the adjacent cap 14. The collar 20 is heat-shrunk into sealed relation with the protec- tive tube 16 and the cap flange portion 14a. A layer 22 of an adhesive is interposed between each collar 20 and the corresponding end of the protective tube 16, and an adhesive layer 24 is interposed between each collar 20 and the corresponding cap flange portion 14a. No adhesive is present be- tween the glass tube 12 of the lamp 10 and the collars 20.

In a specific example of the invention, as applied to a 3.81 cm (1.50 in.) fluorescent tube 10, the protective tube 16 is a piece cut to a length such as to extend lengthwise over the full diameter portion of the lamp tube 12 (but not over the necked-down parts at either end) from an extrusion of a polycarbonate resin that is highly stabilized against ultra-violet radiation. A suitable clear polycarbonate resin is available from Miles, Incorporated, as Resin No. 3207- 1112M50. The protective tube may be clear or translucent and in either case may be colored. The protective tube 16 has a wall-thickness of 0.24 cm (3/32 inch), an inside diameter of 4.6 cm (1 13/16 inch), and an outside diameter of 5.08 cm (2 inch) . Therefore, on the radius, the clearance or gap be- tween the outside of the glass tube 12 and the inside of the protective tube 16 is 0.24 cm (3/32 inch). The clearance C - 10 -

is desirable in that it provides a thermal insulating barrier of air between the glass tube of the lamp and the protective tube that maintains a desirable temperature differential between the lamp tube 12 and the environment outside the protective tube 16. The gap C also allows for flow of convective air currents for maintaining a desirable heat gradient along the length of the lamp.

The spacer rings 28 are strips of silicone rubber foam of substantially uniform, rectangular cross section, having a width of 1.27 cm 17_* inch) and a thickness of 0.24 cm (3/32 inch) . The foam has a compression deflection of from about 6 to about 96' 527 Nm^-2 (about 14 psi) at 25 % compression (ASTM D1056) . It has an acrylic adhesive coating applied to one face and a release liner over the adhesive. To form the ring, a piece of the foam tape is precut form a supply roll to the required length to wrap around the lamp tube 12 and form a snug ball joint where the two ends meet. The tape is applied to the lamp 12 so that its edge nearer the lamp ter- minal cap 14 substantially coincides with the end of the protective tube 16.

The collars 20 are pieces cut to a length of 3.81 cm (1.5 inch) from a tubing product available commercially from 3M, under the designation „FP301". About 1.91 cm (about % inch) of the collar 20 overlaps the protective tube 16. The adhesive 22, 24 is GE PSA and provides additional mechanical retention over and above that provided by shrinking the collar 20 and also provides a moisture barrier and hermetic seal between the lamp 12 and the protection assembly 26.

If the protected lamp breaks, the protective assembly 26 retains the caps and prevents the dispersal of glass fragments and phosphor powders. The protective assembly 26 does not appear to reduce the light transmission, because the protec- tive tube is entirely transparent. - 11 -

The third embodiment, from a structural point of view, is described and shown in US Patent No. 5,536,998, issued July 16, 1996, and entitled FLUORESCENT LAMP WITH PROTECTIVE ASSEMBLY. The protective assembly 26, according to this em- bodiment, consists of a protective tube 16 performed from a semi-rigid non-frangible transparent polymeric material and received over the glass tube 12 with a clearance „C" between the outer surface of the glass tube 12 and the inner surface of the protective tube 16 and extending lengthwise substan- tially coextensively with the glass tube 12 and a collar 20 preformed from a heat-shrinkable polymeric material received in overlapping relation over a portion of the protective sleeve 16 at each end thereof and over the flange portion 14a of the adjacent cap 14. The collar 20 is heat-shrunk into sealed relation with the protective tube 16 and the cap flange portion 14a. A layer 22 of an adhesive is interposed between each collar 20 and the corresponding end of the protective tube 16 and the corresponding cap flange portion 14a. The adhesive layer 22 is not present between the glass tube 12 of the lamp 10 and the collars 20.

