If you've got an account on overgrow you might recognize my username. I'm one of the first people who gave LEDs a shot, and I must say that for 99.999% of people, it's a waste of time. I'm not trying to be a pessimist, I'm just... Well, here, let's simply put it in perspective.

Do you take a HPS lamp and plug it directly into the wall? No, you don't, you plug it into a piece of fancy electronic equipment called a Ballast. Well, similarly with LEDs, connecting them directly to a power source without any driver circuitry will not get you the kind of plant growth you're looking for.

So the key problem is the ballast. Ballasts for LED lighting of plants don't actually exist, so you have to build one. This is why for 99.999% of people, it's a waste of time. You need to be an armchair electrical engineer in order to throw together something that will give you results.

If you want to build your own ballast (pulsed DC, PWM), here are my suggestions:
- variable frequency from 2kHz to 20kHz (honestly, a set 20kHz would be fine)
- variable pulse width from 1% to 10% (this is required, as hopefully you'll have the ballast long enough that you'll be able to use it with different types of LEDs, which may have different tolerances to high current pulsing. Being able to back down the pulse width will keep you from frying your LEDs)
- selectable constant current in multiples of 20 mA, from 20mA to 500mA.
- multiple "channels" which can have their pulse width and frequency adjusted independently.
- A very accessible on/off switch, just in case.

The best way that I've encountered to do this type of thing is by basing it around a PIC microcontroller. The easiest of course is the PICAXE ( www.picaxe.co.uk ) which can be programmed in BASIC and doesn't require special programming hardware to use. You use the microcontroller to take care of frequency and pulse width, you use JFET transistors configured as current regulators (see here) in order to handle current regulation.

So if you're the EE type, by all means. Get some 730nm, 660nm and 430nm LEDs and get crackin' on that ballast. (note: 470nm and 640nm could be added as well)