The problem with LED's is the lack of penetration. They have a very good lumen to watt ratio but no depth penetration. There are great high wattage great wavelength LED's. There are many systems on the market and most are scams and a waste of money. There is a bad rap from all these companies producing LED 'growlights' that don't have sufficient wattage, incorrect wavelength, wavelength balance within the light isn't correct due to a lack of research and just making up what appears good to the uninformed buyer. When they become better designed and cheaper, I'm sure many SoG and Lowrider growers will start jumping on board. In the meantime, it isn't very viable for most grow options and the cost isn't worth it for the actual product. You can't compare the yield of an LED light to an HID of the same wattage in any non(SoG/Lowrider). The HID will always out-preform and justify the higher electricity cost/bulb cost/cooling.
As LED's improve and research creates more effective LED grow lights maybe they'll become more viable and more people will jump on board. My problem is LED's are not new technology, they are old and have not progressed very far. They are a great technology but their use in agriculture is limited. I'm more willing to bank on a newer technology surpassing LED than research perfecting its use as an efficient/sustainable grow light.
p.s. NASA using LED's as a grow light is because it is currently the most viable option for their conditions. They aren't growing Cannabis as a cash crop where it's value far surpasses the need to avoid the inefficiency of HID's. I can promise you if NASA were trying to grow cannabis for production here on earth, they'd be using HID's and the like. Not LED's.
Just my 2 cents.