From: chris@work.org   
      
   Am 22.10.2011 22:13, schrieb Mikko OH2HVJ:   
   > Salmon Egg  writes:   
   >   
   >> In article, Mikko OH2HVJ   
   >>> So, the question is: how would you explain the idea of optical invariant   
   >>> as simply as possible ?   
   >   
   >> I presume that by "optical invariant" you mean either conservation of   
   >> energy or, more subtly, brightness. Try again. Good luck.   
   >   
   >   
   > Correct.. I'm trying to get my customer understand that with the   
   > current limitations (total of 15mm^2 LED surface radiating into   
   > almost half-space and a 0.8mm NA 0.5 fiber) it is impossible   
   > to get more light into the fiber. Also, I'd like to be able to   
   > explain the same to our EEs.   
   >   
      
   Hi Mikko,   
   this optical invariant is something like conservation of brightness.   
   For engineers start explaining optical magnification:   
   If you magnify the object-size you de-magify the view angles.   
      
   If you have a small light source with large angle you can change it to large   
   with small angle (Laser beam).   
   If you have large beam with small angle (laser) you can change it to small   
   area with large angle - focusing.   
      
   But if you start with large area and large angle you can not gain anything.   
   When creating light in LEDs it is always with half space angles. Fibers have   
   less then half space. You need to  decrease   
   angles; but then you increase size.   
   The only solution is to look for LEDs with small emitters. The smallest one   
   will be a laser diode.   
      
   BTW there are 440nm 1W laser diodes for less than 100$ available. You could   
   couple hundreds of them into one of that   
   huge fiber. :-)   
      
   Does that help?   
      
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