>    
   JB   
      
   > > OK - Here's the physics question about these signs. The magic thing   
   >    
   > > about them is the letters "glow," you get net light output from the   
   >    
   > > disturbance on the surface. How is that happening? And here is a   
   >    
   > > thought experiment: If you were to mark on the surface of the sign   
   >    
   > > with a transparent marker, like a piece of parraffin, would it glow?   
   >    
   > > 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?   
   >    
   > > Finally, it seems that roughing the surface also makes it glow. This   
   >    
   > > probably trivial scattering untelated to "evanescent."   
   >    
   >    
   Phil:   
   >    
   > The guided light refracts normally into the binder of the marker ink,    
   >    
   > then scatters off the particles and other irregularities.   
   >    
      
   So, returning to the "operational definitions" above, we can make a prediction   
   based on your statement:   
   If I just put dye on the surface of a "light pipe" it will NOT glow like the   
   restaurant signs do. (I have not tried this, but want to.)   
      
   In the former, the dye could be just a dye solution painted on.    
      
   Would this be a reasonable test?   
      
   (You may think I have reservations about your theory - My reservations are   
   based on the odd behavior of absorbers - Although the dye layer will be too   
   thin to refract or scatter light, it can resonate in tune with the E field.   
   This may influence the    
   critical angle by adding a term to the complex index of refraction, causing   
   light to spill out. Another more esoteric theory might have it that the E   
   field is exciting the dye to glow. All this is a priori speculation to the   
   experiment.)   
      
   So that's it. JB   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)