Abstract:
A solid-state light emitting diode (LED) lighting device is disclosed for use in general lighting. In the preferred embodiment, the LED lighting device comprises a heat sink having at least one opening, an output globe having at least one opening, and at least one ventilation channel. This channel helps to remove heat from the LED lighting device. An active cooling device is further installed inside the channel for very efficient heat removal. As a result, even at high luminous output, the LED lighting device is kept in a relatively small form factor. In some preferred embodiments, remote wavelength conversion luminescent phosphor particles or color mixing are utilized to achieve warm white lighting with high efficacy and high color rendering index (CRI). The LED lighting device has high luminous output, glare-free illumination, omni-directional distribution, and good color reproduction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. Provisional Patent Application No. 61/527,803 filed on Aug. 26, 2011, entitled “LED Lighting Device with Effective Heat Removal” which is incorporated herein by reference for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention generally relates to solid-state lighting devices, as well as related components, systems and methods, and more particularly to methods to make an LED light bulb with high luminous output and omni-directional distribution. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is well known that incandescent light bulbs are very inefficient in terms of energy utilization. About 90% of the electricity they consume is released as heat rather than light, and an even much smaller portion generates visible light. For lighting purpose, fluorescent light bulbs are about 10 times more efficient, and solid-state semiconductor light emitting diodes are about 20 times more efficient. 
         [0004]    Because solid-state semiconductor light emitters are environmentally friendly and have a big potential in energy saving and long operation life in comparison with traditional lighting devices, solid-state light emitting apparatus are being widely designed and marketed as replacements for conventional incandescent lighting apparatus. There have been considerable efforts to replace incandescent light bulb using solid-state LEDs. However, most of the existing LED light bulbs suffer at least one of the following shortcomings: 
         [0005]    Today&#39;s LED light bulbs can only deliver up to 850 lumens in a form factor equivalent to the output of 60 W incandescent light bulbs. Although tremendous progress has been made to improve the light emission efficiency of solid-state LEDs in the past 20 years, as of today, they only manage to covert less than 20% electrical power into visible light, while the rest is still being released as heat. Unlike an incandescent light bulb that can effectively dissipate heat through radiation, LEDs mainly rely on conduction and convection by using heat sinks for heat removal. As the luminous output increases, the required heat sink volume has to increase to keep the LEDs operating within an acceptable temperature range. As a result, the LED lighting apparatus becomes very bulky. It is a daunting challenge for LED lighting devices to deliver an equivalent luminous output in a size comparable to incandescent light bulbs. 
         [0006]    The LED sources are usually mounted on a PCB board that resides in the center area of the LED light bulb and within an enclosure inside the LED light bulb. There is a relatively long path for the heat to travel to the outer surface of the heat sink. As a result, the thermal resistance is so high as to cause high junction temperature in LEDs. Running an LED at elevated temperature reduces its emission efficiency and its operation life due to degradation and premature failures. 
         [0007]    The LEDs known in the art extract the light in a forward direction. Although they can have a far field distribution as wide as up to 180 degrees, most general lighting applications require near omni-directional (more than 300 degrees) light distribution. Most existing LED light bulb can only manage to deliver a light distribution of about 180 degrees. Moreover, most of the existing LED light bulbs do not have a shape and form factor that closely match consumer preferences for an incandescent light bulb&#39;s look and feel. The expectation of the consumers remains unmet. 
         [0008]    To facilitate better thermal management and combat issues such as glare and multiple source shadow, most existing LED light bulbs use a relatively large number of LEDs with relatively smaller chip size, which are run at relatively lower current. This approach makes the LED light bulb relatively bulky and less reliable, as well as increases both material cost and manufacturing cost. 
         [0009]    There is a need for an improved LED light bulb that delivers omni-directional distribution with high luminous efficacy, high luminous output, and reduced cost in a shape and form factor comparable to incandescent light bulbs. 
       SUMMARY OF THE INVENTION 
       [0010]    The need is met by the present new, useful, and non-obvious invention. 
         [0011]    While various shapes of the lighting devices are within the scope of the present invention, the preferred embodiment of the present invention has a shape and form factor resembling the incandescent light bulb. In a particular preferred embodiment, the combined shape of the heat sink and the output globe forms a standard A19 light bulb shape. 
         [0012]    In one preferred embodiment, the LED lighting device of the present invention comprises an electrical connector, an electrical AC/DC conversion and control driver, a driver housing, a heat sink, a plurality of semiconductor light emitting diodes (LEDs), a reflective cap, an air pipe, and an output globe. The heat sink and the air pipe form a channel substantially around the centerline of the LED lighting device. Both the output globe and the heat sink have openings to provide air intake or exhaust for the channel. When the lighting device is turned on, the heat generated by the LEDs and the driver will heat the air inside the channel, and the warm air rises and creates a convective force. This convective force will help move the air through the channel and remove heat from the lighting devices. In another preferred embodiment, the LED lighting device of the present invention uses an active cooling device such as a cooling fan or a synthetic jet inside the channel to introduce forced convection for further improvement of heat removal. These arrangements reduce the required heat sink volume greatly. Therefore, the lighting device with high luminous output can still have a form and shape factor similar to traditional incandescent lighting apparatus. 
