US3328578A

US3328578A - Trough-shaped luminaire with housing

Info

Publication number: US3328578A
Application number: US461340A
Authority: US
Inventors: Alfred B Gough
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-06-04
Filing date: 1965-06-04
Publication date: 1967-06-27
Anticipated expiration: 1984-06-27

Description

June 27, 1967 A. B. GOUGH TROUGH-SHAPED LUMINAIRE WITH HOUSING 6 Sheets-Sheet 1 Filed June 4, 1965 June 27, 1967 A B, GOUGH 3,328,578

THOUGH-SHAPED LUMINAIRE WITH HOUSING Filed June 4, 1965 6 SheetsShee 2 June 27, 1967 A. B. GOUG'H TROUGH-SHAPED LUMINAIRE WITH HOUSING 6 Sheets-Sheet 5 Filed June June 27, 1967 GOUGH 3,328,578

THOUGH-SHAPED LUMINAIRE WITH HOUSING Filed June 1965 6 Sheets-Sheet 4 June 27, 1967 GOUGH 3,328,578

TROUGH-SHAPED LUMINAIRE WITH HOUSING Filed June 4, 1965 6 Sheets-Sheet 5 June 27, 1967 B GQUGH THOUGH-SHAPED LUMINAIRE WITH HOUSING 6 Sheets-Sheet 6 Filed June 4, 1965 United States Patent 3,328,578 TROUGH-SHAPED LUMINAIRE WITH HOUSING Alfred B. Gough, Flat Rock, N.C., assignor to General Electric Company, a corporation of New York Filed June 4, 1965, Ser. No. 461,340 Claims. (Cl. 24093) ABSTRACT OF THE DISCLOSURE Tunnel luminaire comprises upper trough-shaped housing closed by a transparent refractor with longitudinal prisms and separably secured along opposite sides to the housing by a plurality of combined latch and hinge means, the joints between the parts being in fluid-tight engagement.

The present invention relates to luminaires, and more particularly to elongated luminaires adapted for lighting tunnels and underpasses.

It is an object of the invention to provide a luminaire of the above type having improved means for latching the refractor to the housing to enable ready access to the interior of the housing for relamping, cleaning and other maintenance operations.

It is another object of the invention to provide a luminaire of the above type having an improved optical system including reflector and refractor structures for effective control of light distribution.

A further object of the invention is to provide improved fluid-tight sealing means at the joints of the luminaire housing and refractor assemblies.

Other objects and advantages will become apparent from the following description and the appended claims.

With the above objects in view, the present invention in one of its aspects relates to a luminaire comprising, in combination, an upper inverted trough-shaped housing having a top and opposite side portions, a lower troughshaped refractor forming a closure for said housing, the housing having first support means projecting inwardly from its opposite side portions, a reflector having opposite sides engaging the first support means and dividing the interior of the enclosed housing-refractor unit into upper and lower compartments, the housing having second support means projecting downwardly from its top, electrical operating components in the upper compartment supported by the second support means, lampholder means for mounting lamp means in the lower compartment, and combined latch and hinge means holding opposite sides of the refractor inv closed, fluid-tight engagement with the housing.

As more fully described below, the refractor is formed with longitudinal prisms on its outer surface to provide uniform dispersion of light from thte luminaire, the refractor being provided with molding strips along its upper edges which securely engage the refractor and provide effective sealing means with the housing.

The invention will be better understood from the following description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view of an embodiment of a tunnel luminaire constructed in accordance with the invention;

FIGURE 2 is an enlarged perspective view in section of a portion of the FIGURE 1 luminaire as viewed along the line 2-2 of FIGURE 1;

FIGURE 3 is a side elevational view, partly broken away, of the FIGURE lluminaire;

FIGURE 4 is a fragmentary end elevational view of the luminaire taken along the line 44 of FIGURE 3;

3,328,578 Patented June 27, 1967 FIGURE 5 is a fragmentary cross-sectional view of the luminaire taken along the line 55 of FIGURE 3;

FIGURE 6 is a fragmentary cross-sectional view of the luminaire taken along the line 6-6 of FIGURE 3;

FIGURE 7 is an enlarged detailed view, partly in section, of the latching and adjacent parts of the luminaire;

FIGURE 7a is a detail view in cross-section of the end wall gasket shown in FIGURE 7;

FIGURE 8 is a fragmentary perspective View partly in section of means supporting a terminal board in the luminaire;

FIGURE 9 is a fragmentary side view of the optical system of the luminaire, including a ray diagram; and

FIGURE 10 is a fragmentary cross-sectional view of the luminaire optical components, including a ray diagram.

