Lighting apparatus

A lighting apparatus is provided including an array of light emitting diodes (LEDs) disposed on a base. The base is configured to move heat away from the array of LEDs to other portions of the base and further to the atmosphere or an adjacent housing. In one embodiment, a native oxide on the base electrically insulates the base from the LEDs. In another embodiment, a cover is removably disposed over the array of LEDs, and removal of the cover prevents electrical energization of the LEDs.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to light emitting diode (LED) lighting devices and more particularly to LED lighting modules having heat transfer properties that improve the efficiency and performance of LEDs.

2. Description of the Related Art

Most lighting applications utilize incandescent or gas-filled bulbs, particularly lighting applications that require more than a low level of illumination. Such bulbs typically do not have long operating lifetimes and thus require frequent replacement. Gas-filled tubes, such as fluorescent or neon tubes, may have longer lifetimes, but operate using dangerously high voltages and are relatively expensive. Further, both bulbs and gas-filled tubes consume substantial amounts of power.

In contrast, light emitting diodes (LEDs) are relatively inexpensive, operate at low voltage, and have long operating lifetimes. Additionally, LEDs consume relatively little power and are relatively compact. These attributes make LEDs particularly desirable and well suited for many applications.

Although it is known that the brightness of the light emitted by an LED can be increased by increasing the electrical current supplied to the LED, increased current also increases the junction temperature of the LED. Increased junction temperature may reduce the efficiency and the lifetime of the LED. For example, it has been noted that for every 10° C. increase in temperature above a specified temperature, the operating lifetime of silicone and gallium arsenide drops by a factor of 2.5-3. LEDs are often constructed of semiconductor materials that share many similar properties with silicone and gallium arsenide.

Accordingly, there is a need for an apparatus to efficiently remove heat from LEDs in order to decrease the junction temperature during use and thereby increase the operating lifetime of the LEDs.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a lighting apparatus is provided comprising a base comprised of an electrically conductive material and a layer of oxide on the material. An array of LEDs is mounted on the base. The LEDs are electrically insulated from the conductive material by the oxide. In another embodiment, the base includes electrically conductive traces disposed on the oxide, which traces interconnect the LEDs in the array.

In accordance with a further embodiment, a lighting apparatus is provided comprising a base, an array of LEDs mounted to the base, and a cover configured to cover the array. Power is supplied to the LEDs via an electrical pathway. The cover is mechanically coupled to the base such that attachment of the cover completes the electrical pathway to permit power to flow to the LEDs, and removal of the cover opens the electrical pathway to prevent flow of power.

In accordance with a still further embodiment, the lighting apparatus additionally comprises a power supply having first and second power supply nodes. The base and cover are attachable to the power supply so that the first and second nodes electrically communicate with the cover to complete the electrical pathway.

In accordance with another embodiment, a lighting apparatus is provided comprising a base, an array of LEDs mounted on the base, and a cover comprising a sheet that covers the array of LEDs and receives light from the LEDs. The sheet is comprised of a phosphor which emits light in response to optical pumping by the LEDs.

In a further embodiment, the base comprises a cavity, the array of LEDs is arranged in the cavity, and the cover is configured to completely enclose the cavity when the cover is in place so that substantially no light emitted by the LEDs exits the cavity without first contacting the cover.

In still another embodiment, the sheet comprises more than one layer. In yet another embodiment, the cover comprises glass, and the phosphor is mixed with the glass. In further embodiments, the sheet consists of inorganic material, and the LEDs emit ultraviolet light.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain aspects of embodiments have been described herein above. Of course, it is to be understood that not necessarily all such aspects may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one aspect or group of aspects as taught herein without necessarily achieving other aspects as may be taught or suggested herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With initial reference toFIGS. 1-3, an embodiment of a lighting apparatus30is illustrated. The lighting apparatus30preferably comprises a power module32and a light emitting diode (LED) module34that are connected to one another. In summary, the LED module34comprises a heat conductive base40upon which a plurality of electrically conductive traces42are disposed. An array of LEDs44is mounted on the base40and electrically connected to the traces42. Transmissive material46is disposed in and around the LEDs44, and a cover50is placed thereover. The cover50preferably comprises a phosphor.

