Dr.King:
This has been an idea of mine for some time but I am always so skeptical when it comes to cheap LEDs. Are you just getting a generic brand off ebay? Just to clarify, you're using the LEDs two on a side on the short side of the HID lighting, so it's basically boosting the dimmer parts of the HID spread?
Naw I usually go with Grow Bright Led UFO's which are $68 instead of the $50 ones that have the same similar look and seem to deliver exactly the same results that I've noticed. Used both, it's just the Grow Bright Brand will last a lot longer without needing to use the warranty. I've had one of the $50 ones blow all of its lights in 6 months which sucks waiting for a replacement so I have back ups. I switched to Grow Bright because I have been using the same 8 for over 2 years now and only one burn't out. The burn't one just went a few months back so it lasted 3 times longer then the other brand. Their warranty services(last 3 years) are better and faster also.
Indeed you are correct I supplement my main 400 watt system with 4 Led lights, 2 on each side. They are all spaced one foot away from my main light so they are 1 foot or so from the sides and the other Led lights. Seems to cover a big 5' x 5' easily and if my Led to watt conversion is right, with 400 watts and 4 138 watt Led panels it's around 1250 watts. Which makes for less hate, less stress, less bills and better quality buds in my opinion. 9 spectrum's is about the closest thing to the sun so that is what I will give them until I can grow outdoors in a sealed Green House . I also recommend the Co2 Bags that they sell on Ebay. Before and after results with a Co2 bag added 10% more to my yield which is nice for just a bag that costed 20 or 25 dollars and last 6 months(2 flowering sessions). Best of luck to you man.