XPost: alt.usage.english, sci.physics   
   From: dhatunen@cox.net   
      
   On Tue, 09 Aug 2011 18:13:40 +0100, Jonathan de Boyne Pollard wrote:   
      
   >> Our TV sets can show only three colours, [...]   
   >   
   > Apart from the ones with the latest gimmick: yellow.   
   >   
   >> A hypothetical Martian with four kinds of colour receptors [...]   
   >   
   > Of course, one doesn't have to go to Mars to find a creature whose   
   > visual apparatus differs from that of a human.  The humble honey bee can   
   > see into the ultra-violet, having receptor cells for ultra-violet, blue,   
   > and green.  Some butterflies and wasps have a four-colour receptor   
   > system: ultra-violet, blue, green, and red.   
   >   
   > Moreover the differences are not just in the types of receptors, but   
   > also in how they are wired up.  Some insects, including honey bees, have   
   > been shown to only respond to motion via the green receptors, for   
   > example.   
      
   Ultraviolet light is light of shorter wavelength (higher photon energy)   
   than visible light, but the boundary between the two is not specifically   
   defined: sort of "about 400 nm".   
      
   When I had my natural eye lenses replaced with plastic lenses I was told   
   I would be ale to  a teeny bit into the ultraviolet, the plastic being a   
   little more transparent to it than my natural lens had been [*], but I   
   never did anything to determine to just what photon energy I could see.   
      
   [*] Of course, by the time I had the replacements done the cataracts in   
   my natural lenses turned everything a yellowish hue. When the bandages   
   first come off the first impression is that everything is intensely   
   bluish, kind of like those irritating auto headlights.   
      
   --   
   Dave Hatunen: Free Baja Arizona   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)