Growing chesnut indoors?

Right now I'm growing two chestnut trees indoors, I found two sprouting nuts back in december and planted them in pots. One of them is already 20 centimeters high and has four developed leaves, the other had just come out of the soil. I was wondering, because in my room they get most of the afternoon sunlight, but not direct sunlight itself. Will this be enough for them to survive into spring, or should I help them out with a lamp?

Thanks.