GB2475874A

GB2475874A - Festoon lighting

Info

Publication number: GB2475874A
Application number: GB0921194A
Authority: GB
Inventors: Nicholas Graham; Anthony Paul Taylor; Stephen Paul Hainsworth
Original assignee: LIGHTING AND ILLUMINATION TECHNOLOGY EXPERIENCE Ltd
Current assignee: LIGHTING AND ILLUMINATION TECHNOLOGY EXPERIENCE Ltd
Priority date: 2009-12-03
Filing date: 2009-12-03
Publication date: 2011-06-08
Anticipated expiration: 2029-12-03
Also published as: GB2475874B; GB0921194D0

Abstract

A light fitting for festoon lighting has a lamp holder 10 with a connector extension 18 and a translucent lamp housing 20 with a neck 22, connected to the extension 18. The connection is watertight, formed by a push fit taper joint between surfaces of extension 18 and neck 22. In a second invention, a lamp holder 10 has a base 12 with a connector extension 18, and a cap 14. The base 12 and cap 14 have opposing side walls (13,15;23,25, fig 3). The walls of one fit inside the other, forming a channel for a cable. Base 12 and cap 14 have projections (17, 26, fig 3) extending into channel 28, engaging the cable. Side walls (13,15;23,25, fig 3) of base 12 or cap 14 have tapered surfaces forming a push fit connection with opposing surfaces of projections (17,26, fig 3) of cap 14 or base 12 respectively.

Description

I

FESTOON LIGHTING

[0001] This invention relates to improvements in light fittings for festoon lighting.

BACKGROUND

[0002] Festoon lighting, as referred to herein, comprises a length of electric cable to which a plurality of lamp holders are connected at spaced intervals therealong, each lamp holder having fitted thereto, a respective lamp and a lamp housing, which encloses the lamp. Such lighting systems are well-known in the prior art, for example as disclosed in the applicant's own earlier EP-A-0411859 and in GB 2281820 and US 5,562,481 to Luminaire Developments Ltd. [0003] Traditionally, festoon lighting chains were fitted with incandescent lamps. Later, they were redesigned to use lower energy halogen lamps, and currently the requirement is for use of low energy light emitting diodes (LEDs). With the latest generation of LED lamps, a lamp life of 50,000 hours is possible. In view of the cost of installing and dismantling decorative displays, particularly when mounted in trees, it is now standard practice to leave these permanently in place in an outdoor environment and an effective life of 10 years is a commercial requirement.

Accordingly, good weatherproofing measures are essential to maintain trouble-free working life of such festoon lighting.

[0004] Festoon lighting assemblies, namely the cable with lamp holders fitted and with the lamps and their housings installed thereon, and the individual lamp holders are rated against a British standard II' scale for protection against ingress of water and dust. For long life Installations the highest rating, lP68, is called for, requiring a product to withstand immersion in water at a depth of at least I m for a total of four hours without impairment and to satisfy a specified dust ingress test. An additional heat shock test, which may be adopted as a British standard, requires the product to maintain its function after being repeatedly left in an air temperature of 400 C, for 30 minutes followed by immersion in water at a temperature of 2 C. for 30 minutes, the latter being to show that it can withstand more extreme conditions than may be found in waterfront locations in some tropical zones of the world.

[0005] Traditionally, festoon light fittings have been made water and dust tight by means of screw thread clamping and/or 0 ring seals, glands or washers, between the lamp holder and housing. Screw thread clamping requires expensive moulding tools for configuration of the pads while 0 ring seals, glands or washers obviously involve additional components and assembly costs, as well as the risk of omission or loss during subsequent servicing. The requirements of the above British standard up to the highest 1P68 are rarely met by these types of fittings, and where they are there are cost implications and also impaired optical performance owing to the requirements of the lamp housing.

[00061 As regards the lamp housing, when it is necessary to avoid ingress of water or dust, this has been provided as a one-piece blow moulded article, to avoid any joints between parts which could allow such ingress. Such housing is usually in the form of a substantially spherical enclosure with a neck for connection purposes and referred to as " a globe". With such a one-piece moulding it is not possible to provide any internal surface contouring to the housing which in respect of other two part housings may be used to maxirnise light output by refraction I diffraction I magnification. Furthermore, in order to safeguard the LED lamps against any moisture ingress, these LEDs have hitherto been encapsulated in an opaque material, which reduces light output.

