Abstract:
Disclosed herein are embodiments of LED-based lights for use in fluorescent fixtures that emanate light in a plurality of directions. One embodiment disclosed herein of an LED light for use in a fluorescent light fixture comprises a housing and a circuit board having a first surface configured to face an illumination area, the circuit board mounted in the housing and defining a plane conceptually dividing the housing into a first portion and a second portion. At least one LED is mounted on the first surface of the circuit board and is configured to emanate light in a first direction. Light distribution means is configured to distribute a portion of the light emanated in the first direction to at least a second direction different than the first direction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to Provisional Application No. 61/317,825 filed Mar. 26, 2010, which is hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a light emitting diode (LED) based light tube usable in a fluorescent light fixture in place of a conventional fluorescent tube. 
       BACKGROUND 
       [0003]    Fluorescent tubes are widely used in a variety of locations such as schools and office buildings for providing area lighting, for example. A fluorescent tube typically produces an even distribution of light about its circumference. However, the circumferentially uniform light produced by typical fluorescent tubes may be modified after exiting the tube such that the light distribution becomes directional with a greater amount of light directed in a first radial direction compared to a second radial direction. 
         [0004]    Consider the example of a fluorescent light fixture installed in a ceiling. The light produced by a fluorescent tube installed in such a fixture is typically intended to illuminate an area below the ceiling. A reflector is often positioned above the fluorescent tube to redirect upward traveling light toward the area below the ceiling to be illuminated. The reflector can in effect increase the efficiency of the fluorescent tube by redirecting light that would otherwise illuminate an area where illumination provides limited or no benefit, such as a portion of the ceiling above the fluorescent tube in the present example, toward an area where illumination provides a greater benefit. Reflectors used to make light produced by fluorescent tubes directional are present in many existing fluorescent tube fixtures. 
         [0005]    LED-based light tubes have been developed for use in fluorescent light fixtures to replace conventional fluorescent tubes. LED-based light tubes, by definition, each include one or more LEDs. LEDs output light directionally, typically in a Lambertian distribution. A typical LED-based tube is constructed with its LEDs arranged to face in a common direction. As such, the typical LED-based tube should be installed in a fixture in a specific orientation, specifically with its LED oriented to produce light toward an area to be illuminated. For example, when installed in a fixture in a ceiling that has a reflector as described above, the typical LED-based tube is installed to be oriented such that its LEDs face away from the reflector. Due to the orientation of the typical LED-based tube and the directional output of the typical LED-based tube when installed in the ceiling fixture, a large portion of produced light travels directly toward an area below the ceiling that is intended to be illuminated, and thus a typical LED-based tube produces minimal amounts of light in the direction toward the reflector. As a result, the reflectors attached to many fluorescent light fixtures serve little purpose when typical LED-based tubes are installed in the fixtures. 
       BRIEF SUMMARY 
       [0006]    While the typical LED-based light tube installed in a fluorescent fixture has its LEDs oriented in a common direction facing an area to be illuminated, the resulting light distribution towards the area to be illuminated may not be as uniform as the light distribution produced by a fluorescent tube. That is, the Lambertian distribution of light from the typical LED-based tube results in a bright area directly inline with the direction the LEDs face, while areas lateral of the bright area are typically illuminated to a lesser extent, if at all. 
         [0007]    Examples of LED-based light tubes with dual-sided light distributions as described herein can produce a more uniform distribution of light when installed in fluorescent fixtures having reflectors compared to known LED-based tubes. LED-based tubes with dual-sided light distributions can produce light in a first direction toward an area to be illuminated and can also produce light in a second direction different from the first direction. The second direction can be generally opposite the first direction. The amount of light produced toward the first direction can be, but need not necessarily be, greater than the amount of light produced toward the second direction. As a result, when installed in a fluorescent fixture that has a reflector, light produced toward the first direction can travel directly toward an area to be illuminated without being reflected or otherwise re-directed once exiting the LED-based tube. Light produced toward the second direction, however, can be reflected by the reflector and re-directed toward the area to be illuminated. The light produced toward the second direction can thus be spread out prior to reaching the area to be illuminated, thus increasing the uniformity of the distribution of light emanating from the tube. The combination of the light produced in the first direction traveling directly toward the area to be illuminated and the light produced in the second direction that is re-directed by the reflector can provide an improved distribution of light compared to known LED-based lights. 
