Your plants are stretching..(when a plant stretches it means its stretching for more light).If you cant afford a HPS, or MH.. Go to the hardware store and buy a pack of 23 watt CFL's, and buy a Y splitter, and your plants will appreciate it... Dont water your plants until there almost dry..Veg for about 6-8 week's under 18/6..Depends on how there growing...Than when its time for 12/12, get a HPS...
Good Luck!