Thanks for the reply Phone Wind.
Actually, what you said kinda answers my question but also kinda reinforces it because
all Serengeti lenses are photochromic to some degree (just do a google search for Serengeti and photochromic, also mentions it on their website). When you say the Velocity gradient lenses I assume you mean the Velocity frames with Drivers Gradient lenses and according to the Serengeti web site they vary from 9% light transmittance to 24% light transmittance (for both the Drivers and Drivers Gradient), and the spiel at the bottom of the page says they adjust to the changing light.
http://www.serengeti-eyewear.com/tec...ns_drivers.cfm
However you say that by pretinting the photochromic lens they can be made suitable for driving/flying. Which I assume is the case with the Serengeti's in that they only go up to a maximum light transmittance of 24% (or less on other lenses). In which case they are not fully photochromic and are thus ok?
Am I making sense? Maybe I'm getting to techy with it and should just accept that they don't vary much so their ok to use...nuff said
(The Serengeti site also talks about the photochromic properties being impregnated during the firing process rather than using a silver alidade coating, so I wonder if this means they don't suffer from the problems you mention with the windscreens filtering UV)