They sit in direct sunlight on my valve stems all day and when the sun goes down they lose their glow faster than it gets dark. You didn't think they should glow because you could never capture their glow. I took out the Black Lantern overnight to charge it, but by the time you finish the fourth, the first one stops working. It's possible that if you drive through a line of black lights, they'll glow for several feet, but that's impractical.