They say it's not necessary, or beneficial to provide full spectrum/UVA/UVB lighting for snakes, especially those that don't generally bask, or those that are crepuscular or nocturnal. I beg to differ. There's more to it than just UV exposure.

My concinnnus got full spectrum lighting inside, and summer basking quarters outside during the summer. They lived to be 18 and 21 years old.

So now I got a Puelban milk snake. (I know, it's not a garter, but I'm making a point here) Every husbandry tip I can find says that these snakes do not need UV lighting, and probably won't use it anyway since they are crepuscular or mainly nocturnal and do not like bright light. Native habitat is arid, high mountain, Southern Mexico.

Anyway, with only dim ambient natural light coming in through a window, this snake hid most of the time, only rarely coming out after dark. I got (practically stole) a couple of Reptisun 10.0 bulbs (15watt linear florescent) for $3 each and started using it on her enclosure for 12 hours a day. I did not change the day/night cycle, and I did not change the temperatures in any way. Night get's down to 65 or so, and daytime gradient is 70-85. Flash forward 5 days into using UV lighting:

She's much more active, day and night. She does sit out under the bright light, warming herself on the undertank heater. She eats with more enthusiasm.(around sundown) Her attitude about being touched/held has improved. She actually watches me and the dogs during the day, instead of cowering and hiding, which is nice 'cause she's really nice to look at. Overall, she's acting like a snake should act!

I do acknowledge that the same thing could possibly happen without any UVB/UVA output, and just full spectrum visible light with a regular day/night cycle, but until I see evidence that it (UV radiation) is harmful, the lighting will stay. If it bothers her, I figure she'll hide from it, but that's not happening. Just the opposite is happening, and this is from a crepuscular / nocturnal species. Just imagine how your diurnal garters could benefit from the right lighting spectrum!