In a specific example of the invention, as applied to a 3.81 cm (1.50 in.) diameter fluorescent tube 10, the protective tube 16 is a piece cut to a length such as to extend over the full diameter portion of the lamp tube 12 (but not over the necked-down parts at either end) from an extrusion of a polycarbonate resin that is highly stabilized against ultra-violet radiation. The tubing is available commercially form Thermoplastic Processors, Incorporated, of Sterling, NJ, as Product No. 58UV, which is manufactured from a resin supplied by Mobay, Incorporated (Resin No. 3207-1112M50) . The protective tube has a wall-thickness of 0.04 cm (0.015 in.), an inside diameter of 3.85 cm (1.517 in.) and an outside diameter of 3.93 cm (1.547 in.). Therefore, on the di- ameter, the clearance C between the outside of the glass tube 12 and the inside of the protective tube 16 is 0.04 cm - 12 -

(0.017 in.). The clearance C is desirable in that it provides a thermal insulating barrier between the glass tube and the protective tube that keeps the protective tube from being highly heated. Also, it facilitates assembling the protective tube 16 onto a finished lamp 10. The collars 20 are pieces cut to a length of 3.81 cm (1.5 in.) from a tubing product available commercially from E.H. Canis & Son, Inc., of Metuchen, NJ, under the trademark „Astramelt^λ . About 2.54 cm (1.0 in.) of the collar 20 overlaps the pro- tective tube 16 lengthwise. The adhesive 22 is 3M No. 4693 and provides additional mechanical retention over and above that provided by shrinking the collar 20 and also provides a moisture barrier and hermetic seal between the lamp 10 and the protective assembly 26.

If the protected lamp breaks, the protective assembly 26 retains the caps 14 and prevents the dispersal of glass fragments and phosphor powders. The protective assembly 26 does not appear to reduce the light transmission, because the protective tube 16 is entirely transparent. The protective tube of an experimental assembly according to the above example has shown no tendency to discolor after a year in service .

In each of the three embodiments, the lamp 10 is a conventional BL fluorescent lamp. The tube 16 is of a polycarbonate which is compounded with resins that make it trans- missive to light predominantly in the spectral range of wavelengths from about 300 nm (nanometers) to about 400 nm and to filter out light of wavelengths greater than about 400 nm. Selection of suitable resins is, per se, known to those skilled in the art relating to the spectral characteristics of polymeric materials. A suitable supplier of poly- carbonates compounded to meet light transmissivity specifications requested by its customers is Rohm & Hass. - 13 -

Some advantages of the present invention are:

• A safety fluorescent lamp is provided that may use a standard „room temperature" lamp - designed for about 21 °C (70 °F) ambient temperature - that operates at low ambient temperatures with substantially the same light output as the unprotected lamp operating at normal ambient temperatures. In particular, the protected lamp of the present invention operates efficiently at ambient temperatures as low as -34 °C (-30 °F) .

• A „safety" BL-B fluorescent lamp is provided in which the glass tube or envelope of the fluorescent lamp component is protected from impacts.

• A fluorescent lamp is provided having a very effective protection against scattering of glass fragments from the tube, phosphor powders, and mercury in the environment, in the event that the glass tube of the fluorescent lamp com- ponent is shattered or broken.

• A protected fluorescent lamp is provided in a way that does not reduce the light output during the useful life of the lamp due to discoloration or clouding of the protec- tive element.

Claims

- 14 -Claims

1. Black-light blue fluorescent lamp assembly (26), com- prising a black-light fluorescent lamp (10) with a glass tube (12) as well as two terminal caps (14) and a tube (16) of a semi-rigid, spectrally selective polymeric material that is coextensive with the glass tube (12) of the lamp (10) and is securely fastened to the terminal caps (14) of the fluorescent lamp (10) .

2. Black-light blue fluorescent lamp assembly (26) according to claim 1, characterized in that the fluorescent lamp (10) is a commercially available BL fluorescent lamp having an elongated glass tube (12) and a metal terminal cap (14) at each end of the glass tube, each cap (14) having a flange portion (14a, b) adjacent the glass tube (12) .

3. Black-light blue fluorescent lamp assembly (26) according to claim 1 or 2, characterized in that the polymeric material of the tube (16) that covers the BL fluorescent lamp is formulated, such as by incorporating selected resins, to spectrally select light from the BL lamp in the spectral range of wavelengths of from about 300 nm to about 400 nm.

4. Black-light blue fluorescent lamp assembly (26) according to claim 3, characterized in that the tube (16) is formulated further to filter out light of wavelengths greater than about 400 nm.

5. Black-light blue fluorescent lamp assembly (26) according to any one of claims 1 to 4, characterized in that the tube (16) comprises a necked-down closure portion - 15 -

(16a) which is formed on each end of the protective tube (16) .