With continued reference toFIGS. 1-3, the power module34comprises an elongate body52having a first end54and a second end56. Each of the first and second ends54,56include positive and negative connectors58,60that are adapted to connect to flexible conductors such as electrical wire. Further, the first and second ends54,56each include a mounting flange62adapted to receive a fastener in order to secure the lighting apparatus30to a mount surface. In other embodiments, other mounting structures and methods can be employed. For example, two-sided tape can be disposed on a bottom surface64of the power module32in order to secure the apparatus to a mount surface.

The power module32preferably is configured to be powered by an external power supply and receives constant input voltage of about 12 or 24 volts DC. Preferably, the power module32converts the constant input voltage into a constant current for electrically driving the LEDs44of the LED module34. The current preferably is pulsed with a frequency in excess of about 300 Hz. A power module32exhibiting such electrical behavior can be obtained from Advance Transformer/Phillips.

With specific reference toFIG. 2, the illustrated power module32has a generally flat mount surface66configured to engage and support the LED module34. First and second mount holes68,70facilitate mounting of the LED module34to the power module32. Power is supplied from the power module32to the LED module34between an input node72and an output node74. In the illustrated embodiment, the input and output nodes72,74are disposed at or in the first and second mount holes68,70.

With reference also toFIGS. 4-8, the base40preferably has a bottom surface80, a top surface82, first and second sides84,86, and first and second ends90,92. Mount holes94,96are disposed adjacent the first and second ends90,92, respectively, and are configured to align with the mount holes68,70in the power module32. The top surface82preferably has a cavity100formed therein. An upper wall102extends from the top surface82to a step104. A lower wall106extends from the step104to a cavity surface110. The portion of the cavity100defined within the upper wall102and step104is referred to as an upper cavity112; the portion of the cavity100defined within the lower wall106between the step104and the cavity surface110is referred to as a lower cavity114.

With continued reference specifically toFIGS. 4-8, the base40comprises a first portion120and a second portion122. The majority of the volume of the base40comprises the first portion120, which preferably is constructed of a heat conductive material, such as a metal or metal alloy. In the illustrated embodiment, the first portion120comprises an aluminum silicon carbon (AlSiC) material. It is to be understood that, in other embodiments, the first portion can be made of other heat conductive materials, and even a combination of two or more different heat conductive materials.

The second portion122of the base40preferably comprises a relatively thin sheet of another heat conductive material. In some embodiments, the sheet is referred to as a heat conductive insert. A coefficient of thermal conductivity of the second portion122is greater than a coefficient of thermal conductivity of any part of the first portion120. In the illustrated embodiment, the second portion122is centered just below the cavity100and is enclosed within the base40. Heat from within the lower cavity114is drawn into the first portion120and flows readily to the second portion122. Due to its high heat conductance properties, the second portion122distributes heat received from the lower cavity away from the lower cavity and to other locations within the first portion120, specifically to the first and second sides84,86which, in the illustrated embodiment, are part of the first portion120. From the sides84,86, the heat is radiated away from the base40to the atmosphere or an adjacent heat sink.

The second portion122preferably comprises a relatively thin generally planar sheet comprising a material having not only high thermal conductivity, but also having directional thermal conductivity properties. For example, preferably the flat sheet of the second portion122conducts heat in a plane generally parallel to a center plane of the flat sheet of material. In the illustrated embodiment, the second portion122comprises strands of material that preferentially conduct heat along the length of the strand. The strands preferably are oriented to direct heat toward the first and second sides84,86of the second portion. Further, in the illustrated embodiment the second portion122comprises carbon strands and, more specifically, highly-oriented pyrolytic graphite. Most preferably, the second portion has a very high thermal conductivity, such as greater than about 1,000 W/(m*K) or, in another embodiment, at least about 1,350-1,450 W/(m*K).

A base member having properties as discussed above in connection with the illustrated embodiment can be obtained from Ceramics Process Systems Corporation of Chartly, Mass.

