Patent Application
20130194796
1. Field of the Invention
This invention relates to solid state lamps and bulbs and in particular to light emitting diode (LED) based lamps and bulbs capable of providing omnidirectional emission patterns similar to those of filament based light sources.
2. Description of the Related Art
Light emitting diodes (LED or LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active layer where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED.
In order to use an LED chip in a circuit or other like arrangement, it is known to enclose an LED chip in a package to provide environmental and/or mechanical protection, color selection, light focusing and the like. An LED package also includes electrical leads, contacts or traces for electrically connecting the LED package to an external circuit. In a typical LED package 10 illustrated in
A conventional LED package 20 illustrated in
LED chips, such as those found in the LED package 20 of
Lamps have been developed utilizing solid state light sources, such as LEDs, with a conversion material that is separated from or remote to the LEDs. Such arrangements are disclosed in U.S. Pat. No. 6,350,041 to Tarsa et al., entitled “High Output Radial Dispersing Lamp Using a Solid State Light Source.” The lamps described in this patent can comprise a solid state light source that transmits light through a separator to a disperser having a phosphor. The disperser can disperse the light in a desired pattern and/or changes its color by converting at least some of the light through a phosphor. In some embodiments, the separator spaces the light source a sufficient distance from the disperser such that heat from the light source will not transfer to the disperser when the light source is carrying elevated currents necessary for room illumination.
Different LED based bulbs have been developed that utilize large numbers of low brightness LEDs (e.g. 5 mm LEDs) mounted to a three-dimensional surface to achieve wide-angle illumination. These designs, however, do not provide optimized omnidirectional emission that falls within standard uniformity requirements. These bulbs also contain a large number of interconnected LEDs making them prohibitively complex, expensive and unreliable. This makes these LED bulbs generally impractical for most illumination purposes.
Other LED bulbs have also been developed that use a mesa-type design for the light source with one LED on the top surface and seven more on the sidewalls of the mesa. (see GeoBulb®-II provided by C. Crane). This arrangement, however, does not provide omnidirectional emission patterns, but instead provides a pattern that is substantially forward biased. The mesa for this bulb also comprises a hollow shell, which can limit its ability to thermally dissipate heat from the emitters. This can limit the drive current that can be applied to the LEDs. This design is also relatively complex, using several LEDs, and not compatible with large volume manufacturing of low-cost LED bulbs.
The present invention provides various embodiments of solid state lamps and bulbs that are efficient, reliable and cost effective and can be arranged to provide omnidirectional emission patterns. The different embodiments comprise elements to elevate the solid state light source(s) above the lamp base, with the elevating element also being thermally conductive to conduct heat from the light source to the lamp base. The elevating element can comprise many different materials or devices arranged in different ways, with some lamps comprising heat pipe elevating elements.
One embodiment of solid state lamp according to the present invention comprises a solid state light source and a lamp base at least partially comprising a heat conductive material. An elongated elevating element is mounted to the lamp with the light source mounted to the elevating element such that the LEDs are above the lamp base, with the elevating element being at least partially heat conductive. A diffuser is also included to diffuse light emitting from lamp into the desired emission pattern.
One embodiment of a light emitting diode based bulb according to the present invention comprises a heat pipe and a plurality of light emitting diodes, each of which is mounted at or near a first end of, and in thermal contact with, the heat pipe. The heat pipe comprises a thermally conductive path to conduct heat away from the light emitting diodes. A lamp base is included that at least partially comprises a heat conductive material. The second end of the heat pipe is mounted to, and in thermal contact with, the heat pipe, with the lamp base comprising a thermally conductive path to conduct heat away from the heat pipe.
Another embodiment of a solid state lamp according to the present invention comprises a heat pipe having a plurality of solid state light sources in thermal contact with the heat pipe. A heat sink structure is included with the heat pipe thermally coupled to the heat sink structure. Heat from the solid state light sources conducts to the heat sink structure through the heat pipe. A diffuser is arranged with at least some light from the light sources passing through the diffuser.