         [0013]    The electrical power connector of the lighting device may be a standard Edison-type screw connector such that the lighting device can be used to replace a standard incandescent light bulb. 
         [0014]    The heat sink, according to the preferred embodiment of the present invention, has a cylindrical main body with fins on its outside surface for heat dissipation. Inside the heat sink, a cutout substantially around the centerline in the upper portion forms an upper housing to host the electronics, which include the electrical AC/DC conversion and control driver and the active cooling device if used. The heat sink has a frustum extended down from its cylindrical main body. This frustum has a plurality of side surfaces. The LEDs are mounted on these side surfaces and emit light outwards and slightly downwards. Inside the frustum, there is a hole connecting the frustum&#39;s top surface to the cutout in the upper portion so that a tunnel is formed substantially around the centerline of the heat sink. An air channel is then formed after attaching the air pipe to the frustum&#39;s opening. 
         [0015]    The output globe according to the preferred embodiment of the present invention has a hemisphere shape with a diameter larger than the diameter of the heat sink&#39;s main cylindrical body. Also, the upper portion of the output globe is shaped in such a way that its opening can have a tight fit with the heat sink&#39;s main cylindrical body. Together with the air pipe, the output globe and the heat sink form an airtight space surrounding the LEDs. In one preferred embodiment, the output globe is made of translucent material with a substantial amount of light being diffusively reflected. Part of the reflected light will be recycled by the reflective cap. A substantial portion of the reflected light will go through the gaps between the fins to reach the upper hemisphere so that omni-directional lighting is realized. In some other preferred embodiments, the output globe comprises two separate pieces: the upper cover and the lower globe. The upper cover is made of substantially transparent material, while the lower globe is made of translucent material with a substantial amount of light being diffusively reflected. Part of the reflected light will be recycled by the reflective cap. A substantial portion of the reflected light will go through the upper cover and the gaps between the fins to reach the upper hemisphere. Therefore, omni-directional lighting is realized 
         [0016]    The LED typically consists of a light-emitting element called the LED die or LED chip, a chip carrier called the sub-mount, electrical leads, a thermal conductive pad, and a lens. The sub-mount is usually thermally conductive but electrically non-conductive. More than one LED chip can be packaged into the same sub-mount as well. The LEDs are commercially available from a number of manufacturers, such as Cree, Philips Lumileds, and Osram. These manufacturers also supply LEDs with or without phosphors included in the package. Cool white light LEDs and warm white light LEDs are commercially available from Cree, Philip Lumileds, Osram, etc. These LEDs can be used in the present invention to produce a complete LED lighting device with color rendering index (CRI) specified by the LED vendors. The LED lighting device of the present invention may utilize a few groups of LEDs to achieve the desired color rendering index (CRI) in some embodiments, with each group of LEDs emitting a different dominant wavelength. Different colors of light are mixed within the output globe. 
         [0017]    There have been extensive studies on achieving warm white light using blue LEDs or near-UV LEDs in combination with remote phosphors. Blue light LEDs or near-UV LEDs are commercially available from Cree, Philip Lumileds, Osram, etc. In some preferred embodiments of the present invention, these LEDs can be used together with the remote phosphor caps to produce a complete LED lighting device with high color rendering index (CRI). These remote phosphor caps are made of substantially transparent plastic material that is embedded with wavelength conversion luminescent phosphor particles. In some other embodiments, the LED lighting device of the present invention may utilize a first group of blue or UV LEDs that are capped by the remote phosphor caps, and a second group of green or red LEDs. This second group of green or red LEDs are to make up for the color deficiency of the light emerging from the remote phosphor caps. Different colors of light are mixed within the output globe. As a result, high color rendering index (CRI) is achieved. 
         [0018]    Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  illustrates the preferred shape of the LED lighting device according to the present invention. 
           [0020]      FIG. 2  is the exploded view of a preferred embodiment of the LED lighting device according to the present invention. 
           [0021]      FIG. 3  is the cross section view of an LED lighting device according to the present invention. 
           [0022]      FIG. 4   a  and  FIG. 4   b  illustrate the heat sink of a preferred embodiment according to the present invention viewed from two different angles. 
           [0023]      FIG. 5   a  illustrates the air pipe of a preferred embodiment according to the present invention. 
           [0024]      FIG. 5   b  illustrates the reflective cap of a preferred embodiment according to the present invention. 
           [0025]      FIG. 6   a  illustrates the output globe in some of the preferred embodiments according to the present invention. 
