In reply to galpinos:
Unless they've changed now, the Chameleon used to go considerably darker but nit a slight as the Zebra (I have both). The Zebras are ok for brief trips over snow, but I didn't find them enough for all day on snow or glacier travel.
I've found the Julbo lenses much better than cheaper photochromic glasses, but the Smith IOS/IO photochromic lens is very similar to the Julbo zebra, with a similar price tag.