And more: If you were to mark with a white-board marker which leaves little   
   or no bulk material, just some dye, would it also glow?    
   >    
   > JB   
   >    
   >    
   >    
   > 1. The signs are lit from the edge (out of sight), and can be considered a   
   planar "light pipe." There is a black background to enhance the effect.   
   =================   
      
   @@@ And, I will answer myself about marking with a whiteboard (or Sharpie   
   type) marker on a glass light pipe - Yes it will glow. But here's the next   
   question about that: Why does it emit light? There is a complex analysis that   
   the absorber dye has an    
   imaginary component in the refractive index, but the mystery to me is: why do   
   you get net light output from it?     
   jb   
      
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