The goggles have a very sensitive LCD screen situated behind the lenses. When you expose the goggles to sunlight, the sunlight can potentially burn that screen (think of how a magnifying glass lens acts in sunlight).
so the goggles lenses should never ever be exposed to direct sunlight. Not even for a moment.
but, for practicality, how do you manage that when you are flying around in the sun? I use something like this when I have to take the goggles off
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people get those lanyards and let the goggles hang around their necks. I use one too, but tie the lanyard/neck strap to the goggles in such a way that when you take the goggles off they hang down with the lens side against your chest/abdomen.
one other thing that may help is attaching one of those battery clips to the head strap so that when you take the goggles off and let them hang around your neck the battery weighs down the goggles so they just, on their own, hang with the the lens side against your body.