In other embodiments, the second portion comprises a relatively thin sheet that is made of a material having a high thermal conductivity but which does not necessarily preferentially conduct heat in a plane generally parallel to a center plane of the second portion. In further embodiments, the second portion may vary in size, shape and layout. For example, in one embodiment, the second portion has a pyramid-shaped cross-section and is disposed beneath the cavity surface110.

In the illustrated embodiment, the second portion122is disposed generally in the center of the base40, and is substantially enclosed within the first portion120. It is to be understood that, in other embodiments, the second portion can extend further from the center into the first and second sides, and can even extend out of at least one of the sides of the base. In yet further embodiments, the first portion may include fins to radiate heat to the atmosphere surrounding the first portion.

As discussed above, the base40preferably is made of a heat conductive material. In the illustrated embodiment, the base comprises AlSiC, which is also electrically conductive. In accordance with a preferred embodiment, the electrically conductive base comprises a layer of oxide disposed thereon. Preferably, the oxide is a native oxide of the electrically conductive material of which the base is made. Further, the oxide layer preferably has a thickness of about 2 mils or less. In one embodiment, a native oxide layer is grown on the conductive base40via an anodization process. More particularly, the base preferably is anodized in an electrochemical bath in order to grow the native oxide thereon. It is to be understood that, in other embodiments, other methods and apparatus can be used to deposit a non-conductive layer on the base. For example, powder coating or plating with any non-electrically-conductive electroless metal can be acceptable.

In the illustrated embodiment, the native oxide grown through anodization functions as a dielectric to electrically insulate the base40. With next reference toFIGS. 2,9,10and10a, electrically conductive circuit traces42preferably are disposed on the cavity surface110of the base40, and are attached to the oxide layer. As such, the electrical traces42are electrically insulated from the base40by the oxide layer. The electrically conductive traces42are arranged to provide an electrical pathway to power a plurality of LEDs44attached to the traces. Contact pads126of the traces42are configured to accept LEDs mounted thereon. In the illustrated embodiment, the contact pads126are thicker than other portions of the traces42.

In the illustrated embodiment, the electrical circuit traces42are configured to mount ten LEDs44in an electrically parallel fashion. It is to be understood that, in other embodiments, any desired number of LEDs can be used, and different electrical arrangements can be employed. For example, the LEDs can be arranged electrically in series. Also, more than one set of serially-connected LEDs can be arranged so that the sets are electrically in parallel relative to one another within the cavity100. Further, the LEDs can be disposed in different mechanical arrangements. For example, in the illustrated embodiment, the ten LEDs44are equally spaced and arranged in a serial array. It is to be understood that other spacings and arrangements can be accomplished as desired.

In the illustrated embodiment, the circuit traces42comprise an electrically conductive material such as aluminum or another metal laid upon the oxide layer of the base40. The base40is electrically insulated from the power traces42by the non-conductive oxide layer. The power traces42are laid on the oxide layer by any suitable method, including methods currently employed by vendors such as Kyocera and IJ Research.

With next reference to FIGS.3and9-12, the power traces42have terminus portions128disposed adjacent the mount holes94,96at either end of the base40. A conductive contact member130preferably is electrically connected at each terminus128and extends upwardly from the power traces42. Preferably the contact member130extends upwardly up to or beyond the level of the step104between the upper and lower walls102,106in the cavity100. Preferably, the contact member130is bonded, co-formed, or otherwise attached to the respective terminus portion128. For example, in one embodiment, the contact member130is soldered in place on the terminus portion128. In the illustrated embodiment, the contact member130comprises a cylindrical pin. It is to be understood that, in other embodiments, other shapes and sizes of contact members can be employed.

With reference next toFIGS. 2,3and12, the lower cavity114preferably is filled with a transmissive material46. In the illustrated embodiment the transmissive material46comprises a mixture of silicone and glass. In One embodiment, the transmissive material46is chosen from materials known as sol-gels. In another embodiment, the transmissive material46comprises a mixture of silicone and glass available under the trademark Sogel™, which can be obtained from WaveGuide.

