Abstract:
An illumination system is provided, comprising: two lamps ( 10 ) generating white light; an integrator rod ( 30 ) having an axis ( 31 ) disposed between the two lamps ( 10 ) for receiving the white light from the two lamps ( 10 ) at an input end ( 32 ) and directing the white light out of an output end ( 34 ) opposite the input end ( 32 ); and two mirrors ( 20 ) proximate the input end ( 32 ) of the integrator rod ( 30 ) and angled toward the respective lamps ( 10 ) to reflect the white light from the two lamps ( 10 ) into the input end of the integrator rod ( 30 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U. S. Provisional Patent Application Ser. No. 60/574,498, entitled “Optimized Two Lamp Illumination System” and filed May 26, 2004, which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to an illumination system utilizing two lamps to achieve effective brightness and extend lamp life.  
       BACKGROUND OF THE INVENTION  
       [0003]     In typical illumination systems, there is a trade-off between lamp brightness and lamp life. In order to achieve effective brightness, a higher wattage lamp is typically used at the expense of lamp life. Thus, devices using illumination systems with higher wattage lamps have short lives, requiring expensive lamp replacement.  
       SUMMARY OF THE INVENTION  
       [0004]     The invention provides an illumination system utilizing two lamps to achieve effective brightness and extended lamp life. The illumination system comprises: two lamps generating white light; an integrator rod having an axis disposed between the two lamps for receiving the white light from the two lamps at an input end and directing the white light out of an output end opposite the input end; and two mirrors proximate the input end of the integrator rod and angled toward the respective lamps to reflect the white light from the two lamps into the input end of the integrator rod.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The invention will now be described with reference to accompanying figures of which:  
         [0006]      FIG. 1  shows an illumination system using two low wattage lamps according to an exemplary embodiment of the present invention;  
         [0007]      FIG. 2  shows the illumination system of  FIG. 1  with light paths from the two lamps;  
         [0008]      FIG. 3  shows a graph of the light flux, as a percentage of flux from a single high wattage lamp, for two exemplary illumination systems using two low wattage lamps according to an exemplary embodiment of the present invention; and  
         [0009]      FIG. 4  shows a geometric representation of an illumination system using two low wattage lamps according to an exemplary embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]     The present invention provides an illumination system utilizing two lamps to achieve effective brightness and extended lamp life. As shown in  FIG. 1 , the illumination system comprises two lamps  10 , two angled mirrors  20 , and an integrator rod  30 . In an exemplary embodiment of the invention the two lamps each comprise a low wattage arc lamp such an ultra high performance (UHP) lamp, generating white light  19  and having a wattage of between about 100 and 120 Watts, available from Philips of Eindhoven, The Netherlands. Lamps of this wattage will have a significantly greater life than lamps typically used in a single lamp illumination system, having a wattage of about 180 to 200 Watts. The lamps  10  include reflectors  12  to focus and direct the light. Light is created by forming an electrical arc between two electrodes  14 . The distance between these electrodes is referred to as the arc length, and is typically one of several standard arc lengths.  
         [0011]     The integrator rod  30  is disposed between the two lamps  10 , such that an axis  31  of the integrator rod  30  is at an essentially equal distance from each of the two lamps  10 , and the integrator rod  30  is offset from the lamps  10  along the axis  31 . The integrator rod has an essentially transparent input end  32  that is essentially perpendicular to the axis  31  and positioned toward the lamps  10 . An essentially transparent output end  34  is essentially perpendicular to the axis  31  and positioned away from the lamps  10 . While the integrator as shown in  FIG. 1  has a square cross-section, a cylindrical integrator is also contemplated within the scope of the invention.  
