Hi guys. I will post my research and testing tesults, also my oppinion (IMHO) about optimal DIY LED lights.
What your plants really like - is constant flow of lots of lights energy, and in all that flow it likes most peaks of 450, 660nm
So, here is recipe for quality lights, which will give you good results for a price.
Let's say we're talking about 150W LED setup. We will divide all power into 2 groups - 100W and 50W.
100W may be used to get main full spectrum light fro white LEDs. Lets go further and analyse those white LEDs.
White LEDs are possible in "warm" and "cold". "Cold" has highest PAR and best ability to go "under leaves" on plant, also it promotes bushing, as it has many blue in it. Warm has more red, it is more suitable to flowering, but it alone will not give such good result. So, after some research i found, that optimal mix is 2 cold : 1 warm. I understand that you will think now "but in flowering you need more red" and you are damn right. That is why we will use another - colored diodes. And exactly, 660nm reds and 450nm blues. SO, we have 150W total, 100W of these are whites, what's left is 50W of colors. From that 50W of colors we need this mix: 40W of 660nm reds + 10W of 450nm blues.
In result what ve got is nice real full spectrum light with peaks right for plants.
150W total, 66W cold-whites (~6000K), 33W warm-whites (~3000K), 40W reds 660nm, 10W blues.
Also here are few other spectrums which could be added to mage lights even better, but they are not mandatory.
Green (~530nm) promotes absorbtion of all other lights, lenghtens internodes. This is why plants under HPS streches so much.
IR 730nm - regulates internode lengt, works on plant's raspiratory systems, recommended 5W on 100W total
UVB - promotes oil production as plant defence mechanism. Recommended 15W on 100W, mau be added byfluorescent UVB lamps, not LEDs.
Recommended LEDs, which gives good results: Cree, Philips Lumileds. Philips Lumiled rebel are really great and maybe even best, but slightly expensive. But it works for the money.
There are methods on reaching higher lm/W by putting LEDs in partial power. On 30% load some chips gives out up to 200lm/W. It is great and everything, but it takes several costly chips instead of 1. ALso it has much longer life. Very much.
Main thing in LED setup is cooling. Bigger are the radiators - the better. Absurdly huge radiators are the best

Chip temp pays very important role in lm/W output and even bigger role in LED lifetime. Cooling is even more important than LEDs which are used, i'd say it's number one importance.
That's it. These are results from more than a year of my research, personal testing and discussing with other growers.
Hoping that this post will be useful to somebody.