Why Is this happening?

140 W CFL
soil mixed with perlit ph range 5-6.5
bottom leaves are turning yellow and the stem a little bit black.
http://s11.postimg.org/fk3my9s9f/Photo0475_1.jpg

http://s27.postimg.org/x6jsrmzpf/Photo0476_1.jpg

http://s29.postimg.org/9ae1w1enb/Photo0477_1.jpg

looks like the leaves are crispy to me!!!

Have you fed them any nutes? What kind of water do you use, tap, RO, distilled?

Those are the single starter leaves. They die off rather quickly after the plant has established it's self.

Even though you did not post pics of the whole plant. From what I can see, your doing fine.

Don't sweat it. Continue on.
Water when you stick your finger into the soil to the first knuckle and it feels dry.

Good Luck