Referring now to the drawings, and particularly to FIGURE 1, there is shown a luminaire of a type adapted to be used for lighting tunnels or underpasses and comprising an elongated housing 1 of a metal such as aluminum having an upper hood portion 1a and end walls 112,

1c, and a transparent cover or refractor 2 enclosing the bottom of housing 1 and releasably attached to both sides of the latter by combination hinge-latches 3 spaced along the opposite longitudinal edges of hood 1a.

Brackets

4 and 4 secured at opposite ends of housing I serve to mount the luminaire on a suitable support, such as on the wall or roof of the tunnel or underpass, with the longitudinal axis of the luminaire parallel to the roadway.

In the embodiment shown (see FIGURE 4), each

mounting bracket

4, 4 has an aperture at its lower end fitting loosely over an annular ridge 1 which surrounds a corresponding aperture in the end wall, and an annular clamping plate 5 releasably clamps brackets 4, 4' to the respective end walls in the desired angular position by means of screws 6. The luminaire may thereby be rotatably adjusted about its longitudinal axis to aim it toward the roadway in the optimum angular position. The inner surface defining the apertures in end walls 1!), 1c and in the annular ridges projecting therefrom is formed with screw threads for threadably engaging a tubular conduit 7 for carrying electrical conductors. Alternatively the end wall may be formed with a clearance hole for receiving a threaded conduit tube, and suitable lock nuts and gaskets (not shown) are employed to secure the conduit tube in place with a fluid tight fitting. I

As best seen in the cutaway view of FIGURE 2, an elongated reflector 10, such as a sheet of aluminum, is mounted with its longitudinal edges 10a, 10b engaged in opposite C-

shaped channels

11a, 11b formed on the inner surface of housing 1. These longitudinal reflector edges are provided along limited regions thereof with flared-out portions, as indicated by portion 10d in FIGURE 7, so that when the reflector is snapped into place in

opposite channels

11a, 11b, the flared portions 10d maintain pressure to keep the reflector from vibrating or falling out. Typically, such flared-out portions 10d are provided two to a side and opposite one another, and the removal of the reflector from the housing is readily effected by grasping the sides of the reflector adjacent these portions and compressing the reflector to move its longitudinal edges out of the

retaining channels

11a, 11b. Replacement of the reflector in the housing is achieved in similar fashion.

Reflector 10 is further preferably formed with a bend portion extending centrally along its length, thereby providing two concave reflector portions facing the lamps in the lower compartment for properly distributing the reflected light throughout the transparent refractor 2. Bend 100 also provides for the desire-d degree of resiliency in the aluminum reflector sheet for yieldably retaining its edges in engagement with housing channels 11a, 1112, while still permitting ready removal therefrom by compressing the sides, as described.

Reflector divides the interior of housing 1 into a lower compartment occupied by elongated fluorescent lamps 12 and an upper compartment in which are located electrical components such as ballasts, conductors, terminal boards and associated parts. At each end of the lower compartment (see FIG. 6) a lamp holder plate 15 is secured, e.g., by screws 16, to supporting bosses (not shown) projecting inwardly from

housing end walls

1b, 1c. Each lamp holder plate 15 is provided with sockets 17 for receiving and holding the contact ends of lamps 12..

Each

end wall

1b, 10 comprises a plate member, e.g., of aluminum, secured by screws or the like to hood 1a and having an inwardly projecting continuous ridge (see FIGURE 6) which follows a tortuous path generally along the upper edge portion of the end wall and which has a generally U-shaped form along the lower edge portion to which a resilient gasket 21 is secured on the outward side thereof. The inner surface of hood 1a is formed with

ribs

22 and 22a which are generally complementary to the indentations formed in upper ridge 20 and which in the assembly of the end walls on hood 1a interfit with those indentations. However, sufficient space is left therebetween in which a non-hardening, elastomeric sealing material 23, such as silicone rubber compound, which is capable of withstanding weathering and vibration over a wide temperature range, is introduced to ensure a fluid-tight seal at this joint. As seen in FIGURE 2, longitudinal part-

circular channels

18, 19 and 18', 19' are formed in the inner surface of hood 1a extending along the length theerof. Thread-forming

screws

18a, 19a (see FIGURE 4 and FIGURE 6) serve to hold the end walls on hood 1a by being screwed into the

respective channels

18 and 19.