(0007] An object of the present invention is to provide components for festoon lighting which will meet the exacting standards mentioned above.

BRIEF SUMMARY OF THE DISCLOSURE

[0008] In accordance with a first aspect, the present invention provides a light fitting for festoon lighting, said fitting comprising a lamp holder and a translucent lamp housing, the holder having a connector extension and the housing having a substantially cylindrical neck portion which is connected to the extension, said connection being achieved in watertight manner by means of a push fit taper joint directly between respective contact surfaces of the holder extension and the housing neck portion, In this way, a watertight joint can be achieved without the use of any additional sealing means, such as washer, gland, 0-ring, or any additional sealing material or compound. Accordingly, this simplifies assembly of the festoon light fitting and greatly increases the reliability of the watertight and dust tight seal which is achieved between the lamp holder and lamp housing. Indeed, in accordance with this aspect of the invention light fittings which comply with the additional heat shock test mentioned above as well as British standard lP68 can be produced.

[0009] In preferred embodiments of the invention, the lamp holder extension fits inside the cylindrical neck portion of the housing to form the watertight joint. However, in other embodiments the arrangement may be the opposite way around, in that that the cylindrical neck portion of the housing fits inside the lamp holder extension. This does not affect the efficacy of the watertight push fit taper joint between respective contact surfaces of these parts.

(0010] Preferably, both the contact surface of the lamp holder and the contact surface of the substantially cylindrical neck portion of the housing are tapered to a matching degree.

However, the respective contact surfaces may be tapered to slightly different angle of inclusion, or one only may be tapered.

[0011] The preferred angle of inclination (taper) is from 1.50 to 30 Accordingly, when considering the substantially cylindrical neck portion of the housing, or conversely the matching substantially cylindrical extension of the lamp holder, across a diagonal, there will be such a taper at each opposing side, namely around the entire substantially circular periphery. A more preferred angle of taper is close to 2°. In this respect, the taper joint has to withstand physical handling during installation of the festoon lighting and expansion of trapped air during its lengthy period of use. If the taper angle is too great there is a risk that the lamp housing may detach from the lamp holder. On the other hand, if the taper angle is too small, there can be problems associated with assembly of the light fitting and the risk of water ingress due to capillary action.

[0012] A particular advantage of this design is the avoidance of any other additional sealing means or compound. This simplifies manufacture and assembly, hence reducing cost, and improving quality control. It also avoid the risk of loss or omission of seals during servicing of the light fittings after installation in the field.

[0013] Another advantage is that it allows for the lamp holder and the lamp housing to be formed of the same material, thus having the same coefficient of expansion and contraction and consequently maintaining the watertight and dust tight joint over a very wide range of temperature and humidity. This is unlikely to be the case when additional sealing materials are present as these generally have a different coefficient of expansion to that of the lamp holder and the lamp housing.

(0014] Yet anotther advantage of this design is that it enables use of an un-encapsulated LED because the lamp housing is reliably watertight, and this in turn means greater light output.

[00153 An additional measure to maximise output of light is to manufacture the lamp housing or globe from two parts, which are independently moulded, with one or both having internal formations of prismatic effect to enhance output of light, these two parts then being hermetically sealed, which can be accomplished by ultrasonic welding.

[0016] A conventional lamp holder for festoon lighting comprises a base, having aforesaid connector extension for attachment of both a lamp and a lamp housing, and a cap which fits onto the base to trap the cable there between. In this respect, the base and the cap are configured and interconnected to define a channel through which the cable is to be laid and the base also includes electrically conductive connectors for the lamp, said connectors having prongs extending into the channel for piercing the cable to make an electrical connection there to. Various ways of making a secure interconnection between the cap and the base have been proposed, as for example in the above-mentioned EP-A-0411859 and US 5,562,481.