         [0008]    One embodiment disclosed herein of an LED light for use in a fluorescent light fixture comprises a housing and a circuit board having a first surface configured to face an illumination area, the circuit board mounted in the housing and defining a plane conceptually dividing the housing into a first portion and a second portion. At least one LED is mounted on the first surface of the circuit board and is configured to emanate light in a first direction. Light distribution means is configured to distribute a portion of the light emanated in the first direction to at least a second direction different than the first direction. 
         [0009]    Another embodiment of an LED light for use in a fluorescent light fixture comprises a housing and a circuit board having a first surface configured to face an illumination area, the circuit board mounted in the housing and defining a plane conceptually dividing the housing into a first portion and a second portion. A plurality of LEDs is mounted on the first surface of the circuit board and is configured to emanate light in a first direction through the first portion of the housing. Apertures in the circuit board are configured to pass light reflected by the first portion of the housing in at least a second direction through the second portion of the housing. 
         [0010]    Yet another embodiment of an LED light for use in a fluorescent light fixture comprises a housing and a circuit board having a first surface configured to face an illumination area and an opposing second surface. A first plurality of LEDs is mounted on the first surface of the circuit board and configured to emanate light in a first direction through the first portion of the housing. A second plurality of LEDs is mounted on the second surface of the circuit board and configured to emanate light in a second direction through the second portion of the housing. 
         [0011]    Also disclosed herein are methods of distributing light in a plurality of directions from an LED-based light. One such method of distributing light in more than one direction from an LED light for use in a fluorescent light fixture comprises emanating light in a first direction from at least one LED positioned on a circuit board facing an illumination area, deflecting a portion of the light emanated in the first direction in a second direction with a portion of a housing, passing the portion of the light emanated in the second direction through apertures in the circuit board and reflecting light back toward the illumination area with the reflector. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0013]      FIG. 1  is a side view of a first example of an LED-based light tube with dual-sided light distribution; 
           [0014]      FIG. 2  is a bottom plan view of the LED-based light tube with dual-sided light distribution of  FIG. 1 ; 
           [0015]      FIG. 3  is a cross section view of the LED-based light tube of  FIG. 2  along line A-A; 
           [0016]      FIG. 4  is a top plan view of an example of a circuit board of another example of a LED-based light tube with dual-sided light distribution; 
           [0017]      FIG. 5  is a side view of another example of an LED-based light tube with dual-sided light distribution; 
           [0018]      FIG. 6  is a bottom plan view the example of the LED-based light tube with dual-sided light distribution of  FIG. 5 ; 
           [0019]      FIG. 7  is a top plan view of the LED-based light tube of  FIG. 5 ; 
           [0020]      FIG. 8  is a cross section view of the LED-based light tube of  FIG. 5  along line B-B; and 
           [0021]      FIG. 9  is a cross section view of yet another example of an LED-based light with dual-sided light distribution taken along a plane perpendicular to a longitudinal axis of the light. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIGS. 1-9  illustrate examples of LED-based lights having dual-sided distributions. In the example illustrated in  FIGS. 1-3 , an LED-based light tube  10  is configured as a replacement for a fluorescent tube in a fluorescent fixture. The light tube  10  includes a housing  12 , a circuit board  14  in the housing  12  that defines a plurality of apertures  16 , one or more LEDs  18  mounted on the circuit board  14 , and a pair of end caps  20  attached at opposing ends of the housing  12 . The light tube  10  can additionally include other components, such as electrical components or one or more highly thermally conductive structures for enhancing heat dissipation. 
         [0023]    The housing  12  as shown in  FIGS. 1-3  is a light transmitting cylindrical tube. The housing  12  can be made from polycarbonate, acrylic, glass or another light transmitting material. The housing  12  can be transparent or translucent. For example, a translucent housing  12  can be made from a composite, such as polycarbonate with particles of a light refracting material interspersed in the polycarbonate. While the illustrated housing  12  is cylindrical, the housing  12  can alternatively have a square, triangular, polygonal, or other cross sectional shape. Similarly, while the illustrated housing  12  is linear, the housing  12  can have an alternative shape, e.g., a U-shape or a circular shape. Additionally, the housing  12  need not be a single piece as shown in  FIGS. 1 and 2 . Instead, the housing  12  can be formed by connecting multiple individual parts, not all of which need be light transmitting. The housing  12  can have a length such that the light  10  is approximately 48″ long, and the housing  12  can have a 0.625″, 1.0″, or 1.5″ diameter for engagement with common fluorescent fixtures. The housing  12  can be manufactured to include light diffusing or refracting properties, such as by surface roughening or applying a diffusing film to the housing  12 . 