As shown in the detail view of FIGURE 7a, gasket 21, which is secured to the lower U-shapedportion of ridge 20 is preferably hollow with spaced external ribs and made of a resilient material, such as extruded neoprene rubber or silicone elastomer which is resistant to compression set, so that when refractor 2 is in closed position on housing 1, it bears at its opposite ends on gasket 21 and compresses it to provide a fluid-tight seal at this joint.

As seen in FIGURES 2 and 5, there are located in the upper housing compartment a plurality of cable retainers 25 in the form of strips each having a looped lower end portion 25a and a bent upper end portion 25b, and having an intermediate bend portion which serves to resiliently urge the end portions into engagement with

longitudinal channels

18 and 19 formed in the sides and top of hood 1a. Looped portion 25a is sufficiently large in diameter to be held captive in channel 18 (see FIGURE 7), whereas bent end portion 25b may be removed from channel 19 (see FIGURE 5) simply by compression of strip member 25. Strip members 25 are arranged in spaced positions along the length of hood In on one or both sides thereof, and in this assembly they serve to retain in place the main power supply cables C (see FIGURE 2) strung along the upper corners of the housing when the luminaire is installed.

The roof of hood 1a is formed with dependent L-

shaped projections

26, 27 facing each other and running along the length of the hood, these projections serving as support rails for retaining in position electrical components of the luminaire located in the upper compartment. Cross bars 29 arranged at opposite ends of ballast unit 28 (see FIGURES 3 and 5) rest at their opposite ends on

projections

26 and 27 and are provided with screws 30 threaded therein which bear against end flanges on ballast unit 28, clamping the latter against

ribs

22, 22a on the roof of hood 1a and serving to retain it in fixed position.

Ribs

22, 22a thus also serve as heat transfer means for maintaining ballast 28 at the proper operating temperature.

As shown in FIGURE 8, a pair of superposed

flat cross members

31, 32 secure terminal board 33 in position by clamping

rails

26 and 27 between them at opposite ends by means of screws 34 which pass through a flange on terminal board 33 and are threaded through clamping

cross members

31, 32. Another pair of cross members is similarly arranged at the opposite end of terminal board 33 for securing that end.

In luminaires of relatively short lengths, say 4 ft. or less, reflector 10 extends along the luminaire in one piece. In longer luminaires, such as those made in multiples of 4 ft. lengths, the reflector is made in two or more separate sections. In such cases, it is desirable to provide a tie bar 50 (see FIGURES 5 and 7) extending laterally across housing 1 and arranged between adjacent sections of reflector 10. Tie bar 50 in the embodiment shown comprises main member 50a of U-shaped cross-section (see FIGURE 3) formed with grooves 50b spaced inwardly from opposite ends, and clamp members 51 each having depending inner and outer flanges and separably secured to main member 50a by a screw 52. Each clamp member 51 is arranged with its inner flange fitting into groove 5% and its outer flange in the recess formed behind channel 11a. Main member 50 is notched at its ends to receive the upper portion of channel 11a, so that when tie bar 50 is assembled with clamp 51 and the notched end of member 50a engaging opposite surfaces of the upper portion of chan: nel 11a, screw 52 is tightened, and the other end of, tie bar 50 is similarly secured to channel 11b. In this way, tie bar 50 serves to retain housing 1 in the proper lateral dimensions and stabilize its form, especially in relatively long luminaires.

Refractor 2 of the luminaire is generally trough-shaped and is made of a transparent material, such as a synthetic plastic, e.g., methylmethacrylate, and is formed around its exterior surface with a plurality of prisms extending along its length, as shown in FIGURE 2. On each upper edge of refractor 2 is clamped a metal molding strip 40, such as of aluminum, which, as shown best in the enlarged view of FIGURE 7, has a fiat inner portion 40a, a doubleflanged outer rail portion 40b, and an inwardly facing gripping portion 400 having upper and lower bearing sur faces at an angle to one another and formed to tightly grip the angled faces of the uppermost .prism on refractor 2 when metal molding 40 is clamped alongthe upper edge of the refractor. Molding portion 400 is formed to provide an opening between the molding and the engaged refractor portion in which a sealing material 41, such as a silicone rubber or other oil-soluble elastomer that can withstand salt spray, weathering, vibration and other environmental extremes of temperature, is introduced to provide a fluid-tight seal at this joint when the molding 40 is clamped in place over the edge of refractor 2. The.

remaining opening 42 between molding 40c and the upper edge of refractor 2 is filled at the opposite ends of the refractor with similar sealing material.

