plants dont thrive on dark....they do require it , they thrive on light, food and water. if ur just using natural light then they wont produce great results. tomato food will help but its dependent on the npk ( u havent told us what levels they are). really need to see pic of tha plants mate and any other info u can; what kind of soil/medium are u using , have u just got them sitting on a window sill, how bigs the pots, what kind of plant/seed, anything and everything u can tell us will help us to maybe give u some advice. but for starters go and buy a decent light and timer. even 2nd hand will produce better results than on a window ledge. best of luck buddy.