These and other further features and advantages of the invention would be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which:
The present invention is directed to different embodiments of solid state lamp structures that in some embodiments provide elevating elements to mount LED chips or packages (“LEDs”) above the lamp base. The elevating elements can comprise many different thermally conductive materials, as well as multiple material devices arranged to conduct heat. In some embodiments, the elements can comprise one or more heat pipes, with the LEDs mounted to the one end of and in thermal contact with the heat pipe. The other end of the heat pipe can be mounted to the lamp base with the heat pipe in an orientation to elevate the LEDs above the base. The heat pipes also conduct heat from the LEDs to the lamp base where the heat can efficiently radiate into the ambient. This arrangement allows for the LEDs to operate at a lower temperature, while allowing the LEDs to remain remote to the lamp base, which can be one of the lamp's primary heat dissipation features. This in turn allows for the LEDs to be driven with a higher drive signal to produce a higher luminous flux. Operating at lower temperatures can provide the additional advantage of improving the LED emission and increase the LED lifespan.
Heat pipes are generally known in the art and are only briefly discussed herein. Heat pipes can comprise a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two interfaces. At the hot interface (i.e. interface with LEDs) within a heat pipe, a liquid in contact with a thermally conductive solid surface turns into a vapor by absorbing heat from that surface. The vapor condenses back into a liquid at the cold interface, releasing the latent heat. The liquid then returns to the hot interface through either capillary action or gravity action where it evaporates once more and repeats the cycle. In addition, the internal pressure of the heat pipe can be set or adjusted to facilitate the phase change depending on the demands of the working conditions of the thermally managed system.
A typical heat pipe includes a sealed pipe or tube made of a material with high thermal conductivity such as copper or aluminum at least at both the hot and cold ends. A vacuum pump can be used to remove air from the empty heat pipe, and the pipe can then be filled with a volume of working fluid (or coolant) chosen to match the operating temperature. Examples of such fluids include water, ethanol, acetone, sodium, or mercury. Due to the partial vacuum that can be near or below the vapor pressure of the fluid, some of the fluid can be in the liquid phase and some will be in the gas phase.
This arrangement of elevating the LEDs on a heat pipe can provide a number of additional advantages beyond those mentioned above. Remote placement of the LEDs on a heat pipe can allow for a concentrated LED light source that more closely resembles a point source. The LEDs can be mounted close to one another on the heat pipe, with little dead space between adjacent LEDs. This can result in a light source where the individual LEDs are less visible and can provide overall lamp emission with enhanced color mixing. By elevating the LED light source, greater angles of light distribution are also available, particularly emission in the down direction (compared to planar source on base). This allows the lamps to produce more omnidirectional emission pattern, with some embodiments comprising an emission pattern with intensity variation of approximately +20 percent or less. Still other embodiments can comprise an emission pattern having an omnidirectional emission pattern with intensity variation of approximately +15 percent or less.
In some embodiments the emission patterns can meet the requirements of the ENERGY STAR® Program Requirements for Integral LED Lamps, amended Mar. 22, 2010, herein incorporated by reference. The elevated LEDs along with the relative geometries of the lamp elements can allow light to disperse within 20% of mean value from 0 to 135 degrees with greater than 5% of total luminous flux in the 135 to 180 degree zone (measurement at 0, 45 and 90 azimuth angles). The relative geometries can include the lamp mounting width, height, head dissipation devices width and unique downward chamfered angle. Combined with a diffuser dome, the geometries can allow light to disperse within these stringent ENERGY STAR® requirements.
The present invention can reduce the surface areas needed to dissipate LED and power electronics thermal energy and still allow the lamps to comply with ANSI A19 lamp profiles 30 as shown in
Different embodiments can be used with diffuser domes and by concentrating the light source on the heat pipe within the diffuser dome, there can be an increased distance between the light source and the diffuser. This allows for greater color mixing as the light emits from the LEDs and as the light passes through the diffuser dome. LED lamps according to the present invention can also have power supply units that generate heat and are typically located in the lamp base. Elevating of the LEDs above the base on heat pipe separates the heat generating LEDs from the heat generating power supply units. This reduces thermal “cross-talk” between the two and allows for both to operate at lower temperatures. The remote arrangement can also allow for directional positioning of the LEDs on the heat pipe to provide the desired lamp emission pattern. This directional emission can be provided from LEDs mounted to different up and down angled surfaces to provide the desired emission.
