IF YOU HAVE 81 PLANTS FOR ONLY 2X1000 WATT LIGHTS YOU WILL NEED ANOTHER LIGHT. THEY SAY ONLY 15-18 PLANTS PER LIGHT. i HAVE 2X1000 HPS OVER 20 LADIES, BUSHY AS EVER. IT WILL WORK AND YOU WILL GET BY BUT IF YOU WANT THE BIG YIELDS, GET ANOTHER LIGHT. IF YOU HAVE 2X100 HPS, GO AHEAD AND GET A MH LIGHT TO BALANCE IT OUT AND GIVE SOME BLUE SPECTRUM, LIGHT TO HELP WITH VEG( BUSHIER PLANTS) HAPPY GROWING