Abstract:
A light emitting diode (LED) array with beam directors outputting a high-intensity collimated beam. The LED array is constructed from a substrate component on which the LEDs and necessary electronics are disposed and a director attachment having a plurality of beam directors. The beam directors have a unique structure that is designed to shape the light beam into a collimated form. The LEDs are arranged in a pattern on the substrate, and the beam directors are arranged within the director attachment to coincide with the LEDs. The substrate and the director attachment may be manufactured and processed as separate components; they are then affixed together for operation.

Description:
[0001]     This application claims priority to U.S. provisional application Ser. No. 60/782,744 filed on Mar. 15, 2006. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to light emitting diodes (LEDs) and, more particularly, to LED arrays. The present invention provides a new LED array that utilizes a new beam director structure to output a beam of light.  
         [0004]     2. Description of the Related Art  
         [0005]     LEDs are semiconductor photon sources that can serve as highly efficient electronic-to-photonic transducers. They are typically forward-biased p-n junctions fabricated from a semiconductor material that emit light via injection electroluminescence. Their small size, high efficiency, high reliability, and compatibility with electronic systems make them very useful for a multitude of applications. Recent advancements have yielded high-power LEDs in a range of colors. This new generation of LEDs is useful in applications requiring a higher intensity light output such as high-power flash lights, airplane lighting systems, fiber-optic communication systems, and optical data storage systems.  
         [0006]     LEDs are generally divided into classes depending on their power rating. Although there is no standard range for the different classes, low-power LEDs typically have a power rating not greater than 0.2 watts, and high-power LEDs typically have a rating of at least 1.0 watts.  
         [0007]     Conventional packaging for low-power LEDs typically includes a reflector cup with the LED mounted at the bottom of the cup. Cathode and anode leads are electrically coupled to the LED to provide electrical power. The cathode lead can extend through the reflector cup and the anode lead can be wire bonded, or vice versa. The main function of the reflector cup is to redirect light emitted in certain directions in order to control the far-field intensity pattern of the LED.  
         [0008]     For applications requiring a high-intensity output, LEDs are often arranged in arrays and powered with a common source. If reflector cups are used, then they must also be arranged in a matching array. It can be technically challenging and costly to create a uniform array of reflector cups. Furthermore, because various applications require a beam having specific characteristics, it can be costly to manufacture several different LED/reflector cup arrays to test and produce the required beam.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides a light emitting diode (LED) array that produces a beam of light.  
         [0010]     One embodiment of an LED array according to the present invention comprises a substrate; a plurality of LEDs arranged in a pattern on the substrate; an electronics component disposed on the substrate, powering said plurality of LEDs; and a director attachment affixed to the substrate, the attachment having a pattern of beam directors arranged to correspond with the LEDs.  
         [0011]     Another embodiment of a beam forming apparatus according to the present invention comprises a power source; an array of LEDs; an electronics component driving a plurality of LEDs; a director attachment with a plurality of portions removed from said attachment such that said removed portions define a plurality of beam directors; and a housing that protects and partially surrounds said array of LEDs, said electronics component and said director attachment.  
         [0012]     A method for fabricating an LED array is disclosed that comprises mounting a plurality of LEDs onto a substrate in a pattern; forming a director attachment to define a plurality of beam directors arranged in a pattern; aligning the director attachment with the substrate such that the beam directors coincide with the LEDs; and affixing the director attachment to the substrate.  
         [0013]     These and other further features and advantages of the invention would be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which: 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a top plan view of one embodiment of an LED array according to the present invention;  
         [0015]      FIG. 2  is a cross sectional view of the LED array along section line  2 - 2 ;  
         [0016]      FIG. 3  is a top plan view of a substrate and an electronics component according to the present invention;  
         [0017]      FIG. 4  is a cross sectional view of a beam director according to the present invention;  
         [0018]      FIG. 5  is a side view of a beam director with a computer-modeled ray trace shown;  
         [0019]      FIG. 6  is a cross sectional view of a portion of an LED array according to the present invention;  
         [0020]      FIG. 7  is a perspective view of a high intensity lighting apparatus according to the present invention;  
         [0021]      FIG. 8  is a graph showing the relative output as a function of the beam angle, describing an embodiment of the present invention; and  
         [0022]      FIG. 9  is a flow chart of a method for fabricating an LED array. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     The present invention provides an LED array that is capable of outputting a beam of light. The LED array according to the present invention includes a separately formed director attachment that can be affixed to a substrate on which the LEDs are disposed. Forming the director attachment separately allows for changes to be made to the design of the individual beam directors at a later stage in the manufacturing process. Also, different director attachments having differently shaped beam directors are interchangeable with the substrate and the LEDs. The shape of the beam directors affects the characteristics of the output beam and thus can be varied to meet specific design needs.  
         [0024]      FIG. 1  shows one embodiment of an LED array  100  according to the present invention. Director attachment  102  is shown affixed to substrate  104 . A portion of substrate  104  is shown protruding from under director attachment  102 . Two leads  106  are disposed on substrate  104  and can be attached to a power source (not shown in  FIG. 1 ) to drive LEDs  108 . LEDs  108  are disposed on substrate  104  in a pattern. The pattern can easily be changed to achieve a different LED arrangement. Substrate  104  can be made from a material having high thermal conductivity such that heat is drawn away from the LEDs  108  and spread throughout the material.  