           [0026]      FIG. 6   b  illustrates the output globe comprising two pieces in some other preferred embodiments according to the present invention. 
           [0027]      FIG. 7  is the side view of a typical LED. 
           [0028]      FIG. 8  illustrates the preferred shape of a first embodiment of the LED lighting device according to the present invention. 
           [0029]      FIG. 9  is the exploded view of a first embodiment of the LED lighting device according to the present invention: without remote phosphor and active cooling device. 
           [0030]      FIG. 10  illustrates the preferred shape of a second embodiment of the LED lighting device according to the present invention. 
           [0031]      FIG. 11  is the exploded view of a second embodiment of the LED lighting device according to the present invention: without remote phosphor and with active cooling device. 
           [0032]      FIG. 12  is the side view of a typical LED mounted on the heat sink with a small blocking mirror attached. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Embodiments of the invention are described herein with reference to schematic illustrations of embodiments of the invention. 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 techniques and/or tolerances. 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. 
         [0034]    The present invention will now be described with reference to  FIG. 1 . While various shapes of the lighting devices are within the scope of the present invention, the preferred embodiment of the present invention has a shape and form factor closely resembling the incandescent light bulb. In a particular embodiment, the combined shape of the heat sink and the output globe forms a standard A19 light bulb shape  100 . 
         [0035]    As illustrated in  FIG. 2  and  FIG. 3 , in one of the preferred embodiments, the LED lighting device  100  of the present invention comprises an electrical connector  10 , an electrical AC/DC conversion and control driver  20 , a driver housing  21 , a heat sink  40 , a plurality of semiconductor light emitting diodes (LEDs)  50 , a reflective cap  60 , a plurality of remote phosphor caps  70 , an air pipe  80 , and an output globe  90 . The heat sink  40  and the air pipe  80  form a channel  101  substantially around the centerline of the LED lighting device  100 . The output globe  90  has an opening  91  and the heat sink  40  has a plurality of openings  49  to provide air intake or exhaust for the channel  101 . When the lighting device is turned on, the heat generated by the LEDs  50  and the driver  20  will heat the air inside the channel  101 , and the warm air rises and creates a convective force. This convective force will help move the air through the channel  101  and remove heat from the lighting devices  100 . In another preferred embodiment, the LED lighting device  100  of the present invention uses an active cooling device  30  such as a cooling fan or a synthetic jet inside the channel  101  to introduce forced convection for further improvement of heat removal. These arrangements reduce the required heat sink volume greatly. Therefore, the lighting device  100  with high luminous output can still have a form and shape factor similar to traditional incandescent lighting apparatus. 
         [0036]    The electrical power connector  10  of the lighting device may be a standard Edison-type screw connector such that the lighting device can be used to replace a standard incandescent light bulb. 
         [0037]      FIG. 4   a  and  FIG. 4   b  illustrate the heat sink  40  according to the preferred embodiment of the present invention viewed from two different angles. The heat sink  40  has a cylindrical main body  41  with fins  42  on its outside surface for heat dissipation. Near its upper edge, the heat sink  40  has a plurality of openings  49 . Inside the heat sink  40 , a cutout substantially around the centerline in the upper portion forms an upper housing  43  to host the electronics, which include the electrical AC/DC conversion and control driver  20  and its housing  21 , and the active cooling device  30  if used. The heat sink  40  has a frustum  44  extended down from its cylindrical main body  41 . This frustum  44  has a plurality of side surfaces  45 . The LEDs are mounted on these side surfaces and emit light outwards and slightly downwards. Inside the frustum  44 , there is a through-hole  46  connecting the frustum&#39;s top surface to the upper housing  43  so that a tunnel is formed substantially around the centerline of the heat sink  40 . An air channel is then formed after attaching the air pipe  80  to the frustum&#39;s opening. The contour diameter of the fins  42  gradually increases starting from the heat sink&#39;s upper edge to the base of the frustum  44  to form a pear contour shape. A ring  47  connects all the fins  42  at the lower end around the base of the frustum  44 . The ring  47  can facilitate easy handling of the lighting device. The gaps  48  between the heat sink&#39;s main body  41  and the ring  47  allow light to pass through to reach a substantially large portion of the upper hemisphere of the lighting device. It is further understood that the through-hole  46  can be cut with many different hole opening sizes and shapes including circular, oval, rectangular, hexagonal, star or other multiple side shapes. In general, the bigger the surface area, the better the convective heat dissipation. 
         [0038]    As illustrated in  FIG. 5   a , the air pipe  80  according to the preferred embodiment of the present invention is a thin pipe that can have a variety of cross-section shapes  81 , including circular, oval, rectangular, hexagonal, star or other multiple side shapes. It has a relatively small cross-section size so that it will not form any light shadows. The air pipe  80  can be made of either thermally conductive material such as metals, or thermally non-conductive materials such as plastics, with its outside surfaces coated with highly reflective paint. The air pipe  80  has a tight fit with the output globe&#39;s opening  91  and the through-hole  46  of the heat sink&#39;s frustum.  44 . 
