I like this chatter, it gives me what I'd need to make a decision on lighting to replace my hps. I'm not in the market yet but energy costs are getting to me. That would be my only reason to get off my 1000W hps.
There's no mention of t5's here other than used to use them and came from the Aquariums. I first encountered them in the elect. field in the 80's used for under counter or valance lighting. I new nothing of indoor growing at the time. I like the t5's, why the change to led's or cob's?
t5s lack penetration. good for germination and early veg and UV and IR supplements apparently but lack the power to go deep through the canopy unles u also use side/vertical lighting or put up alot of them
I am unsure whiche cob you are referring to. As far as lenses are concerned I have read that many lenses for COBs lower efficiency of light output in exchange for better spread. I would stick with 90s and get more lights and run them low if you can afford the initial startup increase.