My seedlings are far too Spindly..

[murihikukid]

Hi..I bet this has been covered so could anybody please direct me to a post ...My seeds that I have propagated have always been very spindly and it amazes me how small plants in the shops have such thick stems so there must be a method for this...I have 40 seeds propagating now in a self watering propagator(Perosene) ...they are just appearing from the mix so I presume they are not far away from the crucial period of growth..As I understand it is temperature related ...At this stage they are under lights and have appeared far quicker than ever before even though I thought the seed raising mix looked like crushed coal??? ...
Thanks Ron