         [0025]     Portions of director attachment  102  are removed (for example, cut away or ablated) to define a plurality of beam directors  110 . Beam directors  110  are arranged in a pattern designed to coincide with LEDs  108 . Director attachment  102  is aligned with substrate  104  prior to affixing the two pieces together. The alignment can be done by lining up the first set of guide bores  112  on director attachment  102  with the second set of guide bores  302  (shown in  FIG. 3 ) on substrate  104 . Guide pins  114  passing through both sets of guide bores may be used to facilitate the alignment process. When director attachment  102  and substrate  104  are aligned, LEDs  108  are positioned in the centers of beam directors  110  with beam directors  110  defining the only path for light emitted by LEDs  108  to escape.  
         [0026]      FIG. 2  is a cross sectional view of LED array  100  along section line  2 - 2 . Substrate  104  is shown affixed to the bottom side of director attachment  102 . LEDs  108  mounted on substrate  104  are disposed in the centers of beam directors  110 .  
         [0027]      FIG. 3  shows the electronics component of the LED array disposed on substrate  104 . Leads  106  electrically connect a plurality of traces  304  to power source  306 . LEDs  108  are disposed along traces  304 . LEDs  108  can be arranged in series or in parallel or in a combination thereof as shown in  FIG. 3  so long as voltage is sufficient at each LED  108  for light emission. A second set of guide bores  302  is disposed in the corners of the substrate  104 . As mentioned above, this second set of guide bores  302  can be used to align substrate  104  with director attachment  102  so that LEDs  108  are properly centered within beam directors  110 .  
         [0028]      FIG. 4  is a cross sectional view of an individual beam director  400 . Beam director  400  is formed by precisely machining a portion of the director attachment  102  away such that cavity  402  is formed. The remaining inner walls of director attachment  102  form beam director  400 . In the preferred embodiment, a radial cross section of the beam director  400  is defined by three segments. First segment  404  forms a junction with second segment  406  defined by cup angle  410 . Second segment  406  forms a junction with third segment  408  defined by flare angle  412 . Third segment  408  extends to the bottom edge of director attachment  102  forming base angle  414  with a line parallel to the bottom edge of director attachment  102 . Segments  404 ,  406  and  408  may be straight or curvilinear with the preferred embodiment having slightly curvilinear segments. Angles  410 ,  412  and  414  can be varied to achieve a different beam director shape, thus changing the characteristics of the output beam. The beam directors may be coated with a material designed to maximize reflection at a particular wavelength or range of wavelengths, for example, gold or silver.  
         [0029]     Beam directors may be arranged in various patterns to accommodate different array designs. The number of beam directors in a director attachment may also vary according to design. The preferred embodiment includes  60  beam directors arranged in the pattern illustrated in  FIG. 1 .  
         [0030]      FIG. 5  shows a computer ray trace model of light interacting with one embodiment of individual beam director  400  (shown in detail in  FIG. 4 ). Light rays  502  are traced from a light source  504  (modeled here as a point source) to the outside environment. Light rays  502  emanate omnidirectionally from light source  504 . Some of light rays  502  escape the cavity of the beam director without being redirected. Some others of light rays  502  are redirected by one of the surfaces of beam director  400  and output in a direction away from the substrate (not shown here) beneath the light source. Still some others of light rays  502  are redirected by a surface of beam director  400  and travel in a direction toward the substrate. All of light rays  502  together form a beam which can be collimated. The shape of the beam is determined by the shape of beam director  400 .  
         [0031]      FIG. 5  is only meant to illustrate a computer-generated example of how light interacts with one embodiment of beam director  400 . Accordingly,  FIG. 5  is not meant to limit the structure or function of any elements shown therein.  
         [0032]      FIG. 6  shows a cross sectional view of a portion of LED array  100 . Director attachment  102  is shown affixed to substrate  104  with LEDs  108  mounted to substrate  104  and centered at the base of beam directors  400 . Although director attachment  102  may be affixed to substrate  104  using various methods, the preferred embodiment as shown in  FIG. 6  employs a layer of epoxy  600  sandwiched between director attachment  102  and substrate  104 .  
         [0033]      FIG. 7  shows a perspective view of a beam forming apparatus  700 . LED array  702  is disposed inside housing  704 . Housing  704  protects LED array  702  and power source (not shown) from outside elements. Housing  704  may take nearly any shape and can be made from many materials as necessitated by the application. Beam forming apparatus  700  can output a high-intensity collimated beam  706 .  
         [0034]      FIG. 8  shows a graph illustrating the characteristics of a typical beam produced by the invention as disclosed. For purposes of this description, a collimated beam is defined as having a beam angle of 50 degrees or less. The graph shows the relative output as a function of the beam angle (in degrees). The beam angle is a well known parameter in the field and is generally specified as the off-axis angle where the output power drops to 50% of the peak value.  FIG. 8  shows a beam with a relative output of 0.5 (50%) at approximately −20 degrees and +20 degrees. Thus, the graph indicates a full width half maximum (FWHM), or beam angle, of 40 degrees. The preferred embodiment of the invention outputs a collimated beam with a beam angle of approximately 40 degrees.  
         [0035]      FIG. 9  is a flowchart illustrating a process for fabricating an LED array. The process comprises mounting a plurality of LEDs onto a substrate in a pattern as shown in  900  and forming a director attachment to define a plurality of beam directors arranged in a pattern as shown in  902 . Then the director attachment and the substrate are aligned such that the beam directors coincide with the LEDs as shown in  904 . The director attachment is then affixed to the substrate as shown in  906 . The flowchart in  FIG. 9  is not meant to limit the process to any particular order for performing the steps. For example, it is not important that the LEDs be mounted to the substrate prior to machining the director attachment.  
         [0036]     Although the present invention has been described in considerable detail with reference to certain preferred configurations thereof, numerous other variations and alternate embodiments will occur to those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only in terms of the appended claims.