If you do "dive" on a cloudy day you may be in some trouble. My lume gets some use if I wake up and glance at my watch, no risk involved there.The lume on this watch is average to me. The lume is readable at 5am, but my eyes have also adjusted to the darkness enough that the slightest glowing object would be viewable. I have let a few watches basque in the sun on a window ledge all day. Never hurts to give your lume a workout.