         [0039]    As illustrated in  FIG. 6   a , in some of the preferred embodiments of the present invention, the output globe  90  has a hemisphere shape with a diameter larger than the diameter of the heat sink&#39;s main cylindrical body  41 , but roughly equal to the diameter of the handling ring  47 . Also, the upper portion of the output globe is shaped in such a way that its upper opening  92  can have a tight fit with the heat sink&#39;s main cylindrical body  41  near the base of the frustum  44 . At the bottom of the output globe  90 , there is another opening  91  that provides air passage for the air channel  101 . It is further understood that the opening  91  can be cut with many different hole opening sizes and shapes including circular, oval, rectangular, hexagonal, star or other multiple side shapes. Together with the air pipe  80 , the output globe  90  and the heat sink  40  form an airtight space surrounding the LEDs  50 . The output globe  90  is made of translucent material with a substantial amount of light being diffusively reflected. Part of the reflected light will be recycled by the reflective cap  60 . A substantial portion of the reflected light will go through the gaps  48  between the fins  42  to reach the upper hemisphere so that omni-directional lighting is realized. 
         [0040]    As illustrated in  FIG. 6   b , in some other preferred embodiments of the present invention, the output globe  90  comprises two separate pieces: the upper cover  93  and the lower globe  94 . The upper cover  93  and the lower globe  94  have a tight fit. The upper cover  93  is made of substantially transparent material, while the lower globe  94  is made of translucent material with a substantial amount of light being diffusively reflected. Part of the reflected light will be recycled by the reflective cap  60 . A substantial portion of the reflected light will go through the upper cover  93  and the gaps  48  between the fins  42  to reach the upper hemisphere. Therefore, omni-directional lighting is realized. In some other embodiments of the present invention, both the upper cover  93  and the lower globe  94  can be made of substantially transparent material with light diffusing features on their surfaces, such as light shaping diffusers based on holography technology. 
         [0041]      FIG. 7  illustrates a typical LED  50 . The LED  50  typically consists of a light-emitting element called the LED die or LED chip  51 , a chip carrier called sub-mount  52 , an electrical lead anode  53 , an electrical lead cathode  54 , a thermal pad  55 , and a lens  56 . The sub-mount  52  is usually thermally conductive but electrically non-conductive. More than one LED chip can be packaged into the same sub-mount as well. The LEDs are commercially available from a number of manufacturers, such as Cree, Philips Lumileds, and Osram. These manufacturers also supply LEDs with or without phosphors included in the package. Cool white light LEDs and warm white light LEDs that have phosphors embedded in the lens material are commercially available from Cree, Philip Lumileds, Osram, etc. These LEDs can be used in the present invention to produce a complete LED lighting device with color rendering index (CRI) specified by the LED vendors. In some other ways to achieve desired high color rendering index (CRI), the LED lighting device of the present invention may utilize a few groups of LEDs in some embodiments, with each group of LEDs emitting a different dominant wavelength. Different colors of light are mixed within the output globe. 
         [0042]    As illustrated in  FIG. 5   b , the reflective cap  60  is a thin cap with a shape closely matching the frustum  44  of the heat sink  40 . It has a plurality of openings  61  that have tight fits with the output lens  56  of the LEDs  50 . It also has an opening  62  that has a tight fit with the air pipe  80 . The reflective cap  60  is made of highly reflective material, or has highly reflective material coated on its outside side surfaces  63 . The reflective cap  60  sits right on top of the heat sink&#39;s frustum  44 . 
         [0043]    There have been extensive studies on achieving warm white light using blue LEDs or near-UV LEDs in combination with remote phosphors. Blue light LEDs or near-UV LEDs are commercially available from Cree, Philip Lumileds, Osram, etc. In some preferred embodiments of the present invention, these LEDs can be used together with the remote phosphor caps  70  to produce a complete LED lighting device with high color rendering index (CRI). These remote phosphor caps are made of substantially transparent plastic material that is embedded with phosphor particles. In some other embodiments, the LED lighting device of the present invention may utilize a first group of blue or UV LEDs that is capped by the remote phosphor caps, and a second group of green or red LEDs. This second group of green or red LEDs is to make up for the color deficiency of the light emerging from the remote phosphor caps  70 . Different colors of light are mixed within the output globe. As a result, high color rendering index (CRI) is achieved. 
