Lighting fixture with thermal isolation

An outdoor lighting fixture is disclosed including a first housing containing the fixture ballast or power supply, a second housing enclosing a lamp. Each of the housings is sealed. A support stem joins the two housings and defines a thermal air gap between the two. The only conductive thermal path between the two housings is through the stem and the fasteners engaging the stem and the two housings. In one embodiment, a plurality of tubular spacers are located on elongated screw fasteners define the size of air gap. In another embodiment a single fastener includes washers defining the air gap size. In that embodiment, the fastener may be hollow and acts as a conduit for the electrical leads for the fixture. In another embodiment one closure for a housing includes fins for cooling the fixture.

BACKGROUND OF THE INVENTION

Throughout lighting industry and particularly, outdoor lighting such as walkway, flood and spot light applications, it is the desire of manufacturers and of the purchasers and the public that the lighting be reliable with lowest operating cost while meeting safe lighting requirements, require little or no maintenance and have long life. Weather, vandalism, and other factors can adversely affect the life of such fixtures and particularly their lamps and internal power supplies, such as ballasts or transformers.

The heat generated in the fixture itself in both the power supply which may be a transformer operating from typical 115-volt lines to serve low voltage lamps and the lamps themselves generate substantial heat. Heat generated by the fixture itself is a major factor in determining the operating life of the power supply or transformer and the lamp. A notable exception is solar powered lighting, however such systems rarely provide enough light for most applications where safety and reliability are controlling criteria.

The most common solution to the minimization of thermal damage to the key components, the power supply and the lamps in outdoor walkway and other architectural lighting is to provide large thermal conductive bodies such as aluminum housings which act as heat sinks and which sometimes have integral fins to aid in radiating the heat into the surrounding air. Fins, though effective, often detract from the ornamental appearance of the fixture.

An ideal shape for such outdoor walkway and other architectural applications is a cylindrical body, preferably with the power supply toward one end and the lamp assembly at the opposite end. That has given rise to fixtures with a fin section between the two heat sources with the expectation that it will serve to dissipate heat from both sections of the fixture while accepting the appearance of the fins. Examples of various finned fixtures are well known in the art.

BRIEF DESCRIPTION OF THE INVENTION

Faced with the present state of the art, one object of this invention is to provide walkway or other architectural lighting fixture with improved thermal energy removal.

Another object of this invention is to provide a lighting fixture with enhanced power supply and lamp life.

Still another object of this invention is to provide a lighting fixture in which the features responsible for enhanced thermal energy removal are virtually hidden from view.

Another object of the invention is to provide an attractive lighting fixture, which has enhanced protection from vandalism damage.

These objectives are achieved by a lighting fixture which includes a power supply housing, lamp and lamp housing or housings, a stem for mounting the fixture of metal having good thermal radiation properties assembled into an elongated structure. Internal, substantially concealed fastener or fasteners attach the housings to form one structure with a minimally visible thermal isolation air gap.

Some of the fasteners define one or more air gaps, which are located between the heat generating elements of the fixture, particularly the lamp and the power supply located in their respective housings.

The support stem for the fixture has substantial mass to radiate heat and to provide a rugged structural mount while conducting heat to whatever support to which it is attached.

Only one or two small fasteners such as setscrews, concealed at the bottom of the fixture provide access to the interior of the fixture in the event that access to the fixture is required.

In one embodiment, a single fastener joins the power supply housing to the stem and to the lamp and socket housing and constitutes the only thermal conduction path between the housings.

In other embodiments a plurality of internal fasteners joining the housings and the stem secure the entire assembly together while defining one or more air gaps and constitute the only thermal conduction path between the power supply housing, the stem and the lamp housing.

Another feature of the invention is a relatively massive swivel stem pivotally secured to the stem to provide a further thermal conduction path while conducting power leads to the stem and to the fixture providing angular adjustment of the orientation of the fixture.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of this invention may be seen inFIGS. 1 through 6with the external features appearing inFIGS. 1,2and6and the internal components inFIGS. 3 and 4and of a lighting fixture, generally designated10. The fixture10from the exterior comprises a power supply housing12, a supporting stem14and a lamp and socket housing16. The outer end of the housing16includes a shroud18as protection for the lens20of the fixture10which appears inFIGS. 1 and 6. Each of the foregoing defines an attractive, generally cylindrical body22with the stem14extending downward to constitute a support for the fixture10. A swivel stem24is located at the bottom of the stem14and is pivotable over an angle in the order of 60 or so degrees for adjusting the direction of the light beam emitted from the fixture10while supplying its operating power.

