There is a whole forum dedicated to this topic (the Growing Under Lights Forum) and there are many complex issues, but, for plants I grow under artificial light, I have shelves/benches with T12 fluorescent shop fixtures (Home Depot sells them cheap) placed side by side as close as they will go without modification. I use a combination of 4100K and 5000K bulbs (there's more that goes into calculating the optimal wavelength than one might think, but I've found something around 4500K works best for most of my indoor growing applications). If you need a large amount of growing space or have special requirements, you may need something a little more fancy, but the T12 fixtures are pretty cheap, the bulbs are pretty cheap, and everything is very easy to source.