Also...it's not so much that they need "twelve hours of light"....but that they need at least twelve hours of darkness. They can live in total darkness pretty happily. I've never heard of it causing harm. But constant light, with no "night time" will stress them out.
So, if there is light in their room in the day, just make sure they also get half a day of darkness. If they have dark tubs or live in a darkened room...they'll be fine.