         [0044]    The preferred embodiments of the present invention will now be described with reference to  FIG. 8 ,  FIG. 9  and other sub-component or module drawings from  FIG. 4   a  to  FIG. 7 . In a first preferred embodiment of the present invention, the LED lighting device  100  comprises an electrical connector  10 , an electrical AC/DC conversion and control driver  20 , a driver housing  21 , a heat sink  40 , a plurality of semiconductor light emitting diodes (LEDs)  50 , a reflective cap  60 , an air pipe  80 , and an output globe  90 . The heat sink  40  and the air pipe  80  form a channel  101  substantially around the centerline of the LED lighting device  100 . The output globe  90  has an opening  91  and the heat sink  40  has a plurality of openings  49  to provide air intake or exhaust for the channel  101 . The LEDs  50  are the cool white light LEDs or warm white light LEDs that have phosphors embedded in the lens material, commercially available from Cree, Philip Lumileds, Osram, etc. The lighting devices  100  will have a color rendering index (CRI) equal to the CRI of the LEDs  50  specified by the LED vendors. The heat sink  40  has a cylindrical main body  41  with fins  42  on its outside surface for heat dissipation. There are a plurality of openings  49  around the upper edge of the heat sink  40  that provides openings for the air channel  101 . Inside the heat sink  40 , a cutout substantially around the centerline in the upper portion forms an upper housing  43  to host the electronics, which include the electrical AC/DC conversion and control driver  20  and its housing  21 . The heat sink  40  has a frustum  44  extended down from its cylindrical main body  41 . This frustum  44  has a plurality of side surfaces  45 . The LEDs are mounted on these side surfaces and emit light outwards and slightly downwards. Inside the frustum  44 , there is a through-hole  46  connecting the frustum&#39;s top surface to the upper housing  43  so that a tunnel is formed substantially around the centerline of the heat sink  40 . An air channel  101  is then formed after attaching the air pipe  80  to the frustum&#39;s opening. The contour diameter of the fins  42  gradually increases starting from the heat sink&#39;s upper edge to the base of the frustum  44  to form a pear contour shape. A ring  47  connects all the fins  42  at the lower end around the base of the frustum  44 . The ring  47  can facilitate easy handling of the lighting device. The gaps  48  between the heat sink&#39;s main body  41  and the ring  47  allow light to pass through to reach a substantially large portion of the upper hemisphere of the lighting device, so that omni-directional light is realized. When the lighting device  100  is turned on, the heat generated by the LEDs  50  and the driver  20  will heat the air inside the channel  101 , and the warm air rises and creates a convective force. This convective force will help move the air through the channel  101  and remove heat from the lighting devices  100 . The output globe  90  has a hemisphere shape with a diameter larger than the diameter of the heat sink&#39;s main cylindrical body  41 , but roughly equal to the diameter of the handling ring  47 . Also, the upper portion of the output globe is shaped in such a way that its upper opening  92  can have a tight fit with the heat sink&#39;s main cylindrical body  41  near the base of the frustum  44 . At the bottom of the output globe  90 , there is another opening  91  that provides air passage for the air channel  101 . Together with the air pipe  80 , the output globe  90  and the heat sink  40  form an airtight space surrounding the LEDs  50 . The output globe  90  is made of translucent material with a substantial amount of light being diffusively reflected. The reflective cap  60  will recycle part of the reflected light. A substantial portion of the reflected light will go through the gaps  48  between the fins  42  to reach the upper hemisphere so that omni-directional lighting is realized. 
         [0045]    As illustrated in  FIG. 10 ,  FIG. 11  and other sub-component and module drawings from  FIG. 4   a  to  FIG. 7 , in a second preferred embodiment of the present invention, the LED lighting device  100  comprises an electrical connector  10 , an electrical AC/DC conversion and control driver  20 , a driver housing  21 , a heat sink  40 , a plurality of semiconductor light emitting diodes (LEDs)  50 , a reflective cap  60 , an air pipe  80 , and an output globe  90 . The heat sink  40  and the air pipe  80  form a channel  101  substantially around the centerline of the LED lighting device  100 . The output globe  90  has an opening  91  and the heat sink  40  has a plurality of openings  49  to provide air intake or exhaust for the channel  101 . The LEDs  50  are the cool white light LEDs or warm white light LEDs that have phosphors embedded in the lens material, commercially available from Cree, Philip Lumileds, Osram, etc. The lighting devices  100  will have a color rendering index (CRI) equal to the CRI of the LEDs  50  specified by the LED vendors. The heat sink  40  has a cylindrical main body  41  with fins  42  on its outside surface for heat dissipation. Inside the heat sink  40 , a cutout substantially around the centerline in the upper portion forms an upper housing  43  to host the electronics, which include the electrical AC/DC conversion and control driver  20  and its housing  21 . The heat sink  40  has a frustum  44  extended down from its cylindrical main body  41 . This frustum  44  has a plurality of side surfaces  45 . The LEDs  50  are mounted on these side surfaces and emit light outwards and slightly downwards. Inside the frustum  44 , there is a through-hole  46  connecting the frustum&#39;s top surface to the upper housing  43  so that a tunnel is formed substantially around the centerline of the heat sink  40 . An air channel  101  is then formed after attaching the air pipe  80  to the frustum&#39;s opening. The contour diameter of the fins  42  gradually increases starting from the heat sink&#39;s upper edge to the base of the frustum  44  to form a pear contour shape. A ring  47  connects