I need to replace the 4 4' lights in my greenhouse. At the moment I'm using regular florescent grow lights. Would it be better to change them to T5 or T8?
Switch to LEDs. The fixtures are a little more expensive to buy but the savings just in electricity is dramatic.
Fluorescent tubes need to be replaced yearly because light output drops. You can't see it, but the plants do. LEDs last much longer. People need to consider this when calculating costs.
__________________ May the bridges I've burned light my way.
Definitely get LEDs. Buying multiple fluorescent fixtures now would be like buying a 5 year old cell phone for only a little less than the brand new model would cost.