Sealing gasket 43, made of sponge rubber or the like, is secured along the underside of rim 1d of the housing which is formed with an outer lip 1e overhanging the gasket seal surface, and forming therewith a protected recess in which gasket 43 is located. When refractor 2 is in assembled position closing the interior of housing 1, the uppermost edge of molding 40 engages and compresses gasket 43 and outer bearing surface 40d of molding 40 comes into mating engagement with the bottom edge of lip 1e of the housing, as seen in FIGURE 2. There are thus provided an outer bearing surface and an inner seal surface bywhich the housing 1 mates with molding 40 on refractor 2, and in the closed position of refractor 2 there is thus afforded on opposite sides of the assembly effective fluid-tight seals between the exte-,

rior and the interior of the housing at these joints.

Refractor 2 is held in tightly closed position by means of hinge-latches 3 which are pivotally attached to housing 1 and which engage hook members 45 secured to refractor molding 40, as seen in FIGURE 7. Each latch assembly 3 comprises a mounting portion 3a fixedly secured to hood la and having spaced outwardly extending flanges, a lever portion 3b secured by pivot pin 30 to the flanges of lever portion 3b for pivoting about an axis parallel to the longitudinal axis of housing 1 and a wire loop member 3d swingably attached to lever portion 31) at aligned apertures therein spaced above and somewhat inwardly of the axis of pivot pin 30, as seen in the locked position of the latch in FIGURE 7. In the fully closed position of refractor 2 as shown in FIGURES 2 and 7, the flanges of fixed mounting portion 3a straddle hook 45, 100p member 3a engages hook 45 and seats in recesses provided at the bottom of the flanges of mounting portion 3a, and lever portion 312 is in the locked upper position after being pressed toward hood 1a until the plane of wire loop member 3d is positioned inwardly of the axis of pivot pin 3c. Such locking is effected by the inherent resiliency of wire loop member 3d, which permits it to be snapped over center, i.e., beyond the axis of pivot 30, while in engagement with latch book 45, and while loop member 3a. resiliently urges the mating parts of refractor 2 and hood 1a described above into fluid-tight sealing engagement with one another.

As seen in FIGURE 7, hood 1a is formed along its length with a channel 1g in which mounting portion 3a 18 slidably received during assembly so that the latter member may be positioned anywhere along the hood and then fixed in the desired position simply by peening or otherwise indenting the web of mounting portion 3a to fixedly secure it in channel 1g and prevent it from sliding therealong. Portion 3:; may alternatively be welded, riveted or otherwise fixed in the desired position in channel 13.

Similarly, hook member 45 slidably engages rail flanges 40b by means shOWn in FIGURE 7 and may be fixed in desired position thereon in the manner described in connection with latch member 3a.

To open latch 3, lever portion 3b is pulled outwardly and downwardly about its pivot axis so that loop member 3:! drops out of engagement with latch hook 45 and the recesses at the bottom of the flanges of mounting portion 3a. When all the latches 3 along one side of the luminaire are so disengaged, refractor 2 is still swingably attached to housing 1 by loop members 3d of the latches along the opposite side of the housing, that is, hook 45 swings about loop member 3d as a hinge, and thus refractor 2 may be swung away from the housing along one side to provide ready access thereto for necessary maintenance and repair.

