Abstract:
Disclosed herein are embodiments of replacement lights for conventional fluorescent tube lights for use in a conventional fluorescent fixture. One embodiment comprises a tubular housing, a circuit board disposed within the housing, a pair of end caps disposed on opposing ends of the tubular housing with at least one pin connector extending from each end cap, an array of LEDs arranged longitudinally along the circuit board, a number and spacing of the LEDs being such as to uniformly and fully occupy a space between the end caps, wherein at least one of the connectors is electrically connected to the LEDs and a wavelength-converting material in contact with at least a portion of the tubular housing. The wavelength-converting material is excited by transmitted light from the LEDs to produce visible light.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Applications with Ser. Nos. 61/219,625 filed on Jun. 23, 2009 and 61/317,798 filed on Mar. 26, 2010, both of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a light emitting diode (LED) based light for replacing a conventional fluorescent tube in a fluorescent light fixture having a wavelength conversion layer. 
       BACKGROUND 
       [0003]    Conventional fluorescent tubes are gradually being replaced by LED-based replacement lights in many applications. LED-based replacement lights have many advantages over conventional fluorescent tubes including, inter alia, longer operational life and reduced power consumption. 
         [0004]    A single LED in an LED-based replacement light can only produce a single color, such as red, green, blue, amber, or yellow. To produce white light, light from LEDs can be converted to light spanning the visible spectrum by using color mixing. Color mixing can involve utilizing multiple LEDs in a device and varying the intensity of each LED to produce white light. However, color mixing may entail packing additional LEDs into one source and can require additional optics to mix the light from the multiple LEDs, which can introduce extra losses and increase the cost of the replacement light. 
       BRIEF SUMMARY 
       [0005]    Disclosed herein are embodiments of replacement lights for conventional fluorescent tube lights for use in a conventional fluorescent fixture. One embodiment comprises a tubular housing, a circuit board disposed within the housing, a pair of end caps disposed on opposing ends of the tubular housing with at least one pin connector extending from each end cap, an array of LEDs arranged longitudinally along the circuit board, a number and spacing of the LEDs being such as to uniformly and fully occupy a space between the end caps, wherein at least one of the connectors is electrically connected to the LEDs and a wavelength-converting material in contact with at least a portion of the tubular housing. The wavelength-converting material is excited by transmitted light from the LEDs to produce visible light. 
         [0006]    Another embodiment disclosed herein of a replacement light for a conventional fluorescent tube light for use in a conventional fluorescent fixture comprises a tubular housing having a back portion and a front portion attached to the back portion, a circuit board disposed along the back portion of the tubular housing, a pair of end caps disposed on opposing ends of the tubular housing with at least one pin connector extending from each end cap, an array of LEDs arranged longitudinally along the circuit board opposite the back portion, a number and spacing of the LEDs being such as to uniformly and fully occupy a space between the end caps, wherein at least one of the connectors is electrically connected to the LEDs and a wavelength-converting layer in contact with at least a portion of the front portion of the tubular housing. The wavelength-converting material is excited by transmitted light from the LEDs to produce visible light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0008]      FIG. 1  is a perspective view of a LED-based replacement light in accordance with one embodiment of the invention and a fluorescent fixture; 
           [0009]      FIG. 2  is a cross-section view of the LED-based replacement light of  FIG. 1  at a position similar to line A-A; 
           [0010]      FIG. 3  is a cross-section view of another embodiment of the LED-based replacement light at a position similar to line A-A; 
           [0011]      FIG. 4  is a cross-section view of another LED-based replacement light in accordance with an embodiment of the invention along a line similar to line A-A in  FIG. 1 ; and 
           [0012]      FIG. 5  is a perspective view of a LED-based replacement light in accordance with another embodiment of the invention and a fluorescent fixture. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The embodiments disclosed herein can provide a separate wavelength-conversion layer remote from the LEDs themselves. This provides for operation of the wavelength-conversion coating or wavelength-converting material at a lower temperature and light intensity than would be possible if it were packaged with the LED chips. This separation allows a phosphor layer to also function as a diffusing material to obscure the bright points of light produced by the LEDs and spread the light from the tube, without introducing extra light losses that would be produced by using a single-purpose diffusing layer in addition to a phosphor contained in the LED package. 
         [0014]      FIGS. 1 and 2  illustrate an LED-based replacement light  10  according to the embodiments discloses herein for replacing a conventional fluorescent light tube in a fluorescent fixture  12 . The light  10  can include a circuit board  14 , multiple UV/blue LEDs  16  (hereafter LEDs), a tubular housing  18  at least partially defined by a high-dielectric translucent portion and coated by a wavelength-converting layer  20 , and bi-pin electrical connectors  22  affixed to plastic end caps  23 . 