[0017] Yet another development in accordance with the present invention, where the base and the cap each have opposing side walls to define the channel and a series of projections extending into the channel for engagement with the cable, is that the side walls of the base fit inside the respective side walls of the cap and the side walls of the base have internal surfaces which are tapered to provide a push fit clamping connection with opposing surfaces of the projections of the cap, which may have a matching taper. Conversely, in other embodiments the side walls of the cap may fit inside the opposing side walls of the base, in which case the side walls of the cap wiU have internal surfaces which are tapered to provide a push fit clamping connection with opposing surfaces of the projections of the base, which may have a matching taper.

(0018] In either arrangement, the base and the cap of the lamp holder are advantageously additionally ultrasonically welded to each other, for example by the side walls of the base or of the cap, respectively, being welded to the other part in the vicinity of the tapered internal surfaces of said walls and of the projections of the other part. This produces a highly reliable watertight joint between the cap and the base of the lamp holder, sufficient to meet British standard IP 68, because the cable is clamped laterally by the taper joint and the welding connection is preferably in a direction substantially perpendicular to the direction of that clamping.

[0019] The aforesaid features relating to the connection between the cap and the base of the lamp holder may be employed independently of the features relating to the connection between the lamp housing and the lamp holder. Accordingly, a lamp hoJder having aforesaid features is a second aspect of the present invention.

BRIEF DECSCRIPTION OF DRAWINGS

(00201 The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section of a preferred practical embodiment of a light fitting in accordance with the first aspect of the invention, the lamp housing being shown separated from the lamp holder; Figure 2 is an enlarged view of the lamp holder shown in figure 1, which is also, in its own right, an embodiment of a second aspect of the present invention; Figure 3 corresponds to figure 2 but shows the cap and the base of the lamp holder separate, prior to their connection; Figure 4 is an end view of the lamp holder of figure 2; Figure 5 is a top plan view of the lamp holder of figure 2; and Figure 6 is a side view of the lamp holder of figures 2 to 5.

S

DETAILED DESCRIPTION

(0021] Referring to figure 1, a preferred practical embodiment of a light fitting for festoon lighting in accordance with a first aspect of the present invention comprises a lamp holder, designated generally by reference numeral 10, and a translucent lamp housing 20.

[0022] The housing 20 is in the form of a hollow sphere having a substantially cylindrical neck portion 22, and it is commonly referred to as "a globe". It is formed of substantially transparent plastics material, typically a polycarbonate, and is fabricated by injection moulding two semi-spherical parts, 20a and 20b, one of which includes the neck portion 22. Internally, these parts 20a and 20b are each formed with a series of annular steps 24 which act as prisms in refracting light from a light source internal to the globe, namely an LED (not shown) fitted to the lamp holder. This achieves significantly greater light output than having a substantially smooth inner surface to the globe 20, which is all that is possible when a festoon lighting globe is formed in one piece (by blow moulding) to avoid any possibility of water ingress. In the present case the two parts 20a and 20b are hermetically sealed in a reliable watertight manner by suitable tongue and groove interconnection (at 21) along with ultrasonic welding.

(0023] The lamp holder 10 comprises a base 12 and a cap 14. as best shown in figure 3, and figures 4 to 6. The base 12 comprises a web portion 16, which is substantially rectangular, save for a part-circular bulge 16a mid way along each longer side, as shown in figure 5, a pair of upstanding side walls 13, 15 projecting at one side of the web portion 16 and a cylindrical connector extension 18 projecting at the opposite side of the web portion 16. Thus the central enlarged region of the bulge iSa overhangs the extension portion 18. As shown in figures Sand 6 in conjunction with figures 2 to 4, the cap 14 of the lamp holder 10 comprises a substantially rectangular plate which also has opposing side walls 23, 25. The side walls 23, 25 of the cap 14 are adapted to fit onto the base 12, outside the side walls 13, 15 to define a channel 28 through which a cable (not shown) is to be laid. In use, the LED lamp (not shown) is mounted centrally into the connector extension 18 and the neck portion 22 of the globe 20 is then fitted onto the exterior of the connector extension 18.