As seen best in FIGURE 10, the longitudinal external prisms 2a formed on the outside surface of refractor 2 are arranged side by side throughout the entire extent of refractor 2. The inner surface of refractor 2 is formed with a series of convex portions 211 arranged opposite the external prisms and extending along the length thereof. These convex refractor portions serve in combination with external prisms 2a to produce a uniform, glare-free dispersion of light emanating from the luminaire. As seen from the ray diagrams in the cross sectional view of FIGURE 10, the light rays from the adjacent lamp (as well as light reflected by reflector 10) are collected by the internal convex portions 221 and refracted thereby toward the external prisms which distribute the light rays externally. Internal reflection by the inner surface of refractor 2 is thereby substantially reduced. However, as will be seen from the ray diagrams in the fragmentary elevational view of FIGURE 9, those light rays which strike the refractor at relatively great angles in the planes parallel to the length of the luminaire are for the most part either reflected internally or refracted by the external prisms to emanate at angles which do not cause glare to oncoming motorists.

There is thus provided in accordance with. the invention, a luminaire structure which is readily mounted and adjusted for use in illuminating tunnels and underpasses,v

which is weatherproof and rugged in construction, which is readily opened for access to the interior for maintenance and repair, and which provides uniform illumination of the tunnel areas while avoiding glare for oncoming motorists, as well as other advantages.

While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as come within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a luminaire, an elongated inverted trough-shaped housing having opposite end walls closing the opposite ends thereof, each end wall being formed along its inner surface adjacent the upper edge thereof with a continuous ridge extending transversely of said housing in a tortuous path, the underside of said housing having downwardly projecting ribs formed therein, the end portions of which are received in recesses formed in said ridge, and yieldable sealing means occupying the remainder of said recesses for fluid-tightly sealing the joints between said housing and said end walls thereof.

2. In a luminaire, an elongated inverted trough-shaped housing having opposite end walls closingthe opposite ends thereof, each end wall being formed along its inner surface adjacent the upper edge thereof with a continuous ridge extending in a tortuous path, said housing having projecting ribs formed therein, the end portions of which are received in recesses formed in said ridge, yieldable sealing means occupying the remainder of said recesses for fluid-tightly sealing the joints between said housing and said end walls thereof, each said end wall having a projecting lip forming a U-shaped continuation of said ridge and extending along and spaced inwardly from the lower edge of said end wall, resilient gasket means secured to said projecting li a trough-shaped refractor forming a closure for said housing and engaging said gasket means at opposite ends in sealing relation therewith, and latch means holding said refractor in closed, fluid-tight sealing relation with said housing.

3. A lighting fixture comprising, in combination, an upper inverted trough-shaped housing having a top and opposite side portions, 3. lower trough-shaped refractor forming a closure for said housing, said housing having first support means projecting inwardly from its opposite side portions, a reflector having opposite sides engaging said first support means and dividing the interior of the enclosed housing-refractor unit into upper and lower compartrnents, said housing having second support means comprrsmg spaced elongated ribs of L-shaped cross section facing each other and depending from said top of said housing, a plurality of cross members extendingbetween and supported at their ends by said spaced depending ribs, electrical operating components in said upper compartment secured to and supported by said cross members, lamp holder means for holding lamp means in said lower compartment, and combined latch and hinge means holdrng said refractor in closed, fluid-tight engagement with said housing.

4. A lighting fixture comprising, in combination, an upper inverted trough-shaped housing having a top and opposite side portions, a lower trough-shaped refractor forming a closure for said housing, said housing having first support means projecting inwardly from its opposite side portions, a reflector having opposite sides engaging said first support means and dividing the interior of the enclosed housing-refractor unit into upper and lower compartments, said housing having second support means projecting downwardly from its top, electrical operating components in said upper compartment supported by said second support means, lamp holder means for holding lamp means in said lower compartment, combined latch and hinge means holding said refractor in closed, fluid-tight engagement with said housing, and a plurality of spaced elongated resilient members extending between and engaged at their ends respectively at said first and second support means for retaining electrical conductors in said upper compartment.

5. In a luminaire, an upper inverted trough-shaped housing, a lower trough-shaped refractor forming a closure for said housing, molding strip means embracing and extending along the. opposite upper edges of said refractor, said molding strip means and said housing each having outer bearing surfaces and inner sealing surfaces mating with each other in closed assembly, gasket means between said mating inner sealing surfaces, and combined latch and hinge means holding said refractor in closed, fluid-tight engagement with said housing, and comprising a base member secured to said housing adjacent the bearing surfaces thereof and having spaced outwardly projecting flange portions, a lever member pivoted at one end to said flange portions, a wire loop member swingably secured to said lever member, and a hook member fixed to said molding strip means of said refractor, said wire loop being engageable with said hook member, and said lever member being movable about its pivot axis toward said housing for retaining said wire loop member in said hook member, said refractor being swingable about said wire loop member while thus retained in said hook member.

