Mine are in complete darkness at night, I have no additional lighting for any of my snakes. Even "in the wild" there are nights without a moon, and I'm sure they function just fine.
I think besides just moonless nights, another thing to note is their tendencies to live in burrows of rodents or hunt in them. Which can sometimes be really deep. In these tunnels there would be no light, but they do fine, finding prey or chilling out