The last time I did some reading was a year or two ago, but back then T-5s were a little more efficient than T8s (lumens per watt), and brighter, but much more expensive to buy tubes and fixtures.
At that time, T5 HO was MUCH brighter but (I think) quite a bit less efficient). And the HO bulbs either had a shorter lifetime or were expensive, or maybe both. I forget.
I thought at that time that T5s would only be worth it if I wanted the extra intensity or fewer fixtures. If I had planned to burn a lot of kilowatts, eventually the higher efficiency would "pay for" the initial price of fixtures plus tubes.
I was going to wait until T5s became the new "standard" and prices dropped, but LED lights make me wonder. When LED prices drop a lot, they will be much more efficient than T5s (I think). T8s might be the "low price point standard choice" until LEDs become cheap enough to replace them.
The old T12s are just so inefficient and low intensity that I would not buy another - I'd replace them with T8s unless T5 prices have dropped lately (or I found a good sale price).
