-> This delay is MUCH longer than the time it takes photochromic lenses to 
-> respond. 
  
Many years ago, I fantasy-invented various devices that would use 
*very* fast photochromic glasses. For example, I thought of a foglamp 
that would emit a very rapid stream of very brief pulses of light. The 
user would wear glasses that would be darkened just as each pulse of 
light was emitted, and would then become clear, over a time of the 
order of a few microseconds, as the pulse travelled away. The result 
would be that the back-scatter in the fog, right in front of the lamp, 
would be blocked from the user's eyes, but the fainter light coming 
back after being reflected from fairly distant objects would be allowed 
through. 
  
I am sure that this would work, as would several other things I dreamed 
up, *if* there were lenses that would darken and clear fast enough. 
  
                     dow 
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