I only utilize ambient room light from windows (& no direct sunlight hitting any cages, ever). Most snakes don't appreciate bright lights anyway. In winter I'll use
red or black bulbs for extra overhead warmth for certain snakes though.
By enforcing a 12 hour light cycle, I assume you're trying to prevent your snakes from going off feed for seasonal changes (as snakes are known to take the "hint"
both from temperatures and amount of daylight)? I stick with what nature supplies, & I only have 2 snakes that go off-feed in winter (neither are BPs, FYI).
I don't use CHE here but that's another option for overhead heat without adding light. You still need to regulate them- just like lights, they can easily over-heat
the cage & you don't want to "cook" your pets.