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I made a useful discovery today.  Apparently the process that makes my Transitions lenses get darker is exothermic (and the lightening process is endothermic).  The glasses get darker faster if the lenses are cold, while they stay dark for a long time after going indoors if they are still cold. 

If I warm the lenses under hot water, they'll lighten much faster than if I left them alone.



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Jan. 25th, 2008 07:51 pm (UTC)
I have Transitions lenses and have noticed the same thing. Glad you've confirmed that I didn't imagine it. It makes them work really well against snow glare, but not so well on hot summer days. I'll have to test in summer (if it ever comes back) by chilling them before exposing to the sun.
Jan. 25th, 2008 08:32 pm (UTC)
Faster reaction rates at lower temperatures are not a hallmark of exothermic reactions. Both exothermic and endothermic chemical reactions tend to proceed faster at a higher temperature. The reason why the darkening process might take place faster at a lower temperature is because the reverse reaction (which probably is always taking place, even in sunlight) is slowed, thus allowing the sunlight to change the material into its darker state faster.
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