         [0015]    The circuit board  14  can have a LED-mounting side  14   a  and a primary heat transferring side  14   b  opposite the LED-mounting side  14   a . The circuit board  14  may be made in one piece or in longitudinal sections joined by electrical bridge connectors. The circuit board  14  can be one on which metalized conductor patterns can be formed in a process called “printing” to provide electrical connections from the connectors  22  to the LEDs  16  and between the LEDs  16  themselves. An insulative board is typical, but alternatively, other circuit board types, e.g., metal core circuit boards, can be used. 
         [0016]    The LEDs  16  can be mounted at predetermined intervals  21  along the length of the circuit board  14  to uniformly emit light through a portion the tube  18 . LEDs  16  can emit electromagnetic radiation in the UV range, the blue range or in both the UV and blue ranges of the electromagnetic spectrum. 
         [0017]    The spacing  21  between LEDs  16  along the circuit board  14  can be a function of the length of the tube  18 , the amount of light desired, the wattage of the LEDs  16  or the viewing angle of the LEDs  16 . Thus, for example, if the light  10  is 48 inches long, the number of LEDs  16  may vary from about thirty to sixty such that the light  10  outputs approximately 3,000 lumens, and the spacing  21  between the LEDs  16  varies accordingly. The arrangement of LEDs  16  on the circuit board  14  is such as to substantially fill the entire space between the end caps  23 . 
         [0018]    End caps  23  carrying bi-pin connectors  22  are attached to each longitudinal end of the tube  18  for physical and electrical connection of the light  10  to the fixture  12 . Since the LEDs  16  in the present embodiment are directionally oriented, the light  10  should be installed at a proper orientation relative to a space to be illuminated to achieve a desired illumination effect. While the end caps  22  are shown as cup-shaped structures that slide over longitudinal ends of the tube  18 , alternative end caps that fit into the tube  18  can be used in place of the illustrated cup-shaped end caps  22 . Also, two of the pins  22  may be “dummy pins” for physical but not electrical connection to the fixture  12  thereby permitting only the other two pins  22  to be active. Bi-pin connectors  22  are compatible with many fluorescent fixtures  12 , though end caps  23  with alternative electrical connectors, e.g., single pin end caps, can be used in place of end caps  22  carrying bi-pin connectors  23  when desired. 
         [0019]    Still referring to  FIGS. 1 and 2 , the tube  18  can include a longitudinally extending flat interior surface  24  for supporting the circuit board  14 . The surfaces  26   a  and  26   b  of the tube  18  on either side of the circuit board  14  are optionally contoured to the sides of the circuit board  14 . The exterior of the tube  18  can optionally be D-shaped, with the exterior flat portion corresponding to the location of the flat interior surface  24 . The tube  18  can be formed of polycarbonate, acrylic, glass, or another high-dielectric light transmitting material. As used herein, the term “high-dielectric” means a material which has a low conductivity to direct current; e.g., an insulator. 
         [0020]    The tube  18  can include optional tabs  28  for securing the circuit board  14 . The tabs  28  can project from the tube  18  on opposite sides of the circuit board  14  and contact the LED-mounting side  14   a  of the circuit board  14 . The tabs  28  can be formed integrally with the tube  18  by, for example, extruding the tube  18  to include the tabs  28 . Each tab  28  can extend the entire length of the tube  18 , though a series of discrete tabs  28  can alternatively be used to secure the circuit board  14 . 
         [0021]    The wavelength-converting layer  20  can be placed on an inner surface  18   a  of the tube  18 . The wavelength-converting layer  20  can be placed on the entire inner surface  18   a  of the tube  18 , or the wavelength-converting layer  20  can be placed along a portion of the inner surface  18   a  of the tube  18  through which a majority of light passes. The wavelength-converting layer  20  can be composed of a transparent resin containing one or more phosphors such as a mono-, bi-, tri-phosphor blend or any other blend as desired or required. If multiple phosphors are used, distinct colors such as yellow, green, red and the like can be applied to several layers of wavelength-converting layer  20 . The phosphor may emit a white or yellow light or if multiple phosphors are used, the phosphor may emit different colors which can be combined to produce a resulting white or yellow light. Alternatively, as shown in  FIG. 3 , instead of forming a separate layer, the wavelength-converting material could be incorporated into part or all of the material of the tube  18 ′, for example by molding, extrusion or co-extrusion. 