all the fins  42  at the lower end around the base of the frustum  44 . The ring  47  can facilitate easy handling of the lighting device. The gaps  48  between the heat sink&#39;s main body  41  and the ring  47  allow light to pass through to reach a substantially large portion of the upper hemisphere of the lighting device, so that omni-directional light is realized. When the lighting device is turned on, the heat generated by the LEDs  50  and the driver  20  will heat the air inside the channel  101 , and the warm air rises and creates a convective force. This convective force will help move the air through the channel  101  and remove heat from the lighting devices  100 . An active cooling device  30  such as a cooling fan or a synthetic jet is installed between the housing  21  and the frustum  44  inside the channel  101  to introduce forced convection for further improvement of heat removal. These arrangements reduce the required heat sink volume greatly. Therefore, the lighting device  100  with high luminous output can still have a form and shape factor similar to traditional incandescent lighting apparatus. The output globe  90  has a hemisphere shape with a diameter larger than the diameter of the heat sink&#39;s main cylindrical body  41 , but roughly equal to the diameter of the handling ring  47 . Also, the upper portion of the output globe is shaped in such a way that its upper opening  92  can have a tight fit with the heat sink&#39;s main cylindrical body  41  near the base of the frustum  44 . At the bottom of the output globe  90 , there is another opening  91  that provides air passage for the air channel  101 . Together with the air pipe  80 , the output globe  90  and the heat sink  40  form an airtight space surrounding the LEDs  50 . The output globe  90  is made of translucent material with a substantial amount of light being diffusively reflected. The reflective cap  60  will recycle part of the reflected light. A substantial portion of the reflected light will go through the gaps  48  between the fins  42  to reach the upper hemisphere so that omni-directional lighting is realized. 
         [0046]    In a third preferred embodiment of the present invention, all other arrangements are identical to the first embodiment described earlier, except that the output globe  90  comprises two separate pieces: the upper cover  93  and the lower globe  94 . The upper cover  93  and the lower globe  94  have a tight fit. The upper cover  93  is made of substantially transparent material, while the lower globe  94  is made of translucent material with a substantial amount of light being diffusively reflected. As illustrated in  FIG. 12 , to make sure no light can escape from the output globe  90  without at least being diffusely reflected at least once, a small mirror  57  is positioned right beside the LED  50  to deflect some of the light. 
         [0047]    In a fourth preferred embodiment of the present invention, all other arrangements are identical to the second embodiment described earlier, except that the output globe  90  comprises two separate pieces: the upper cover  93  and the lower globe  94 . The upper cover  93  and the lower globe  94  have a tight fit. The upper cover  93  is made of substantially transparent material, while the lower globe  94  is made of translucent material with a substantial amount of light being diffusively reflected. As illustrated in  FIG. 12 , to make sure no light can escape from the output globe  90  without being diffused at least once, a small mirror  57  is positioned right beside the LED  50  to deflect some of the light. 
         [0048]    As illustrated in  FIG. 10 ,  FIG. 11  and other sub-component and module drawings from  FIG. 4   a  to  FIG. 7 , in a fifth preferred embodiment of the present invention, the LED lighting device  100  comprises an electrical connector  10 , an electrical AC/DC conversion and control driver  20 , a driver housing  21 , a heat sink  40 , a plurality of semiconductor light emitting diodes (LEDs)  50 , a reflective cap  60 , an air pipe  80 , and an output globe  90 . The heat sink  40  and the air pipe  80  form a channel  101  substantially around the centerline of the LED lighting device  100 . The output globe  90  has an opening  91  and the heat sink  40  has a plurality of openings  49  to provide air intake or exhaust for the channel  101 . The LEDs  50  comprise two groups: a plurality first group of cool white LEDs  50  that lack red light component and a plurality second group of red LEDs  50  that emit light with a dominant wavelength around 630 nm. The two groups of LEDs  50  are mounted in such a way that different colors of light can be effectively mixed within the output globe  90  to achieve desired high color rendering index (CRI). The heat sink  40  has a cylindrical main body  41  with fins  42  on its outside surface for heat dissipation. Inside the heat sink  40 , a cutout substantially around the centerline in the upper portion forms an upper housing  43  to host the electronics, which include the electrical AC/DC conversion and control driver  20  and its housing  21 . The heat sink  40  has a frustum  44  extended down from its cylindrical main body  41 . This frustum  44  has a plurality of side surfaces  45 . The LEDs are mounted on these side surfaces and emit light outwards and slightly downwards. Inside the frustum  44 , there is a through-hole  46  connecting to the upper housing  43  so that a tunnel is formed substantially around the centerline of the heat sink  40 . An air channel  101  is then formed after attaching the air pipe  80  to the frustum&#39;s opening. The contour diameter of the fins  42  gradually increases starting from the heat sink&#39;s upper edge to the base of the frustum  44  to form a pear contour shape. A ring  47  connects all the fins  42  at the lower end around the base of the frustum  44 . The ring  47  can facilitate easy handling of the lighting device. The gaps  48  between the heat sink&#39;s main body  41  and the ring  47  allow light to pass through to reach a substantially large portion of the upper hemisphere of the lighting device, so that omni-directional lighting