From: mscir@yahoo.com   
      
   On 10/22/2011 1:01 PM, Mikko OH2HVJ wrote:   
   > "anorton"  writes:   
   >   
   >> A related quantity is etendue. The overly simple definition is that it   
   >> is the product of the area of a light beam and the solid angle   
   >> diverging from it. As you trace rays that are not vignetted through   
   >> the optical system, the etendue can not decrease. If you find that it   
   >> is, then you are vignetting rays somewhere. Conservation of etendue   
   >> basically says you can not squeeze light energy into a smaller   
   >> "volume" in area*angle space.    The conservation is law can be proven   
   >> by conservation of energy.   Etendue can increase due to scattering   
   >> for, example, but if it does, then it means your downstream optical   
   >> system needs to handle more etendue (e.g. larger aperture, smaller   
   >> f/#) if you do not want to lose light.   
   >   
   > Actually conservation of etendue what I was thinking of; how to explain in   
   simple terms   
   > that light from multiple large-area LEDs cannot be focused through a   
   > small-diameter fiber. I remember having read the proof by conservation of   
   > energy, I just can't get it into my head anymore or find it from anywhere!   
   > I think that one was quite simple and should be understandable for my   
   > client!   
      
   What if you focused the light from each of the LEDs with a parabola, and   
   the focal point of each parabola was at the end of the fiber. Or am I   
   missing the point?   
      
   Mike   
      
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