before describing in detail embodiments that are in accordance with the present invention , it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to a light emitting panel for medical applications . accordingly , the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings , showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein . in this document , relational terms such as first and second , top and bottom , and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions . the terms “ comprises ,” “ comprising ,” or any other variation thereof , are intended to cover a non - exclusive inclusion , such that a process , method , article , or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process , method , article , or apparatus . an element proceeded by “ comprises . . . a ” does not , without more constraints , preclude the existence of additional identical elements in the process , method , article , or apparatus that comprises the element . in this document , relational terms such as first and second , top and bottom , and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions . the terms “ comprises ,” “ comprising ,” or any other variation thereof , are intended to cover a non - exclusive inclusion , such that a process , method , article , or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process , method , article , or apparatus . an element proceeded by “ comprises . . . a ” does not , without more constraints , preclude the existence of additional identical elements in the process , method , article , or apparatus that comprises the element . in one preferred embodiment of the present invention as shown in fig1 , the light emitting panel 100 comprises four layers : a light emitting layer 101 , a holographic diffusion layer 102 , a reflection layer 103 , and a transparent cover layer 104 . the light emitting layer 101 comprises one or more side - emitting optical fibers 105 , which are coiled to form a panel - like structure . the side - emitting fiber 105 comprises a diffusive interface between its core and cladding region . the roughness of the diffusive interface is controlled so that a desired portion of the light in the core region is refracted to emit from the side surface of the fiber . a section of common end - emitting optical fiber 106 is employed to deliver the light from the led light source 107 to the proximal end 108 of the side - emitting fiber 105 . the distal end 109 of the side - emitting fiber 105 is reflection coated to prevent unwanted light leakage and further increase the light emitting efficiency of the side - emitting fiber 105 . the holographic diffusion layer 102 is used to homogenize the light beam emitted from the light emitting layer 101 . one example of such a holographic diffuser can be found in u . s . pat . no . 6 , 446 , 467 by lieberman et al ., which is hereby incorporated by reference . the holographic diffuser features an ultra - high transmittance of 85 - 90 % in comparison with conventional frost glass diffusers . the reflection layer 103 is placed under the light emitting layer 101 to convert the downward light emission into upward light emission . the light emitting panel is flexible in nature . thus it can be applied to any body parts of the patient with any complex contours . a more detailed illustration of the led - to - fiber coupling stage is shown in fig2 . the led 107 comprises an led chip 107 a surface - mounted on a thermal conductive substrate 107 b . this chip - on - board ( cob ) package provides better heat dissipation for the led chip 107 a . thus it allows a larger light emitting surface and a higher drive current for the led chip 107 a to increase its output power . it also leads to long lifetime as well as wavelength and intensity stability . an epoxy dome lens 107 c coated on the surface of the led chip 107 a is used to control its radiation pattern . the led 107 may further comprise a reflective cup ( not shown in the figure ) for better light collection efficiency . the whole led module is mounted on an aluminum heat sink 110 for improved heat dissipation . the light emitted from the led 107 is coupled into an end - emitting optical fiber 106 through a lens set 111 . the numerical aperture ( na ) and core diameter of the end - emitting optical fiber 106 are selected to match with the divergence angle and diameter of the led beam that emitted from the lens set 111 for effectively collecting the led light . the coupling lens set 111 comprises two pieces of single lens 111 a and 111 b , which are designed to have a large numerical aperture ( f / 1 . 0 ) and a small aberration to achieve high coupling efficiency . in this embodiment , a high led - to - fiber light coupling efficiency of greater than 40 percent (& gt ; 40 %) is achieved . the led 107 , the lens set 111 and the fiber 106 are assembled together using fixture 112 , 113 , 114 and 115 to improve the mechanical and thermal stability of the coupling stage . in the foregoing specification , specific embodiments of the present invention have been described . however , one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below . for example , with the advance of semiconductor technology , higher intensity leds will be readily available . thus the number of leds used in the photo - therapy apparatus can be further reduced . accordingly , the specification and figures are to be regarded in an illustrative rather than a restrictive sense , and all such modifications are intended to be included within the scope of present invention . the benefits , advantages , solutions to problems , and any element ( s ) that may cause any benefit , advantage , or solution to occur or become more pronounced are not to be construed as a critical , required , or essential features or elements of any or all the claims . the invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued .
a light emitting panel is disclosed for medical applications including photodynamic therapy and photo bio - stimulation . the light emitting panel utilizes high intensity light emitting diodes as its light source and side - emitting optical fibers for light delivery .