yea them bottom leaf`s that begin to turn yellow, remove em when they are about to fall off them self, when you dont have to pull hard for them to let go .. they have done there job and provided the plant with the food its need and is now ready to fall off, like "normal" plants out side at fall ..
leaf`s is the plants power engine, it make the hole process that make the plant grow/grow buds, remove them and you dont only stress the plant but you also taking away some of its grow potential and the stored food the plant have safer in them for later ..
also, plants is`t stupid, been doing this for millions of years, and they got a few tricks up their sleeve, like the light they use is mostly in the blu, red and yellow spectrum, them we cant see much of, but plant have adapted to it and the leaf`s actually let good amounts of that colored light through there leaf`s (only color they seems to block out is green, the only one they really don't use) so under grow get way more light then we think, the shades we see plants don't see in the same way (been reading a long article about it, but cant seems to find it agin)