In the embodiments utilizing a diffuser, the diffuser not only serves to mask the internal components of the lamp from the view by the lamp user, but can also disperse or redistribute the light from the remote phosphor and/or the lamp's light source into a desired emission pattern. In some embodiments the diffuser can be arranged to assist in disperse light from the LEDs on the heat pipe into a desired omnidirectional emission pattern.
The properties of the diffuser, such as geometry, scattering properties of the scattering layer, surface roughness or smoothness, and spatial distribution of the scattering layer properties may be used to control various lamp properties such as color uniformity and light intensity distribution as a function of viewing angle. By masking the internal lamp features the diffuser can provide a desired overall lamp appearance when the lamp or bulb is not illuminated.
The lamp base can also comprise a heat sink structure with the heat pipe arranged in thermal contact with the heat sink structure. In some embodiments, the heat sink structure can comprise heat dissipating fins to radiate heat from the heat sink structure to the ambient. The lamp base can also comprise a means for connecting the lamp to a power source, such as a connector to connect to an Edison type socket, etc.
The features of the different lamp embodiments described herein can provide a solid state lamp that produces an emission pattern that more closely matches a traditional incandescent light bulb in form and function. These features also allow for emission with the intensity, temperature and color rendering index (CRI) that also resembles those of a traditional incandescent light bulb. This allows some lamp embodiments having the advantages of a solid state light source, such as LEDs, that are particularly applicable to uses as replacement bulbs for incandescent bulbs.
Lamps have been developed that utilize a larger shaped remote phosphor that can convert some the LED light. These larger phosphors, however, can result in higher material costs for the larger remote phosphor, and an envelope for the lamp. The present invention is arranged such that white emitting LEDs providing the desired CRI and color temperature can be mounted to the heat sink to provide the desired lamp emission. This allows for some lamps according to the present invention to operate without the complexity and expense of a remote phosphor, such as a phosphor globe.
It is understood, however, that other embodiments of LED lamps according to the present invention can be used in combination with a shaped remote phosphor, with the remote phosphor also being mounted to the heat sink. The remote phosphor can take many different shapes, such as a general globe-shape with the heat pipe at least partially arranged within the globe shaped phosphor. This can provide an arrangement with the desired color uniformity by the heat pipe and its emitters providing an approximate point light source within the remote phosphor. Many different remote phosphors are described in U.S. patent application Ser. No. 13/018,245, titled “LED Lamp with Remote Phosphor and Diffuser Configuration”, filed on Jan. 31, 2011, which is incorporated herein by reference.
The present invention is described herein with reference to certain embodiments, but it is understood that the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In particular, the present invention is described below in regards to certain lamps or lighting components having LEDs, LED chips or LED components (“LEDs”) in different configurations, but it is understood that the present invention can be used for many other lamps having many different configurations. The components can have different shapes and sizes beyond those shown and different numbers of LEDs or LED chips can be included. Many different commercially available LEDs can be used such as those commercially available LEDs from Cree, Inc. These can include, but are not limited to Cree's XLamp® XP-E LEDs or XLamp® XP-G LEDs.
It is also understood that when an element such as a layer, region or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. Furthermore, relative terms such as “inner”, “outer”, “upper”, “above”, “lower”, “beneath”, and “below”, and similar terms, may be used herein to describe a relationship of one layer or another region. It is understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.
Embodiments of the invention are described herein with reference to cross-sectional view illustrations that are schematic illustrations of embodiments of the invention. As such, the actual thickness of the layers can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances are expected. Embodiments of the invention should not be construed as limited to the particular shapes of the regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. A region illustrated or described as square or rectangular will typically have rounded or curved features due to normal manufacturing tolerances. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the invention.
The heat sink structure 50 can also comprise a smooth outer surface and in other embodiments can comprise other heat dissipation features such as heat fins that increase the surface area of the heat sink to facilitate more efficient dissipation into the ambient. In some embodiments, the heat fins can be made of same material or a material with higher thermal conductivity than the remainder of the heat sink structure. The heat fins have a generally vertical orientation, but it is understood that in other embodiments the fins can have a horizontal or angled orientation, or combinations of different orientations. In still other embodiments, the heat sink can comprise active cooling elements, such as fans, to lower the convective thermal resistance within the lamp.