         [0024]    While the illustrated circuit board  14  is shown as an integral circuit board, multiple circuit board sections can be joined by bridge connectors to create the circuit board  14 . The circuit board  14  as shown in  FIGS. 1-3  can be slidably engaged with the housing  12 , though the circuit board  14  can alternatively be clipped, adhered, snap- or friction-fit, screwed or otherwise connected to the housing  12 . Also, other types of circuit boards may be used, such as a metal core circuit board. 
         [0025]    The end caps  20  can be attached at opposing longitudinal ends of the housing  12  for physically and electrically connecting the bulb  10  to a fixture. The end caps  20  can be the sole physical connection between the bulb  10  and fixture. The end caps  20  can be electrically connected to the circuit board  14  for providing power to the LEDs  18 . Each end cap  20  is illustrated with two pins  22 , though two of the total four pins can be “dummy pins” that do not provide an electrical connection. Alternatively, other types of electrical connectors can be used, such as an end cap carrying a single pin. Also, while the end caps  20  are shown as including cup-shaped bodies, the end caps  20  can have a different configuration, for example, the end caps  20  can be shaped to be press fit into the housing  12 . One or both of the end caps  20  can additionally include electric components, such as a rectifier and filter. 
         [0026]    The LEDs  18  can be surface-mount devices of a type available from Nichia, though other types of LEDs can alternatively be used. For example, although surface-mounted LEDs  18  are shown, one or more organic LEDs can be used in place of or in addition thereto. Each LED  18  can include a single diode or multiple diodes, such as a package of diodes producing light that appears to an ordinary observer as coming from a single source. The LEDs  18  can emit white light. However, LEDs that emit blue light, ultra-violet light or other wavelengths of light can be used in place of white light emitting LEDs  18 . The number of LEDs  18  can be a function of the desired power of the light tube  10  and the power of the LEDs  18 . For a 48″ light, such as the illustrated tube  10 , the number of LEDs  18  can vary from about five to four hundred such that the tube  10  outputs approximately 500 to 3,000 lumens. However, a different number of LEDs  18  can alternatively be used, and the light tube  10  can output another amount of lumens. The LEDs  18  can be evenly spaced along the circuit board  16 , and the spacing of the LEDs  18  can be determined based on, for example, the light distribution of each LED  18  and the number of LEDs  18 . 
         [0027]    The light tube  10  of  FIGS. 1-3  can be installed in a fluorescent fixture by engaging the end caps  20  with the fixture with the circuit board  14  and LEDs  18  oriented to face the area to be illuminated. When installed in a fluorescent fixture with a reflector and energized, the light tube  10  produces a first flux of light in a first direction  24  toward an area to be illuminated, for example, an area directly below the fixture and its surrounding area when the fixture is in a ceiling. Additionally, the light tube  10  produces a second flux of light in a second direction  25  generally opposite the first direction  24 . The first flux of light can be greater than the second flux of light, though it need not necessarily be (e.g., the two fluxes of light can be generally equal). The reflector, such as a mirror or a piece of plastic, ceiling or other material having a reflective coating, is typically on an opposing side of the light tube  10  from the area to be illuminated, such as above the light tube  10  when the fixture is on a ceiling. The reflector is represented as numeral  23  in  FIG. 3 . The reflector  23  is typically configured to reflect light in the first direction  24  toward the area to be illuminated. The second flux of light is produced by deflection of the housing  12  in a direction toward the reflector  23 . The reflector  23 , in turn, can redirect the second flux of light toward the area to be illuminated. That is, when installed in a fixture including a reflector  23 , the light tube  10  produces the first flux of light directly toward the area to be illuminated and produces the second flux of light indirectly toward the area to be illuminated via the reflector  23 . The reflector  23  can spread out the second flux of light such that the light tube  10  produces a similar distribution of light to a fluorescent tube when installed in the fixture. As a result, the LED-based light tube  10  can provide a more even distribution of light than an LED-based light tube that produces light in a single direction when installed in the fixture including the reflector  23 . 
