the ballast.
cdm/cmh/lec are all the same, and really is really nothing new as far as bulbs go. its what it driving them that make them what they are now.
those lines you see in pictures/videos of an hps(sine wave high frequency ballast) grow is the bulb flickering so fast the eye cant see it, but is really only producing light half the time that its actually running. the square wave low frequency ballast runs the bulb 100% of the time.
although this vid is about hps lighting for horti, now using low freq square wave ballast in their 1000 watt, it explains what is going on that makes the lec such an efficient light compared to a sine wave high freq
*i used cmh bulbs in my 400 watt for years. better than running horti blues imo
*apparently there are companies claiming square wave, that's aren't so. I'd do some research on that company. Also there are conversion kits so you can run on your current hid hood.