Hey, pretty late but there ARE ways. First way is to use the Cave Wells, which are the small spots that have light from the surface shining through. They are big enough that you can grow a good amount of food in those areas, things like rice that you can grow quickly and feed to your animals. Another way is a mod called Vanilla Factions Expanded: Insectoids. This mod basically overhauls being able to live only in caves. It allows you to grow mushrooms that don't require any light at all, and a mushroom that glows just enough to grow normal plants around it; basically an organic sun lamp. Not to mention this mods companion mod Caveworld Flora. It also adds plenty of plants and mushrooms to the caves for feeding animals. I'm sure there are other ways but these are the main ones that I've been able to use thus far.