         [0028]    Referring now to  FIG. 3 , a plane  27  defined by the circuit board  14  can conceptually divide the housing  12  into a first half  12   a  and a second half  12   b , and the first and second halves  12   a  and  12   b  can have different light diffusing and/or refracting properties (e.g., different amounts of surface roughening can be provided on the halves  12   a  and  12   b , or different types of diffusing film can be applied to the halves  12   a  and  12   b ). The first half  12   a  can be configured to diffuse and/or deflect light to a greater extent than the second half  12   b , and the amount of diffusion and/or deflection provided by the first half  12   a  can affect the amount of light produced in the first direction  24  compared to the second direction  25 . That is, increasing the diffusing and/or deflection properties of the first half  12   a  can cause a greater amount of light to be internally deflected by the first half  12   a , and light internally deflected by the first half  12   a  can be provided in the second direction  25 . Further, providing different light diffusing and/or deflecting properties on the first and second halves  12   a  and  12   b  of the housing  12  can allow for diffusing or otherwise spreading light traveling in the first direction  24  by a different amount than light traveling in the second direction  25 . For example, the first half  12   a  can diffract and/or diffuse light to a greater extent than the second half  12   b  to reduce the directional appearance of light traveling in the first direction  24 , which can exit the housing  12  traveling in the direction  24  directly toward the area to be illuminated and thus more easily visible from a point of view of an observer in the area to be illuminated. The second half  12   b  can diffuse and/or refract light to a lesser extent than the first half  12   a , as this can enhance the amount of light that exits through the second half  12   b  of the housing  12  without being internally reflected. 
         [0029]    Further, the light diffusing and/or deflecting properties of the housing  12  can vary about the circumference of the each tube half  12   a  and  12   b . For example, the tube half  12   a  can be configured to provide greater light diffusion or deflection over an area normal to the circuit board  14  and inline with the LEDs  18  compared to an area circumferentially spaced therefrom by, as an example, providing greater surface roughening over the portion of the half  12   a  normal to the circuit board and inline with the LEDs  18  compared to the circumferentially spaced area. 
         [0030]    As another example, one or more areas, such as deflecting areas  12   c  and  12   d  as shown in  FIG. 2 , can be treated differently from other portions of the housing  12  to direct light from the LEDs  18  toward apertures  16  in the circuit board  14 . The apertures  16  allow light reflected by the first half  12   a  of the housing  12  toward the circuit board  14  to pass the circuit board  14 . The areas  12   c  and  12   d  can be treated to increase their light diffusing and/or refracting properties compared to a remainder of the half  12   a  such that the areas  12   c  and  12   d  internally reflect a large portion of light. This can be accomplished by, as examples, increasing an amount of surface roughening on the areas  12   c  and  12   d  compared to the rest of the half  12   a , applying different diffusing film to areas  12   c  and  12   d  than a remainder of half  12   a , or attaching one or more reflectors to the housing  12  over at least portions of the areas  12   c  and  12   d . The size and location of areas  12   c  and  12   d  and their properties can be selected to control the amount of light produced by the LEDs  18  that is directed through the apertures  16  defined by the circuit board  14 , and thus in the second direction  25 . For example, covering areas  12   c  and  12   d  with reflectors can provide a greater flux of light in the second direction  25  compared to roughening the surfaces of areas  12   c  and  12   d . Additionally, the areas  12   c  and  12   d  need not necessarily have different properties from a remainder of the first half  12   a  of the housing  12 , nor need the first half  12   a  necessarily have different properties than the second half  12   b . Alternatively, instead of two areas  12   c  and  12   d  configured to internally reflect light, one or more than two such areas can be included on the first half  12   a  of the housing  12 , and the locations of such areas can vary from as shown in  FIG. 2 . For example, in another example, a light-reflecting area can be directly above and inline with the LEDs  18 . 
         [0031]    The circuit board  14  as illustrated in  FIGS. 1-3  is an elongate printed circuit board defining the apertures  16  that allow light reflected by the first half  12   a  of the housing  12  toward the circuit board  14  to pass the circuit board  14 . Such light can then exit the second half  12   b  of the housing in at least the second direction  25  toward the reflector  23 . The sizes of the apertures  16  can be selected to control a ratio of fluxes of light directed in the first and second directions  24  and  25 . For example, increasing the sizes of the apertures  16  can allow for more light to be directed toward the second direction  25 . Additionally, the placement of the apertures  16  can also be affect the amount of light directed in the first direction  24  compared to the second direction  25 . The exemplary circuit board  14  shown in  FIGS. 2 and 3  defines apertures  16  inboard from longitudinal edges  14   a  and  14   b  of the circuit board  14 , and the circuit board  14  includes transversely extending bridges  14   c  extending transversely between the apertures  16 , which can strengthen the circuit board  14  and reduce the amount of light that passes the circuit board  14  toward the second half  12   b . While the apertures  16  are shown as rectangular holes, the apertures  16  can alternatively be circular, oval, or some other shape. 