The base 42 can also comprise different areas of solid heat conducting material and different open areas to house lamp features such as a power supply unit as described below. In some embodiments the portion above the connector 52 can comprise a substantially solid heat conducting material, with some embodiments having heat fins that radiate out from the solid material. The heat pipe 44 can be mounted to the lamp base using many different mounting methods and materials. As best shown in
The heat pipe 44 can be held in place using many different material and mechanisms, and in the embodiment shown be bonded in countersunk hole 54 using different materials, such as thermally conductive materials that allow heat to spread from the heat pipe 44 to the lamp base 42. One suitable binding material comprises a thermal epoxy, but it is understood that many different thermally conductive materials can be used such as thermally conductive grease. Conventional thermally conductive grease can contain ceramic materials such as beryllium oxide and aluminum nitride or metal particles such as colloidal silver. In one embodiment a thermal grease layer is used having a thickness of approximately 100 μm and thermal conductivity of k=0.2 W/m-k. This arrangement provides an efficient thermally conductive path for conducting heat from the heat pipe 44 to the heat sink structure 50.
It is also understood that the arrangement shown in
The connector 52 is included on the base 42 to allow for the lamp 40 to connect to a source of electricity such as to different electrical receptacles. In some embodiments, such as the one shown in
As best shown in
As mentioned above, the LEDs 46 can be mounted to the heat pipe 44 at different locations, with a suitable location being at or near the end of the heat pipe 44 opposite the lamp base 42. The LEDs 46 can be mounted in many different ways, but should be mounted such that there is an efficient thermal path from the LEDs 46 to the heat pipe 44. In some embodiments, the LEDs 46 can be mounted directly to the heat pipe 44 by a thermally conductive material such as a solder. In the embodiment shown, a conductive block 56 of conductive material is provided at or near the top of the heat pipe 44, with the block 56 being in thermal contact with the heat pipe 44. The conductive block 56 can be made of many different thermally conductive materials such as copper, conductive plastic, or aluminum, and can be bonded with a conductive material to provide the efficient conductive path between the block 56 and the heat pipe 44. The block 56 provides planar surfaces that can be compatible with mounting LEDs and LED packages.
The lamps according to the present invention can utilize different numbers of LEDs or LED packages, with the embodiment shown having two LEDs 46 mounted to opposing sides of the conductive block 56. It is understood that other embodiments can have more LEDs, and in some embodiments it may be advantageous to have an LED mounted to the top of the block 56 or on more than two surfaces of the conductive block 56 to provide the desired emission pattern. The conductive block 56 has a cube shape, but it is understood that the block can have different shapes that have more or less side surfaces, or can have surfaces angled in one direction, such as up in the case of a pyramid, or having surfaces angled in both up and down directions, such as in the case of a diamond. It is understood that the block can take many different shapes having different numbers of up or down angled surfaces, with different embodiments having four or more planar surfaces, including the bottom facing surface.
In the embodiment shown the block 56 is arranged to hold two LEDs 46, with each on opposing sides of the block 56. The conductive block 56 is thinner on the uncovered side surfaces to bring the back-to-back LEDs 46 in closer proximity to one another so that the overall light source more closely resembles a point light source. The LEDs are arranged at a height within the diffuser dome to provide the desired lamp emission pattern. By raising the LEDs 46 above the lamp base on the heat pipe 44, the LEDs 46 can directly emit light in the down direction past the lamp base 42. This is best shown by representative light ray 59 shown in
As mentioned above, the diffuser 48 can be arranged to disperse light from the phosphor carrier and LED into the desired lamp emission pattern, and can have many different shapes and sizes. In some embodiments, the diffuser also can be arranged over the phosphor carrier to mask the phosphor carrier when the lamp is not emitting. The diffuser can have materials to give a substantially white appearance to give the bulb a white appearance when the lamp is not emitting.