is realized. When the lighting device is turned on, the heat generated by the LEDs  50  and the driver  20  will heat the air inside the channel  101 , and the warm air rises and creates a convective force. This convective force will help move the air through the channel  101  and remove heat from the lighting devices  100 . An active cooling device  30  such as a cooling fan or a synthetic jet is installed between the housing  21  and the frustum  44  inside the channel  101  to introduce forced convection for further improvement of heat removal. These arrangements reduce the required heat sink volume greatly. Therefore, the lighting device  100  with high luminous output can still have a form and shape factor similar to traditional incandescent lighting apparatus. The output globe  90  has a hemisphere shape with a diameter larger than the diameter of the heat sink&#39;s main cylindrical body  41 , but roughly equal to the diameter of the handling ring  47 . Also, the upper portion of the output globe is shaped in such a way that its upper opening  92  can have a tight fit with the heat sink&#39;s main cylindrical body  41  near the base of the frustum  44 . At the bottom of the output globe  90 , there is another opening  91  that provides air passage for the air channel  101 . Together with the air pipe  80 , the output globe  90  and the heat sink  40  form an airtight space surrounding the LEDs  50 . The output globe  90  is made of translucent material with a substantial amount of light being diffusively reflected. The reflective cap  60  will recycle part of the reflected light. A substantial portion of the reflected light will go through the gaps  48  between the fins  42  to reach the upper hemisphere so that omni-directional lighting is realized. 
         [0049]    As illustrated in  FIG. 10 ,  FIG. 11  and other sub-component drawings from  FIG. 4   a  to  FIG. 7 , in a sixth preferred embodiment of the present invention, the LED lighting device  100  comprises an electrical connector  10 , an electrical AC/DC conversion and control driver  20 , a driver housing  21 , a heat sink  40 , a plurality of semiconductor light emitting diodes (LEDs)  50 , a reflective cap  60 , an air pipe  80 , and an output globe  90 . The heat sink  40  and the air pipe  80  form a channel  101  substantially around the centerline of the LED lighting device  100 . The output globe  90  has an opening  91  and the heat sink  40  has a plurality of openings  49  to provide air intake or exhaust for the channel  101 . The LEDs  50  comprise two groups: a plurality first group of LEDs  50  that has red phosphor embedded in their lens material but lack green light component, and a plurality second group of green LEDs  50  that emit light with a dominant wavelength around 570 nm. The two groups of LEDs  50  are mounted on the frustum&#39;s side surfaces in such a way that different colors of light can be effectively mixed within the output globe  90  to achieve desired high color rendering index (CRI). The heat sink  40  has a cylindrical main body  41  with fins  42  on its outside surface for heat dissipation. Inside the heat sink  40 , a cutout substantially around the centerline in the upper portion forms an upper housing  43  to host the electronics, which include the electrical AC/DC conversion and control driver  20  and its housing  21 . The heat sink  40  has a frustum  44  extended down from its cylindrical main body  41 . This frustum  44  has a plurality of side surfaces  45 . The LEDs are mounted on these side surfaces and emit light outwards and slightly downwards. Inside the frustum  44 , there is a through-hole  46  connecting to the upper housing  43  so that a tunnel is formed substantially around the centerline of the heat sink  40 . An air channel  101  is then formed after attaching the air pipe  80  to the frustum&#39;s opening. The contour diameter of the fins  42  gradually increases starting from the heat sink&#39;s upper edge to the base of the frustum  44  to form a pear contour shape. A ring  47  connects all the fins  42  at the lower end around the base of the frustum  44 . The ring  47  can facilitate easy handling of the lighting device. The gaps  48  between the heat sink&#39;s main body  41  and the ring  47  allow light to pass through to reach a substantially large portion of the upper hemisphere of the lighting device, so that omni-directional lighting is realized. When the lighting device is turned on, the heat generated by the LEDs  50  and the driver  20  will heat the air inside the channel  101 , and the warm air rises and creates a convective force. This convective force will help move the air through the channel  101  and remove heat from the lighting devices  100 . An active cooling device  30  such as a cooling fan or a synthetic jet is installed between the housing  21  and the frustum  44  inside the channel  101  to introduce forced convection for further improvement of heat removal. These arrangements reduce the required heat sink volume greatly. Therefore, the lighting device  100  with high luminous output can still have a form and shape factor similar to traditional incandescent lighting apparatus. The output globe  90  has a hemisphere shape with a diameter larger than the diameter of the heat sink&#39;s main cylindrical body  41 , but roughly equal to the diameter of the handling ring  47 . Also, the upper portion of the output globe is shaped in such a way that its upper opening  92  can have a tight fit with the heat sink&#39;s main cylindrical body  41  near the base of the frustum  44 . At the bottom of the output globe  90 , there is another opening  91  that provides air passage for the air channel  101 . Together with the air pipe  80 , the output globe  90  and the heat sink  40  form an airtight space surrounding the LEDs  50 . The output globe  90  is made of translucent material with a substantial amount of light being diffusively reflected. The reflective cap  60  will recycle part of the reflected light. A substantial portion of the reflected light will go through the gaps  48  between the fins  42  to reach the upper hemisphere so that omni-directional lighting is realized. 