[00241 This connection between the neck 22 of the globe 20 and the connector extension 18 of the lamp holder 10 is achieved in a watertight manner by means of a push fit taper joint between the external surface of the connector extension 18 and the internal surface of the neck portion 22. A preferred angle of inclination (taper) is from 1.50 to 3°, most preferably close to 2°. Preferably, both surfaces are tapered to a matching extent. In the illustrated embodiment the connector extension 18 has a main section 18a adjacent the web portion 16 leading, via an annular shoulder 19 to an end section lOb of narrower diameter. It is the cylindrical periphery of the main section 1 8a of the connector extension 18 which decreases from the web portion 16 to the shoulder 19 through an angle of approximately 20 all around. Thus, across a diameter, the angle of taper is approximately 2° at each side relative to an imaginary line perpendicular to the surface of the web portion 16. This angle is too small to represent on the drawings.

Similarly, the neck portion 22 of the globe 20 decreases in its internal diameter from its outer edge to adjacent the spherical surface through an angle of approximately 2° all around.

[0025] The numerous advantages of such a reliable push fit interconnection have already been explained in the introduction above. No other means of sealing or adhesion are employed.

[0026] The lamp holder base 12, the lamp holder 14 and the lamp housing (globe) 20 are preferably formed of the same non-hygroscopic polymer resin material, typically a polycarbonate material, thus having the same coefficient of expansion.

[0027] In order reliably to achieve the desired watertight push fit interconnection, the moulding tools used for the lamp holder base 12 and the globe portion 20a may advantageously be blasted with fine grit to achieve a textured finish, which may have a depth of about 2 to 3 p, at least on the respective regions for moulding of the connection extension 18 and the neck 22.

The moulded parts themselves will have somewhat lesser depth to the textured finish.

Alternatively, the moulding tools may be textured by fine secondary machining, spark erosion, chemical etching, or vapour blasting.

[0028] The lamp holder 10, as shown in figures 2 to 5, is also a preferred practical embodiment of a second aspect of the invention. The base 12 of the holder 10 has a series of spaced apart projecting walls 17, each having a curving, recessed free edge, extending transversely of the web portion 16, between the respective side walls 13, 15, for the purposes of engagement with the cable (not shown) in the channel 28. The cap 14 is formed with a pair of recesses 27, 29, extending longitudinally of its rectangular plate inwardly of each opposing side wall 23, 25 of the cap 14. The cap also has a series of spaced apart projecting walls 26, each having a curving, recessed free edge, and extending transversely of the cap 14 between these recesses 27, 29. As is apparent by reference to figures 2 and 3, when the lamp holder is assembled, the side walls 13, 15, of the base 12 not only fit snugly inside the side walls 23, 25 of the cap 14 but also project into the aforesaid recesses 27, 29 to define the channel 28 into which the cable (not shown) will have been placed prior to fitting of the cap 14, as is conventional in assembly of festoon lighting. The transverse walls 17 of the base 12 are slightly offset in position compared to the transverse walls 28 of the cap 14 so that side edge margins of these walls 17, 26 fit between each other when the cap 14 is fully pressed into position, as indicated in figure 2.

(0029] The side walls 13, 15 of the bass 12 have internal surfaces which are tapered to provide a push fit clamping connection with opposing surfaces, effectively the side edges, of the transverse walls 26 of the cap 14. Once the side walls 13, 15 have been fully pressed home into the recesses 27, 29, an additional ultrasonic welding operation is preferably undertaken in a vertical direction as viewed in figure 2 so as to weld the upper ends 33, 35, of the side walls 13, 15 to the base of the recesses 27, 29. Together with the extremely secure lateral clamping achieved between the side walls 13, 15 and the projections 28, this results in an exceedingly reliable watertight connection between the cap and the base of the lamp holder 10.

[0030] The aspects of the invention are not restricted to the details of the foregoing embodiment. It has already been mentioned in the introduction that the neck 22 of the globe 20 could alternatively fit inside the connector extension 18 in other embodiments of the fitting. It has also been mentioned that the base and the cap of the lamp holder could be configured differently in other embodiments such that side walls of the cap have the respective inner tapr and fit inside the side walls of the base in order to make a tape of fit with opposing surfaces of transverse walls in the base. Other differences in detailed configuration of the base and cap are possible within the scope of this invention as will be evident to a person skilled in the art.

