G'morning David, 

 DW> I found that the correct word is "photochromic" - becoming
 DW> (dark-)coloured in response to light. "Phototropic" is
used to describe
 DW> plants that bend toward a source of light.

Indeed, any reactive change in animate objects to light;  it came 
to my lips automatically.... 

 DW> In England, in my youth, it was possible to buy a special kind of
 DW> window-glass called "Vitaglass", which *transmitted* UV.
This allowed
 DW> you to get a tan indoors, which was considered to be a good thing back
 DW> then.

Mmm... the summer house on Jersey was so equipped, pillaged by the 
Wehrmacht and missing when we finally got back there in `46.

 DW> Brimmed hats are good at protecting the face from UV coming from above,
 DW> but are useless against UV that is scattered from the ground, snow,
 DW> water, etc.. I often wear a hat *and* dark glasses, except when the
 DW> temperature is so high as to make wearing a hat uncomfortable. Then I
 DW> carry a parasol.

New NZ skiiers are usually sunburnt up under their chins, nose and 
ears through not realising the degree to which snow reflects the 
sun....

 DW> Polarizing sunglasses have never gone out of style here. I think
 DW> they're a great idea.

I carry polaroid filters for the cameras ... but strangely never 
felt the need to re-equip myself with sunglasses;  sheer 
stupidity, that may well have been...but I have enquired at 
change-of-perscription time about clear polarised glass or plastic 
without success.

:-) 
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