The support stem14and the swivel stem24include internal openings, unshown inFIG. 1for the passage of power leads26P from an external power line, unshown, to the interior of the fixture10where mating internal openings in the stem14and the power supply housing12provide external power to the power supply28ofFIGS. 3 and 4to the fixture.

From the standpoint of a casual observer, the fixture10appears to be a virtually continuous cylindrical structure, with a base provided by the stem14and the swivel stem24. Hardly noticeable is an air gap32which is in the order of less than ¼ inch in width extending around the body22adjacent to the stem where it matches the contour of the housings12and16. The internal (radial) surfaces defining the air gap32, preferably have the same color treatment as the body22as a whole, e.g. black finish, and become virtually invisible.

The air gap32, as described in more detail below, in combination with the body fasteners46F and spacer tubes ofFIG. 4are instrumental in providing enhanced thermal protection for the internal electrical components of the fixture, namely the lamp30, its socket32and the power supply transformer or ballast28ofFIGS. 3 and 4. Socket32is mentioned since they are commonly the first to suffer from heat damage in a fixture of any type.

Reference is now made toFIG. 3, which is a block diagram of the electronic elements of each of the embodiments of this invention. InFIG. 3, three incoming leads26, one black, one white, both power leads and one green which is the grounding lead for the fixture10constitute the input to the power supply28, identified inFIG. 3as the ballast, the socket34for the lamp36, shown in dashed lines within its reflector38. In accordance with this invention, the power supply28and the lamp36are virtually entirely thermally isolated from each other.

For a greater understanding of the invention, reference is now made toFIG. 4, which is an exploded view of the lighting fixture ofFIG. 1showing not only the housings12and16, the stem14and the swivel stem24but also showing the sealed internal power supply28which may be a transformer or ballast. A typical such power supply is a VS 39 watt 120 volt electronic ballast such as a Model MC39-1-F-1200 Ballast of the Hatch Transformer, Inc. when using a 39 watt PAR lamp or a 39 watt TC lamp. The ballast28has three input leads26, white, black and green (ground) and two output leads to the lamp socket34.

All of these leads extend out of the power supply (ballast) housing12through the housing12internal cover plate40and a lead tube42, to the socket housing44. The socket housing44is hollow and the lamp leads26L pass directly through housing44and are secured and electrically connected to respective terminals of socket34. Power leads26P extend part way through housing44and exit through its sidewall through port44P, through the mating port (unshown) of stem14and end port or slot of the swivel stem24to exit for connection to the local120vpower line when all is assembled and installed.

A plurality of fasteners46F such as machine screws, extend through matching openings in cover plate40, partially through the socket housing44and are secured in place by matching nuts46N. Tubes48slide over respective fasteners46F and are of sufficient length to space the housing12and its cover plate40by ⅛ to ¼ in. from the near edge of socket housing44and stem14, thereby creating air gap32ofFIGS. 1 and 2. Each of the openings in the cover plate40, and the housing44are sealed with silicone sealant or the like against any moisture. The cover plate40is threaded into matching threads in housing12and locked with a virtually hidden set screw SS on the underside of the fixture for security.

Key to this invention is the fact that the fasteners46F and tubes48are the only thermal conductive path between the ballast28, its housing12and the lamp36and its housing16. The entire body assembly22, the stem14and the swivel stem24constitute a thermal radiating body with an air gap32isolating the thermal conduction path between the two heat generating elements, the ballast28and the lamp36so neither can effectively transfer heat energy to the other.

FIRST ALTERNATE EMBODIMENT

Reference is now made toFIGS. 7 and 8for a basic version of this invention which not only serves to illustrate this invention but incorporates additional features serving to reduce the number of parts but provides equal or superior thermal isolation of the ballast and the lamp from each other and facilitates sealing the fixture and the process of wiring the fixture.