[0031] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other components. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

(0032] Features described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

Claims

C LA! MS 1. A light fitting for festoon lighting, said fitting comprising a lamp holder and a translucent lamp housing, the holder having a connector extension and the housing having a substantially cylindrical neck portion which is connected to the extension, said connection being achieved in watertight manner by means of a push fit taper joint directly between respective contact surfaces of the holder extension and the housing neck portion.
2. A light fitting according to claim I wherein the lamp holder extension fits inside the cylindrical neck portion of the housing to form the watertight joint.
3. A light fitting according to claim 1 or 2 wherein the contact surface of the lamp holder is tapered at an angle of from 1.5 to 3°.
4. A light fitting according to claim 1, 2 or 3 wherein the contact surface of the substantially cylindrical neck portion of the housing is tapered at an angle of from 1.5 to 3°.
5. A light fitting according to any preceding claim wherein the lamp holder and the lamp housing are formed of the same material.
6. A light fitting according to any preceding claim wherein the lamp holder and the lamp housing are both formed of a non-hygroscopic polymer resin material.
7. A light fitting according to claim 6 wherein the lamp holder and the lamp housing are both formed of the same non-hygroscopic polymer resin material.
8. A light fitting according to any preceding claim wherein the contact surface of the lamp holder and/or of the lamp housing are vapour blasted to achieve a surface texture for watertight contact.
9. A light fitting according to any preceding claim wherein the lamp housing is formed from two parts which are connected by a hermetic seal, at least one of said parts having internal formations to maximise transmission of light from a lamp mounted to the holder, inside the housing.
10. A light fitting according to any preceding claim, further comprising a lamp mounted to the holder, inside the housing, said lamp being an un-encapsulated light emitting diode (LED).
11. A light fitting according to any preceding claim wherein the lamp holder comprises a base, having aforesaid connector extension, and a cap, the base and the cap each having opposing side walls, the walls of the base fitting inside the walls of the cap to define a channel extending between the base and the cap through which a cable is to be laid, and the base and the cap each having a series of projections extending into the channel for engagement with the cable, the opposing side walls of the base having internal surfaces which are tapered to provide a push fit clamping connection with opposing surfaces of the projections of the cap.
12. A light fitting according to any of claims Ito 10 wherein the lamp holder comprises a base, having aforesaid connector extension, and a cap, the base and the cap each having opposing side walls, the walls of the cap fitting inside the walls of the base to define a channel extending between the base and the cap through which a cable is to be laid, and the base and the cap each having a series of projections extending into the channel for engagement with the cable, the opposing side walls of the cap having internal surfaces which are tapered to provide a push fit clamping connection with opposing surfaces of the projections of the base.
13. A light fitting according to claim 11 or 12 wherein the base and the cap of the lamp holder are additionally ultrasonically welded to each other so that the tapered internal surfaces of the walls of the base or the cap, respectively, are welded to the other part in the vicinity of the projections of the other part.
14. A lamp holder for festoon lighting comprising a base, having a connector extension to which a translucent lamp holder is to be fitted in use, and a cap, the base and the cap each having opposing side walls, the walls of the base fitting inside the walls of the cap to define a channel extending between the base and the cap through which a cable is to be laid, and the base and the cap each having a series of projections extending into the channel for engagement with the cable, the opposing side walls of the base having internal surfaces which are tapered to provide a push fit clamping connection with opposing surfaces of the projections of the cap.
15. A lamp holder for festoon lighting comprising a base, having a connector extension to which a translucent lamp holder is to be fitted in use, and a cap, the base and the cap each having opposing side walls, the walls of the cap fitting inside the walls of the base to define a channel extending between the base and the cap through which a cable is to be laid, and the base and the cap each having a series of projections extending into the channel for engagement with the cable, the opposing side walls of the cap having internal surfaces which are tapered to provide a push fit clamping connection with opposing surfaces of the projections of the base.
16. A lamp holder according to claim 13 or 14 wherein the base and the cap are additionally ultrasonically welded to each other so that the tapered internal surfaces of the walls of the base or the cap, respectively, are welded to the other part in the vicinity of the projections of the other part.
17. A light fitting for festoon lighting substantially as hereinbefore described with reference to and as illustrated by figure 1 of the accompanying drawings.
18. A lamp holder for festoon lighting substantially as hereinbefore described with reference to and as illustrated by figures 2 to 6 of the accompanying drawings.