Its because the diodes are reliably pulsed or something at a max wattage of say 1w or 2w or 3w. But you can't continuously run them at that wattage or they would very quickly burn out. 1w diodes are the most efficient with turning power into useable plant light and little heat waste, but they lack penetration. 3w diodes are what are used in the best now and they run anywhere from 50-75% of that 3w depending on what wavelength and diode/company used. A 3w diode may not be as efficient as 3 1w diodes, but it will have a better footprint/penetration than the 3 1w (this is why a panel of 3w is better than 1w). My 395w panel is about 18w into 6 fans and the rest into 252 3w diodes (several reds, couple blues, white, couple orange, whatever and it ends up to 12 wavelengths). It is definitely much better than my 400w Super HPS with digital ballast, and I imagine could spar with a 600w HID even.Also saying a 400w HPS and a 600w HPS are similar is ludacris man, a 600w HPS puts out double the light of a 400w.
Also, Iv read alot of people saying they use like 200 3w LEDs but only pull like 280w of power...whats the point of the 3w LEDs then?
EDIT: Must be a shitty 1000w MH you have...
I don't mean to say most HID light is useless, some wavelengths are not as useful as others, but it is true that a lot of the power going into MH/HPS is wasted as useless lumens/heat/wavelengths that are not useful to plants (and this is where LED can get better than HID because you can eliminate so much of that waste (75% less heat watt for watt as HPS it seems too, thats a lot of power going into light instead of useless lumens or heat like with HID).