florescent lights(tubes)...I got mine for early growth but stuck with em....the great thing about them is you can put them close to the plants, opposed to hps... they give a good amount of lumens....stay cool, dont make noise, and low wattage....it was 100 dollars for my 4000 lumen(2foot, 2bulbs)... one mh one hps bulb...the farther plants are away from light the less lumen(x10 per inch) so the argument is since t5's can be closer the lumen output isn't that much less than those hps....i would recomend a four foot 4 bulb if you can afford it....you can buy it for like 150....