6. In a luminaire, an upper inverted trough-shaped elongated housing, a lower trough-shaped elongated refractor forming a closure for said housing, molding strip means embracing and extending along the opposite upper edges of said refractor, said molding strip means and said housing each having outer bearing surfaces and inner sealing surfaces mating with each other in closed assembly, gasket means between said mating inner sealing surfaces, a plurality of combined latch and hinge means spaced from each other on each side of said assembled housing and refractor, each combined latch and hinge means holding said refractor in closed, fluid-tight engagement with said housing, and comprising a base member secured to said housing adjacent the bearing surfaces thereof and having spaced outwardly projecting flange portions, a lever member pivoted at one end to said flange portions, a wire loop member swingably secured to said lever member, and a hook member fixed to said molding strip means of said refractor, said wire loop being engageable with said hook member, and said lever member being movable about its pivot axis toward said housing for re taining said wire loop member in said hook member, said refractor being swingable about said wire loop member while thus retained in said hook member and when the combined latch and hinge means on the opposite side are disengaged.

7. In a luminaire, an elongated housing, an elongated refractor forming a closure for said housing, molding strip means secured to the edge of said refractor adjacent said housing, said housing and said molding strip means each being formed with supporting rail means extending along their length, and combined latch and hinge means mounted on said rail means of said housing and said molding strip means for holding said housing and said refractor in closed assembly said combined latch and hinge factor in closed assembly, said combined latch and hinge means when initially assembled on said housing and said molding strip means being slidable along said respective supporting rail means to predetermined position thereon.

8. A luminaire, comprising, in combination, an elongated inverted trough-shaped housing, an elongated trough-shaped refractor forming an enclosure for said housing and having upper longitudinal edges adjacent said housing in its closed position, molding strip means embracing and extending along said opposite upper longitudinal edges of said refractor, fixed latch means on one.

by side along the length thereof, each of said prisms on.

said refractor having prism faces at an angle to one another, said molding strip means being formed with angularly arranged bearing surfaces complementary to said angularly arranged prism faces and gripping thereby the prism faces of the uppermost prisms of said refractor.

9. A luminaire as defined in claim 8, wherein said molding strip means is formed with a recess at the junction of said angularly arranged bearing surfaces, said recess being filled with resilient sealing means for sealing the joint between said molding strip means and said refractor.

10. A luminaire comprising, in combination, an elongated inverted trough-shaped housing, and elongated trough-shaped refractor forming an enclosure for said housing and having upper longitudinal edges adjacent said housing in its closed position, molding strip means embracing and extending along said opposite upper longitudinal edges of said refractor, hook means secured to said refractor molding strip means, latch means pivotally secured to said housing and having a wire loop member swingably secured thereto, said wire loop member being engageable with said hook member, and said latch member being movable about its pivot axis toward said housing for retaining said wire loop member in said hook member, said refractor being swingable about said wire loop member while thus retained in said hook member.

References Cited UNITED STATES PATENTS 2,474,341 6/1949 Wince 240-93 2,731,288 1/1956 Langford 292258 2,775,001 12/1956 Baker 292-258 2,926,238 2/1960 Anderson et al 240-51.11 3,233,094 2/ 1966 Foulds 24025 FOREIGN PATENTS 80,146 2/1951 Czechoslovakia.

NORTON ANSI-1BR, Primary Examiner.

WYNDHAM M. FRYE, Assistant Examiner,

Claims

1. IN A LUMINAIRE, AN ELONGATED INVERTED TROUGH-SHAPED HOUSING HAVING OPPOSITE END WALLS CLOSING THE OPPOSITE ENDS THEREOF, EACH END WALL BEING FORMED ALONG ITS INNER SURFACE ADJACENT THE UPPER EDGE THEREOF WITH A CONTINUOUS RIDGE EXTENDING TRANSVERSELY OF SAID HOUSING IN A TORTUOUS PATH, THE UNDERSIDE OF SAID HOUSING HAVING DOWNWARDLY PROJECTING RIBS FORMED THEREIN, THE END PORTIONS OF WHICH ARE RECEIVED IN RECESSES FORMED IN SAID RIDGE, AND