         [0050]    As illustrated in  FIG. 1 ,  FIG. 2 ,  FIG. 3  and other sub-component drawings from  FIG. 4   a  to  FIG. 7 , in a seventh preferred embodiment of the present invention, the LED lighting device  100  comprises an electrical connector  10 , an electrical AC/DC conversion and control driver  20 , a driver housing  21 , a heat sink  40 , a plurality of semiconductor light emitting diodes (LEDs)  50 , a reflective cap  60 , a plurality of phosphor caps  70 , an air pipe  80 , and an output globe  90 . The heat sink  40  and the air pipe  80  form a channel  101  substantially around the centerline of the LED lighting device  100 . The output globe  90  has an opening  91  and the heat sink  40  has a plurality of openings  49  to provide air intake or exhaust for the channel  101 . The LEDs  40  are blue LEDs with dominant wavelength around 450 nm to 460 nm. The phosphor caps  70  are embedded with phosphors that convert the blue light into warm white light with high color rendering index (CRI). These phosphor caps  70  cover the blue LEDs  40  and attached to the reflective cap  60 . The heat sink  40  has a cylindrical main body  41  with fins  42  on its outside surface for heat dissipation. Inside the heat sink  40 , a cutout substantially around the centerline in the upper portion forms an upper housing  43  to host the electronics, which include the electrical AC/DC conversion and control driver  20  and its housing  21 . The heat sink  40  has a frustum  44  extended down from its cylindrical main body  41 . This frustum  44  has a plurality of side surfaces  45 . The LEDs are mounted on these side surfaces and emit light outwards and slightly downwards. Inside the frustum  44 , there is a through-hole  46  connecting to the upper housing  43  so that a tunnel is formed substantially around the centerline of the heat sink  40 . An air channel  101  is then formed after attaching the air pipe  80  to the frustum&#39;s opening. The contour diameter of the fins  42  gradually increases starting from the heat sink&#39;s upper edge to the base of the frustum  44  to form a pear contour shape. A ring  47  connects all the fins  42  at the lower end around the base of the frustum  44 . The ring  47  can facilitate easy handling of the lighting device. The gaps  48  between the heat sink&#39;s main body  41  and the ring  47  allow light to pass through to reach a substantially large portion of the upper hemisphere of the lighting device, so that omni-directional lighting is realized. When the lighting device is turned on, the heat generated by the LEDs  50  and the driver  20  will heat the air inside the channel  101 , and the warm air rises and creates a convective force. This convective force will help move the air through the channel  101  and remove heat from the lighting devices  100 . An active cooling device  30  such as a cooling fan or a synthetic jet is installed between the housing  21  and the frustum  44  inside the channel  101  to introduce forced convection for further improvement of heat removal. These arrangements reduce the required heat sink volume greatly. Therefore, the lighting device  100  with high luminous output can still have a form and shape factor similar to traditional incandescent lighting apparatus. The output globe  90  has a hemisphere shape with a diameter larger than the diameter of the heat sink&#39;s main cylindrical body  41 , but roughly equal to the diameter of the handling ring  47 . Also, the upper portion of the output globe is shaped in such a way that its upper opening  92  can have a tight fit with the heat sink&#39;s main cylindrical body  41  near the base of the frustum  44 . At the bottom of the output globe  90 , there is another opening  91  that provides air passage for the air channel  101 . Together with the air pipe  80 , the output globe  90  and the heat sink  40  form an airtight space surrounding the LEDs  50 . The output globe  90  is made of translucent material with a substantial amount of light being diffusively reflected. The reflective cap  60  will recycle part of the reflected light. A substantial portion of the reflected light will go through the gaps  48  between the fins  42  to reach the upper hemisphere so that omni-directional lighting is realized. 
         [0051]    Although the present invention is illustrated in connection with specific embodiments for instructional purposes, the present invention is not limited thereto. Various combinations, adaptations and modifications may be made without departing from the scope of the invention. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description. 
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