Those plants are 30 days old. They look like they have had tons of leaf die and even look like they might have been topped or damaged which is why 1 now has 2 tops.The leaves are looking nice and healthy though. I don't see any apparent nutrient deficiencies. Sounds like you have ample light. Next question about the light though is how close is the light to the plants. Having enough light means nothing if it is too far away. Also what are the temperatures like? My room used to be cold and because of that my plants grew at a turtle's pace.
Without answers to some of these questions we can't really help you any more than to throw out general suggestions. The more information you can give us the better chance we can get you on the right track.Those plants are 30 days old. They look like they have had tons of leaf die and even look like they might have been topped or damaged which is why 1 now has 2 tops.
I as well suggested more light but the plant needs nutes. The op need sot improve growing conditions. Brushing off the fact the op is not using nutes will not help the op grow or his plants..
So to the op get more lighting. Start nutes. If you are not checking ph I suggest you get a meter or drops and start regulating the ph. Get a thermometer and regulate the temp and humidity. You do those things the plant should grow. And also explain what the plants have been thru. Why they look like they have been topped and why it appears tons of undergrowth has died.