The fixture ofFIGS. 7 and 8, generally designated110comprises a power supply housing112with its threaded end closure113secured with a locking set screw SS, a stem114, with its swivel stem124, a lamp housing116and a shroud or lens protector118making up the major components viewable from the exterior. These structural components bear corresponding reference numerals similar to the embodiment ofFIGS. 1-6but in the one hundred series of numerals. Additional components visible inFIGS. 7 and 8from the exterior are two spacers, one of which,142appearing in bothFIGS. 7 and 8and spacer140appearing only inFIG. 8. These spacers140and142are actually metal washers. Spacer140which separates the ballast housing112from the stem114and spacer142which separates the stem114from the lamp housing116. These spacers140and142define three adjoining air gaps132,134and136, appearing inFIG. 8between the stem114and the two heat generating housings112and116. The three air gaps effectively separate the two heat generation components, namely the power supply28in housing112and the lamp136in housing116. The only thermal conductive path between the two housings112and116is through the spacers140and142and the fastener146that extends from housing112through the stem114to housing118. The fastener146passing through a close fitting bore in stem114is in direct thermal contact with the stem114for heat transfer by conduction out of the fixture110.

As shown inFIG. 8, the fastener146F is shown as hollow with a bore of sufficient size to allow the passage of the five wires, normally plastic insulated copper. The lamp leads126L pass entirely through the fastener146to the socket134while the power leads126P exit the fastener146through a hole in its sidewall shown in dashed lines to enter a mating bore in the stem114to exit the fixture110through a similar bore or slot in the swivel stem124to outside power.

The only thermal conductive path between the housing112and116is via the single fastener146and the spacers140and142which are in intimate contact with the stem114which is a readily available heat sink and thermal conductor to the support for the fixture.

This embodiment has minimum openings to the housings112and116that require sealing as compared with many exterior fixtures for enhanced protection from moisture intrusion.

When the fastener146is hollow as shown in the cutaway section ofFIG. 8and includes a sidewall smooth edged hole H, the power leads126P exit the fixture through that hole H and matching holes in the stem114and a matching slot in the swivel stem124to the external power source. Wiring paths are indicated inFIG. 5partially in solid lines and when hidden by dashed lines.

In accordance with this invention feature, all wiring within the fixture110passes through a single sealed passage in the stem114in the thermal dissipation path of the fixture and which may serve to provide cooling of the leads126P and126L, as well.

SECOND ALTERNATE EMBODIMENT

For high intensity lighting applications, for example, 150 watt, maximum which may utilize T6 CDM Type MH lamps. Fixtures incorporating the thermal dissipation features of the foregoing embodiments are modified in accordance with the second alternate embodiment which is shown inFIGS. 9 through 12.

The same components used in the embodiment ofFIGS. 1-5are used herein and bear the same reference numerals. The descriptions above for those figures will apply to this second alternate embodiment.

The fixture, generally designated210includes the power supply housing212, the stem214, the lamp housing216and the swivel stem224. The diameter of the fixture210may be larger than the previous embodiments, e.g., approximately 5 in. in diameter as compared with 2½ inch diameter for lower wattage fixtures.

The notable difference in this embodiment is the presence of a finned section260including a number of integral cooling fins262and a threaded end closure section264ofFIG. 11which seals the inner end of the lamp housing216. The opposite or outer end of the lamp housing216is closed by a threaded lens mounting ring268. A central core section270of the finned section260may be seen between the fins262along its central diameter. The central core270includes a through-hole272, appearing inFIG. 12allowing for the passage of leads26L and126L of the earlier figures to reach the lamp socket34as in the earlier embodiments.

The finned section260provides a heat radiating section in the fixture, aesthetically integrated into the fixture210as a whole and provides the further functions of sealing the fixture, conduction of electrical leads26P and26L and mounting the lamp housing216to the stem214.

General

Lamp fixtures in accordance with this invention, in general, are manufactured from machined or cast aluminum and have a durable exterior coating, O rings and silicone sealant in accordance with sound manufacturing standards as defined, particularly by the Underwriters Laboratories, Inc. They employ aluminum reflectors for the lamps and flat tempered or borosilicate glass lens secured in place by silicone sealant.

The preferred lamps, depending upon the wattage requirements are as follows:

Suppliers of the foregoing lamps and ballasts are well known in the lighting field.

Pre-production lighting fixtures incorporating the principles of this invention have met all of the standards of the Underwriters Laboratories, Inc. Standard 1598 for luminere including the temperature rise requirements and Canadian CSA standards C22.2 No. 250.0 and the Canadian specific standards.

The versatility of fixtures incorporating this invention to accommodate the broad range of power ratings is believed to be owed, at least in part, to the thermal dissipation capabilities afforded by this invention.

The foregoing embodiments and the descriptions are representative of the preferred embodiments of this invention and are not to be considered as limiting. Rather, the invention must be determined by reference to the following claims, as stated below and given the protection afforded by the Doctrine of Equivalents.