6. Black-light blue fluorescent lamp assembly (26) accord- ing to claim 5, characterized in that the necked-down closure portion (16a) of the tube (16) is designed to bring the end portion of the tube (16) into engagement with an adhesive layer (18) applied to peripheral flange potions (14a, b) of the lamp (10) such as to form an ad- hesive bond.

7. Black-light blue fluorescent lamp assembly (26) according to any one of claims 1 to 4, characterized in that a spacer ring (28) is located adjacent each end of the glass tube (12) between the protective tube (16) and the glass tube (12) .

8. Black-light blue fluorescent lamp assembly (26) according to claim 7, characterized in that each spacer ring (28) is adhesively bonded to the glass tube (12) by an adhesive layer (28a) .

9. Black-light blue fluorescent lamp assembly (26) according to claim 7 or 8, characterized in that a collar (20) performed from a heat-shrinkable polymeric material is received in overlapping relation over a portion of the protective sleeve (16) at each end thereof and over the flange portion (14a) of the adjacent cap (14).

10. Black-light blue fluorescent lamp assembly (26) according to claim 9, characterized in that the collar (20) is heat-shrunk into sealed relation with the protective tube (16) and the cap flange portion (14a) . - 16 -

11. Black-light blue fluorescent lamp assembly (26) according to claim 10, characterized in that a layer (22) of an adhesive is interposed between each collar (20) and the corresponding end of the protective tube (16), and an adhesive layer (24) is interposed between each collar (20) and the corresponding cap flange portion (14a) .

12. Black-light blue fluorescent lamp assembly (26) according to any one of claims 1 to 11, characterized in that a clearance (C) between the outer surface of the glass tube (12) and the inner surface of the protective tube (16) is provided, of a polycarbonate resin that is highly stabilized against ultra-violet radiation.

13. Method of manufacturing a black-light blue fluorescent lamp assembly (26) with a black-light fluorescent lamp (10) , a glass tube (12) as well as two terminal caps (14) and a tube (16) of a semi-rigid, spectrally selective polymeric material characterized by the step of forming an adhesive layer (18, 22, 24) on each cap flange portion (14a) ;

14. Method of manufacturing according to claim 13, further comprising the step of sliding a cut to length protec- tive tube (16) over the lamp (10), so that the protective tube (16) extends lengthwise over the entire lamp tube (12) and terminal caps (14) with a clearance or gap (C) between the outside of the glass tube (12) and the inside of the protective tube (16) .

15. Method of manufacturing according to claim 14, further comprising the step of forming an adhesive layer (18, 22, 24) on each cap flange portion (14a) . - 17 -

16. Method of manufacturing according to claim 15, further comprising the step of forming a necked-down closure portion (16a) on each end of the protective tube (16) that brings the end portion into engagement with the ad- hesive layer (18) such as to form an adhesive bond.

17. Method of manufacturing according to any one of claims 13 to 16, characterized in that the adhesive layer (18, 22, 24) is provided by a double-faced tape.

18. Method of manufacturing according to any one of claims 13 to 17, characterized in that forming the necked-down closure portion (16a) is carried out by mechanically thermally deforming the end portions of the protective tube (16) permanently to engage the adhesive layer (18).

19. Method of manufacturing according to claim 13 further comprising the steps of:

ΓÇó forming a spacer ring (28) nearest to the terminal caps (14) of the lamp (10)

ΓÇó sliding a cut to length protective tube (16) lengthwise onto the lamp (12) ;

ΓÇó performing a collar (20) from a heat-shrinkable polymeric material; ΓÇó securely joining the protective tube (16) to the lamp (12) by the collar (20) which is received in overlapping relation over a portion of the protective sleeve (16) at each end thereof and over the flange portion (14a) of the adjacent cap (14) .

20. Method of manufacturing according to claim 19, characterized in that a layer (22) of an adhesive is interposed between each collar (20) and the corresponding end of the protective tube (16), and an adhesive layer (24) is interposed between each collar (20) and the corresponding cap flange portion (14a) . - 18 -

21. Method of manufacturing according to claim 13 further comprising the steps of:

ΓÇó performing a collar 20 from a heat-shrinkable polymeric material;

ΓÇó heat-shrinking the collar (20) into sealed overlapping relation with the protective tube (16) and the cap flange portion (14a) at each end thereof.

22. Method of manufacturing according to claim 21, characterized in that a layer (22) of an adhesive is interposed between each collar (20) and the corresponding end of the protective tube (16) .