I use the 4 ft bulbs, but here is a better UV source… 
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I am using that brand t5 bloom, veg, and the 10k tubes now, and have a two tube 2 foot lamp that is not being used presently. I came very close to using those t5 uv tubes.
But I chose the more forgiving LED UVA only that HLG had on sale for $95. Since the the t5 UV tubes are about $22 each, and they have a short lifespan. Also you need to be much more careful with the UVB that the t5 produces.
I once used the big fluorescent UVs back in the stone ages, (1980s), and it made the weed very harsh. I am sure that I overexposed the plants, but I am still gun shy of UVB.