Many different diffusers with different shapes and attributes can be used with lamp 40 as well as the lamps described below, such as those described in U.S patent application Ser. No. 13/018,245, which is incorporated by reference above. This patent is titled “LED Lamp With Remote Phosphor and Diffuser Configuration”, and was filed on Jan. 31, 2011. The diffuser can also take different shapes, including but not limited to generally asymmetric “squat” as in U.S. patent application Ser. No. 12/901,405, titled “Non-uniform Diffuser to Scatter Light into Uniform Emission Pattern,” filed on Oct. 8, 2010, and incorporated herein by reference.
A reflective layer(s) or materials can also be included on surfaces of the heat sink structure 50 and on the heat pipe 44 to reflect light from the LEDs. In one embodiment, the top surface 58 of the heat sink structure 50 around the heat pipe 44 can comprise a reflective layer 60 that can be made of many different materials deposited and formed on the heat sink structure using known methods. These reflective layers 60 allow for the optical cavity to effectively recycle photons, and increase the emission efficiency of the lamp. In some embodiments the surfaces can be coated with a material having a reflectivity of approximately 75% or more to the lamp visible wavelengths of light emitted by the LEDs 46, while in other embodiments the material can have a reflectivity of approximately 85% or more to the LED light. In still other embodiments the material can have a reflectivity to the LED light of approximately 95% or more. It is understood that the reflective layer can comprise many different materials and structures including but not limited to reflective metals or multiple layer reflective structures such as distributed Bragg reflectors.
During operation of the lamp 40, an electrical signal from the connector 52 can be conducted to the power supply unit 55, and a drive signal can then be conducted to the LEDs 46 causing them to emit light. The signal from the power supply unit 55 can be conducted to the LEDs 46 using known conductors that can run to the LEDs along the heat pipe 44. In some embodiments a sleeve can be included around the heat pipe in which the conductors can run, with some sleeve embodiments having a reflective surface. In still other embodiments, a drive circuit or drive board (not shown) can be included between the power supply unit and the LEDs 46 to compensate for changes in LED emission over time and at different temperatures. This drive circuit can be in many different locations in the LED lamp 40 such as on the top surface 58 of the heat sink structure.
As the LEDs 46 emit light, they generate heat that can be conducted to the conductive block 56, and on to the top portion of the heat pipe 44. The heat pipe 44 then conducts heat to the lamp base 42 and its heat sink structure 50, where the heat can dissipate into the ambient. This provides efficient management of the heat generated by the LEDs 46, and allows for the LEDs to operate at cooler temperatures.
The lamp 100 also comprises a conductive block 102 that can be made of the same materials as conductive block 56 shown in
The heat sink structure 50 can also comprise heat fins 105 that radiate out from a center heat conductive core 106, with the heat fins 105 increasing the surface area for heat to dissipate. Heat from the heat pipe 44 spreads into the conductive core 106 and then spreads into the heat fins 105, where it spreads into the ambient. The heat fins 105 can take many different shapes and can be arranged in many different ways, with the heat fins 105 arranged vertically on the conductive core 106. The fins angle out and become larger moving up the heat sink structure 50 from the electrical connector 52, and then angle back toward the top of the heat sink structure 50. The lower portion can angle out in a way to allow LED lamp to fit within a particular lighting size envelope, such as A19 size envelopes. The fins angle back in to allow for light from the LEDs to emit down at the desired angle without being blocked be the fins 105.
The top of the fins 105 also comprise a slot 108 (best shown in
The different LED lamps according to the present invention can be arranged in many different ways, with many different features.
The LED lamp 150 also comprises a conductive block 158 that is mounted to the top of and in thermal contact with the heat pipe 44. The conductive block 158 is arranged such that its top surface 160 is available for mounting an LED 46. The conductive block 158 can accommodate LEDs 46 on its top surface 160 as well as its side surfaces 162. If each surface held a single LED 46, the block 158 can hold up to five LEDs, but it is understood that each surface can hold more than one LED.
As mentioned above, the heat pipes can be mounted to their lamp base using many different mechanisms and materials.
Embodiments of the present invention can be arranged in many different ways beyond those described above. By way of example,
Although the present invention has been described in detail with reference to certain preferred configurations thereof, other versions are possible. Therefore, the spirit and scope of the invention should not be limited to the versions described above.
