The easiest and most cost effective over the long term are LEDs. If you want to get more involved,
hps are powerful but require ventilation. I'd just go with a plug-n-play, high intensity, full spectrum
led lighting system. LEDs are really efficient these days and last forever. Try
uponics.com for a good list. I have the G8 LED, but want to get the California Lightworks newest model as I expand my grow room.