digital ballasts
 

LEDs, short for Light Emitting Diodes, are tiny semiconductor chips
that generate light when electrified. It takes a small amount of
electricity to make an LED glow (emit electrons), and the elements
that the diode is made from determine the light spectrum it emits. An
LED is backed by an internal reflector and encased in an epoxy body
with an integrated lens. Together, these components determine the
angle of the light emitted by the diode, which is shaped as a downward-
facing cone. Individual LEDs produce relatively small light cones, so
they are clustered into arrays so the light cones overlap, increasing
light intensity and coverage area.


a href="http://www.eclipseledcompany.com/
Digital_Ballasts.html"Digital ballasts/a

The 600w is the most efficient light in lm/w. I think it's called Son-T Agro plus or something. I have a chart I could send you...

you could get 1/4 pound every 2 months with a 400w HPS, a 600w would get you there faster. You should easily be able to fit 6 buckets in a tent that size. I have a tad bit smaller tent, and I can get 5 BIG 7 gallon buckets in there.

Analog ballasts take a little bit longer to warm up, Digitals are quicker. They're also supposed to last longer, and yes, they should be more efficient.