If that fixture is a 4' 12 tube HO (54W tubes emitting 5000 lumens each) you will actually be using more power than the MH--12 54W tubes are 648W. However you will also gain lumens with the fixture. Most 600W MH bulbs emit about 55,000 lumens. The MH bulbs are always lower in lumens than HPS of the same wattage. Ultimately both the MH and T5 will put out about the same lumens per watt, with the T5 being a tiny tiny bit better, but around 92 lumens per watt. I am currently running a 2' 12 tube T5 that boasts 30,000 lumens from 288W, but do not have a light meter to verify. But if that number is correct it puts the T5 over 104 lumens per watt.
To my mind, the biggest advantage with T5s is that having the long slender tubes rather than a single large one is that it spreads the light better over your spacer. And because the heat is spread over a larger area, it is easier to control the heat. This also means that you can get the light right on top of the canopy. T5s do not however have as great a penetrating power as the MH. This may or may not be an issue. My vegging space is only 4' tall, so I do not veg plants until they are monsters, so, non issue. However if you want to grow monsters, the T5s do lose lumens quicker over distance than the MH. That being said, I love my T5s (have 3 of them) and cannot imagine ever going back to MH.
However, your last line confuses me. If you have 9000 lumens per sq ft and a fixture that emits 60,000 lumens, that means your vegging space is only 6.66 sq ft? Since a 6.66 sq ft space is not even big enough to get a 2' x 4' (8 sq ft) light into, I have misunderstood something somewhere, but do not know what it is? Can you clarify? What size is the space you are planning on using the T5? Is the light a 4' 12 tube fixture? Can you link the light?
so I bought a staple gun and the black and white PVC plastic and tuck tape and I made an encloser for veg. Only down side is it's cold doesn't hold in heat like a tent does. It works sp far . Cost $45 to make. That's with tools/supplys