         [0032]    The apertures  16  can be located at different positions on the circuit board  14  than shown in  FIGS. 2 and 3 . For example,  FIG. 4  shows another example of a circuit board  14 ′ that can be placed in the housing  12  and engaged with end caps  20 . The circuit board  14 ′ can have apertures  16 ′ formed out of longitudinal edges  14   a ′ and  14   b ′ of the circuit board  14 ′. Bridges  14   c ′ extend transversely outward from the circuit board  14 ′ between the apertures  16 ′ for connection to the housing  12 . As another example that is not illustrated, one or more apertures  16  can be formed along a longitudinal center line of the circuit board  14  between the LEDs. As still another example that is not illustrated, the circuit board  14  can have a width less than an inner radius of the housing  12 , in which case the circuit board  14  can be secured in the housing  12  via attachment to the end caps  20 , and gaps between the circuit board  14  and housing  12  can act as apertures  16 . 
         [0033]    The LEDs  18  can be mounted to the circuit board  14  at longitudinally spaced apart locations along a central portion of the circuit board  14  between the longitudinally spaced rows of apertures  16  as shown in  FIG. 2 . In other examples, however, the LEDs  18  can be mounted at other locations. For example, if apertures  16  occupy a central, longitudinally extending area of the circuit board  14 , LEDs  18  can be mounted in two longitudinally extending rows on opposing sides of the apertures  16 . 
         [0034]    Instead of relying on internally reflected light to produce light in the second direction  25 , an LED-based light tube  30  shown in  FIG. 5  has another example of a circuit board  40  that includes LEDs  18  mounted on a first side  40   a  of the circuit board  40  and a second side  40   b  opposite the first side  40   a . The circuit board  40  can be installed in the housing  12  and engaged with end caps  20  similar to the circuit board  14 . A greater number of LEDs  18  can be included on the first side  40   a  of the circuit board  40 , shown in  FIG. 6 , than the number of LEDs included on the second side  40   b , shown in  FIG. 7 , to provide more light directly to an area to be illuminated than indirectly to the area to be illuminated. Alternatively, the same number of LEDs  18  can be included on each side  40   a ,  40   b . When installed in a fixture, the first side  40   a  can be oriented to face the first direction  24  toward the area to be illuminated and the second side  40   b  can face in the second direction  25  toward a reflector, as shown in  FIG. 5 . As such, light produced from the LEDs  18  on the second side  40   b  can be distributed by the reflector toward the area to be illuminated, allowing the light tube  30  in which the circuit board  40  is installed to provide an even distribution of light closely replicating a fluorescent tube.  FIG. 8  is a cross section of the LED-based light tube  30  along line B-B and illustrates the location of the reflector  23  of the light fixture. 
         [0035]    Another example of an LED light tube  100  capable of producing light in the first and second directions  24  and  25  is shown in cross section in  FIG. 9 . The tube  100  includes a circuit board  102  and a housing  104  as described with reference to the other figures. The circuit board  102  can define apertures  105  that allow light traveling in the first direction  24  and directed by the housing  104  toward the second direction  25  to pass the circuit board  102  in the second direction  25 , similar to apertures  16  as described above. The apertures  105  can be radially between the circuit board  102  and the housing  104 . For example, the circuit board  102  can have a width less than an interior diameter of the housing  104  and can be secured to end caps at opposing ends of the housing  104 . Alternatively, the circuit board  105  can have an alternative shape defining apertures, such as a shape similar to the circuit board  14 ′, in which case the apertures  105  can be between portions of the circuit board  105  similar to portions  14   c ′ of circuit board  14 ′, although the apertures  105  need not necessarily be radially outward of the circuit board  102 . 
         [0036]    The housing  104  can additionally include a light pipe portion  106 . The light pipe portion  106  can include light inlets  108  aligned with the apertures  105 . As a result, light produced by the LEDs  18  and directed by the housing  104  toward the apertures  105  can enter the light pipe  108 . The light pipe  106  can guide light around a circumference of the housing  104 , with light exiting the light pipe  106  at various circumferential locations. As a result, the light pipe  106  can allow light to exit the housing  104  and travel in the second direction  25 , thereby facilitating a generally even distribution of light in the second direction  25 . Light exiting the light pipe  106  can strike a reflector of a fixture in which the tube  100  is installed and can be reflected toward an area to be illuminated. 
         [0037]    The above-described examples have been described in order to allow easy understanding of the invention and do not limit the invention. On the contrary, the invention is intended to cover various modifications and equivalent arrangements, whose scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structure as is permitted under the law.