         [0012]     Two mirrors  20  are disposed approximately between the lamps  10 , slightly offset along the axis  31  of the integrator rod  30 . The mirrors  20  each have an essentially flat, rectangular reflective surface extending from a bottom edge  21  to a top edge  22 . The bottom edges  21  are disposed proximate the input end  32  of the integrator rod  30 . In an exemplary embodiment of the invention, the bottom edges  21  of the mirrors  20  meet at the axis  31  of the integrator rod  30 . The mirrors are angled with respect to the axis  31  of the integrator  30  to optimize the reflection of white light  19  from the respective lamps  10  into the input end  32  of the integrator rod  30 , as will be described in greater detail below.  
         [0013]     As shown in  FIG. 2 , the white light  11  from the lamps  10  is directed onto the respective mirrors  20 , at positions  26  (shown in  FIG. 3 ) proximate to the bottom edges  21  thereof. Reflected light  29  from each of the mirrors  20  enters the integrator rod  30  at the input end  32 , and an integrated light beam  39  exits the output end  34  of the integrator rod  30  essentially along axis  31 .  
         [0014]     The inventors have determined that the flux of the integrated light beam  39  varies with the arc length of the lamps and with the angle of the mirrors  20  to axis  31  of the integrator rod  30 , referred to as the mirror half angle because it is half of the included angle between the two mirrors  20 .  FIG. 3  shows calculated curves  41 ,  42  for light flux of integrated light beam  39  as a percentage of the light flux for a single lamp over a range of mirror half angles for lamps having an arc length of 1.0 mm and 1.3 mm, respectively. It should be noted that the peak flux occurs at a different half angle for the different arc lengths.  
         [0015]      FIG. 4  shows a geometric representation of the illumination system of the invention. Theta  25  is the angle between the axis  31  of the integrator rod (not shown in  FIG. 3 ) and one of the mirrors  20 . The vector B represents the white light  11  generated by one of the lamps  10 , having a length equal to the focal length of the lamps  10 , at an angle Beta  27  from a horizontal axis perpendicular to the axis  31  of the integrator rod  30 . The angle Beta  27  is 45 degrees. Therefore components Bx and By of the vector perpendicular and parallel, respectively to the axis  31  are each equal to the magnitude of vector B divided by √2.  
         [0016]     A number of conflicting geometrical factors affect the optimum angle for the mirrors  20  and the optimum position for the lamps  10  with respect to the mirrors  20  and the integrator rod  30 . Among these factors are: finite beam size, rays being blocked by the outside of the integrator rod, and rays reflected off of the mirrors that miss the input end of the integrator. The inventors have determined the angle for the mirrors  20  and position for the lamps  10  using a system analysis program. The calculated optimum values for the angle of the mirrors  20  with respect to the axis  31  of the integrator rod  30  for two exemplary arc lengths are provided in Table A as Theta. The optimum positions for the lamps are provided as Delta X and Delta Y, where Delta X is the calculated distance of the optimum position in a direction perpendicular to (and away from) the axis  31  of the integrator rod  30  from the origin of vector B having a magnitude equal to the focal length of the lamps  10  at an angle of 45 degrees from the axis  31  of the integrator rod  30 . Similarly, Delta Y is the calculated distance of the optimum position in a direction parallel to the axis  31  of the integrator rod  30  from the origin of vector B (and away from the integrator rod  30 ).  
                                   TABLE A                                   lamp arc length   Theta   Delta X   Delta Y                           1.0 mm   41 degrees   −13.85 mm   +0.315 mm            1.3 mm   42 degrees   −12.95 mm   +1.05 mm                      
 
         [0017]     The calculated light flux for the illumination systems having a 1.0 mm and 1.3 mm arc length and the mirror angles and positioning of table A are 144.34% and 126.88%, respectively of a single lamp illumination system using the same lamp.  
         [0018]     The foregoing illustrates some of the possibilities for practicing the invention. Many other embodiments are possible within the scope and spirit of the invention. It is, therefore, intended that the foregoing description be regarded as illustrative rather than limiting, and that the scope of the invention is given by the appended claims together with their full range of equivalents.