         [0022]    The color and number of the single or multiple phosphors may be dependent on the type of LEDs  16 . Thus, for example, a light  10  may contain blue LEDs, such as InGAN blue LEDs, and a wavelength-converting material containing yellow phosphor, such as YAG:Ce. Blue light emitted from the blue LED is used to excite the yellow phosphor, producing approximately white light. Alternatively, a white LED, formed using a blue LED chip and a phosphor emitting a high color temperature white light, could be used as the light source, and a quantum dot wavelength conversion material used as the active material in the wavelength-converting layer  20  to convert the light to a lower color temperature. 
         [0023]    Other combinations of different LEDs and different wavelength-converting layers  20  are available as desired or as required. 
         [0024]    In the above-described light  10 , when emission takes place from the LEDs  16  and light is emitted, the light is directed to the wavelength-converting layer  20 . The blue, UV or blue and UV light then collides with the wavelength-converting layer  20  and excites the phosphor contained therein. 
         [0025]    Wavelength-converting layer  20  can also act as a free diffuser. Wavelength-converting layer  20  can include, for example, a distribution of transparent particles or air bubbles. The transparent particles or air bubbles can repeatedly refract or diffuse the light emitted from LEDs  16 , which can aid in more uniformly distributing the light from the LEDs. Further, wavelength-converting layer  20  may have a high coefficient of thermal conductivity. As a result, the wavelength-converting material can act as a heat sink by dissipating heat produced by the LEDs  16 . 
         [0026]      FIG. 3  illustrates the tube  18  containing light diffracting structures, such as longitudinally extending ridges  25  formed on the interior of the tube  18 . Longitudinally extending ridges  25  assist in uniformly distributing light to the environment to be illuminated in order to replicate the uniform light distribution of conventional fluorescent bulbs the light  10  is intended to replace. Alternatively, light diffracting structures can include dots, bumps, dimples, and other uneven surfaces formed on the interior or exterior of the tube  18 . The light diffracting structures can be formed integrally with the tube  18 , for example, by molding or extruding, or the structures can be formed in a separate manufacturing step such as surface roughening. The light diffracting structures can be placed around an entire circumference of the tube  18 , or the structures can be placed along an arc of the tube  18  through which a majority of light passes. In addition or alternative to the light diffracting structures, a light diffracting film can be applied to the exterior of the tube  18  or placed in the tube  18 , or the material from which the tube  18  is formed can include light diffusing particles. 
         [0027]    The wavelength-converting layer  20  can be placed on the longitudinally extending ridges  25  or alternatively, can be placed on the entire inner surface  18   a  of the tube  18 . When light is emitted from the LEDs  16 , the light is directed to the wavelength-converting layer  20 . The blue, UV or blue and UV light then collides with the wavelength-converting layer  20  and excites the phosphor contained therein. The white or yellow light emitted from the phosphor can pass through longitudinally extending ridges  25 , which in turn, provides a more even distribution of light to the environment to be illuminated. 
         [0028]      FIG. 4  illustrates an LED-based replacement light  100  according to another embodiment of the present invention for replacing a conventional fluorescent light tube in the fluorescent fixture  12 . Features in this embodiment, which are similar to features already discussed with reference to the embodiment of  FIGS. 1-2 , are referenced using the same numerals and are not discussed in further detail. Unlike the embodiment illustrated in  FIGS. 1-2 , this embodiment contains a housing  118  with a back portion  140  with a semicircular cross-section that holds the circuit board  14  on which the LEDS  16  are mounted and electrically interconnected. A transparent or translucent front portion  142  with a semicircular cross-section, attaches to the back portion  140  to enclose circuit board  14  and LEDs  16  and circuit board. 
         [0029]    In this embodiment, the back portion  120  can be made of a metal such as aluminum to assist in heat dissipation from the LEDs  16 . In other embodiments, the back portion  120  can be made of any other suitable material. For example, back portion  120  can be made of steel. Further, embodiments of the present invention are not limited to a back portion that is semicircular in cross-section. For example, in other embodiments, the back portion can be of a rectangular or triangular cross-section or any other suitable cross-section. 
         [0030]    Front portion  142  can made of high-dielectric material such as an acrylic plastic. In other embodiments, the front portion  142  can be made of any other suitable material. For example, the front portion  142  can be made of glass. Embodiments of the present invention are not limited to a front portion that is semicircular in cross-section. For example, in other embodiments, the front portion can be of a rectangular or triangular cross-section or any other suitable cross-section. 
         [0031]    Like the embodiment of  FIGS. 1 and 2 , front portion  142  is coated by wavelength-converting layer  20 . The wavelength-converting layer  20  can be placed on an inner surface of the front portion  142 . The wavelength-converting layer  20  can be placed on the entire inner surface  18   a  of the tube  18 , or the wavelength-converting layer  20  can be placed along a portion of the inner surface  18   a  of the tube  18  through which a majority of light passes. 
         [0032]    The above-described embodiments 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 included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structure as is permitted under the law.