its all about the equal coverage of lumens more than the watts. In veg, plants require less lumens than when flowering. Depending on the size of the space you are dedicating to garden, use 250w metal halide (blue spectrum) in a closet or a 400w MH for every 4sq'. When flowering 600w high pressure sodium(red spectrum) are hands down the most efficient lumen/watt light on the market. ie. 1000w creates 115,000 lumens vs. 600w creates 90,000 lumens. Thats 115 lumens per watt vs. 150 lumens/watt. With the expoential loss of lumens every foot the light is distanced from the plants, 600w can be placed closer than 1000w and ultimately supply more lumens cheaper and with less heat especially using a light mover can get you even closer. 600w cover approx 5sq'.