Not to sound know it all ish, but this is really something we already knew. We know the necessary wavelengths that plants like, and are even narrowing down the supplemental wavelengths as well.
The problem is intensity which translates to penetration. In this we have not enough, which results in the necessity to scrog and be a bit aggressive with lower trimming, or suffer popcorn buds, or the intensity is entirely too focused/much which has resulted in stunted growth and bleaching.
It seem LEDs are working great, and are indeed very efficient, what we need is to lock down the correct relation of power, diffusion, and spectrum. Combine that with falling costs, and led is moving forward where hps is slowing to a halt. Though there are some very neat HID innovations coming out.
I would give led another two years, especially with the recent silicon chip advances. Things should get interesting.
Even with the spectral data, we are left wondering why if the desired light is so much more abundant in LED that a 600w system is so set it and forget it where as the led requires such attention to penetration issues and optimal placement. I think were close but not quite there to replace HID on a large scale. The spread and penetration of HID is just so great.