The cover50is configured to be disposed over the cavity100of the base40so as to cover the array of LEDs44and receive light from the LEDs. In the illustrated embodiment and with reference specifically toFIGS. 2,3and12-14, the cover50preferably comprises a multi-layer sheet132. The sheet132comprises first and second layers134,136of glass that sandwich a layer of phosphor138. The glass and phosphor layers134,136,138preferably are connected by a layer of adhesive139.

In the illustrated embodiment, the phosphor138is sandwiched between two layers of glass134,136. In another embodiment the phosphor is mixed, embedded and/or suspended in the glass so that the sheet comprises only a single layer of phosphor-including glass. In a preferred embodiment, the sheet comprises inorganic material that will not degrade when exposed to ultraviolet light. Further, in such an embodiment, the LEDs are configured to emit ultraviolet light. In further embodiments, the cover50sheet can be colored or include one or more colored layers, and may or may not include a phosphor.

Continuing with reference toFIGS. 2,3and12-16, the sheet132of the cover50preferably is held on either end by a cover frame140. With particular reference toFIGS. 15A-C, each cover frame140preferably includes a body142having a mount hole144formed therethrough, which mount hole144is configured to align with the mount holes144of the base40and power module32. A gripping portion146of the frame body142comprises opposing jaws148that are configured to hold the sheet132.

When the cover50and base40are assembled, as shown inFIGS. 3 and 12, the cover50is configured to fit at least partially within the upper wall102in the upper portion112of the base cavity100. Preferably, the cover50fits generally snugly in the upper portion112so that substantially no light emitted by the LEDs44exits the cavity100without first contacting the cover50. In another embodiment, the cover50generally engages the step104so as to substantially enclose the lower portion114of the cavity100.

In the illustrated embodiment, the transmissive material46is deposited in the cavity100so as to surround the LEDs44. As the cover50is placed in the cavity100, excess transmissive material46will squeeze past the cover50and can be removed from the device. As such, the sheet132preferably abuts the transmissive material46and/or the LEDs44so that there is very little or substantially no air between the LEDs44and the cover sheet132.

In the illustrated embodiment the transmissive material46, LEDs44, and sheet132comprise a graduated refractive index. More specifically, in the illustrated embodiment the LEDs44each preferably have a refractive index of between about 2.1 to 2.8. The transmissive material46preferably has a refractive index between about 1.5 to 1.8. A first layer of glass134in the sheet preferably has a refractive index between about 1.45 to 1.5. A second layer of glass136in the sheet preferably has a refractive index of about 1.40 to 1.45. As such, the several different layers of materials collectively comprise a graduated refractive index, and the refractive indices of the layers are relatively closely matched so as to maximize light output from the apparatus30. In embodiments wherein the cover50comprises a phosphor138, light from the LEDs44is absorbed by the phosphor, which emits light in response to such optical pumping by the LEDs.

With reference particularly to FIGS.12and16A-C, a contact sleeve150preferably is disposed in each cover frame hole144. The contact sleeve150preferably is made of a conductive material such as a metal. In the illustrated embodiment, the contact sleeve150comprises an elongate body portion152that is configured to fit through the cover frame hole144, and a flange portion154that extends radially outwardly from the body portion152. With particular reference toFIGS. 3 and 12, the contact sleeve150is fit within the cover frame140and the cover50is placed on the base40so that the flange portion154of the contact sleeve150contacts and engages the corresponding contact member130. A threaded mount bolt160extends through each contact sleeve150, through the base40, and into the corresponding mount holes68or70of the power module32. Threads within the power module mount holes68,70engage the respective mount bolts160so that the assembly is securely held together. As discussed above, the first and second mount holes68,70of the power module32comprise first and second electrical nodes72,74. As such, when engaged in the threaded mount holes68,70, the mount bolts160are electrically energized.

