This is on a Blue Mk2 with the brightness at a little over half way up

You'd definitely need to turn the brightness all the way up to read the display in direct bright sunlight. Doing so won't cause any burn problems with the VFD, as long as you don't leave it on a static image for days at a time.

I use the player (in the car) on 100% during the day and 80% at night. I rarely experience any kind of viewing problem (on either amber or green, depending which player I'm using - going to change the amber press player to blue soon though, as it looks better in photographs).

Rob