Need more info man.
What's your temps look like?
what kind of soil is that?
did you add anything to the soil for aeration?
what has your watering schedule been?
what kind of lights are you using? looks like incandescent bulbs (very yellow). im gonna give you the benefit of doubt and guess they are cfl's.
From what I can tell, it looks like bad soil to start with. don't see much perlite in there, and you should have a bit. i mix 1/3 perlite into the soil before i plant. helps with drainage and aeration. Next up, those big pots are too large for small plants. they can't possibly drink anywhere near as much water as the soil could hold. At that size mine would still be growing in plastic cups. try to let it dry out between waterings.
I noticed they are dying from bottom to top. leaves are yellowing and falling off? I've found that to be a symptom of heat stress more than anything. sometimes root rot too, or a mixture of both. PH issues can cause similar issues as well. If it is way off for too long, you get nutrient lockouts that take FOREVER to get better. Depending on where you live, rainwater may not be that great. better than the tap, but it can contain all kinds of contaminants itself.
If those are cfl lights:
A note about your lights- those metal reflectors aren't that great. CFL bulbs don't NEED reflectors, as the intensity of the light fails after a few inches. those metal reflectors actually absorb what little heat the bulbs and ballasts eminate. I would recommend removing the metal reflectors and getting the actual bulbs with 2-3 inches of the plants. just remove the reflectors. the fixture is far more mobile without them anyway.
This looks very similar to my very first grow a looooong time ago. I had 99 problems at once, and a very slim survival rate. Mostly due to not understanding my own setup fully.
Please post as much info as you can, and everyone here will try their best to help you get your plants to topple themselves over with budses.