As best shown inFIGS. 3 and 12, and as discussed above, when the cover50is installed, the flange portion154of the contact sleeve150engages the contact member130, which extends upwardly from the conductive traces42. Thus, an electrical circuit is completed creating an electrical pathway from the first node72of the power supply module32through the first bolt160and contact sleeve150into the contact member130and further through the power traces42and LEDs44. From the power traces42the electrical pathway proceeds to the second contact member130, second contact sleeve150, second bolt160and further to the second node74. When the power module32is energized, current flows along this pathway to drive the LEDs44. When the cover50is removed, however, there is no electrical pathway between the power supply module nodes72,74and the contact members130. In this manner, the LEDs44of the LED module34cannot be powered when the cover50is not in place. As such, worker safety when working with such lighting apparatus30is enhanced, especially when ultraviolet light-emitting LEDs are in use, because the LEDs will not be powered, and thus will not be lit, without the protective cover in place.

Although the illustrated embodiment shows the cover50being connected to the module32,34by first and second threaded bolts160, it should be appreciated that the mechanical connection used to complete the electrical pathway may be any mechanical or other connection known in the art. For example, other connections may include clamps, pins, screws, detents, solder, conductive adhesives, etc. Similarly, it is to be understood that other configurations of the power supply nodes may appropriately be used. Additionally, the contact sleeves and power node connections may be threaded so as to enhance the mechanical and electrical connection between the mount bolts160, sleeve150and power module nodes72,74.

In another embodiment, at least portions of the cover frames140are electrically conductive and, rather than employ a contact sleeve, each cover frame140comprises an engagement portion shaped and configured to engage the contact member130when the cover50is secured in place on the base40. In this embodiment, the power supply nodes preferably are configured to electrically engage the respective cover frame when the cover is in place so that an electrical pathway is established between the nodes and the contact members through the cover frames.

In still another embodiment, one of the circuit terminus portions is electrically connected to a respective power supply node through a trace configured to electrically engage the bolt without electrically contacting the cover. The other terminus portion preferably electrically engages the cover. As such, the electrical pathway between power module nodes flows through only one end of the cover.

In a further embodiment, multiple covers may be provided for a single lighting apparatus30, each cover having different color and/or phosphor properties. As such, lighting properties of each lighting apparatus30can be modified by simply changing the cover50.

With reference next toFIG. 17, each lighting apparatus30is configured to be connected to other such lighting apparatus30by flexible conductors164. A common power supply166is configured to supply power to the respective apparatus30. It is to be understood that several such lighting apparatus30can be joined end-to-end in a daisy-chain arrangement and used for various applications. In the illustrated embodiment, the power supply modules32are configured so that the lighting apparatus30are connected electrically in parallel. In another embodiment, the modules32may be configured so that such a daisy-chain arrangement is electrically in series.

With next reference toFIGS. 18 and 19, a housing170preferably comprises a channel172that is configured to slidably accept a plurality of lighting apparatus30therewithin. For aesthetic purposes, and to ensure proper spacing between connected lighting apparatus30, a spacer174preferably is fit between adjacent lighting apparatus30within the channel172. Preferably the housing170comprises a thermally conductive material such as aluminum or another metal. With particular reference toFIG. 19, upper and side walls176,178of the housing channel172are configured to engage top and side surfaces82,84,86of the base40so that heat that is drawn from the LEDs44and directed to the sides84,86of the base40is further conducted from the sides84,86to the housing170. Additionally, in accordance with one embodiment, the power supply mount surface66is heat conductive to further facilitate conduction of heat away from the base40.

As shown inFIG. 19, the side walls178of the housing172preferably have a plurality of fins180so as to aid in convection and thus speed dissipation of heat. As such, heat is drawn quickly from the LEDs44through the base40and into the housing170, from which it is radiated to the environment. In the illustrated embodiment, the second portion122of the base40facilitates such a heat pathway by quickly communicating heat generated by the LEDs44within the lower cavity114toward the sides84,86of the base40and to the fins180, which are adjacent the sides84,86.

With continued reference toFIGS. 18 and 19, in the illustrated embodiment the convective fins180in the housing170are enclosed within a cover182so as not to be seen from outside the housing170. It is to be understood that, in other embodiments, the convective fins180may be readily viewed from outside the housing170.