Thanks, as I want brutal honesty in all the answers.
What's good is that the LEDs "supposedly" save about 50% in energy costs (they say). What's bad is that I don't see how that can happen given we're still using the old T12 ballasts, which controls the current, right?
What's really bad is that the T12 ballast will burn out the T8 LEDs quicker (how quick? Dunno.) so maybe I don't get the long life either.
One really good thing is that overdriving these LED lights makes the garage light up like daylight now. It's amazingly bright with 16 of these LEDs in place (actually, only 12 because one fixture has one or maybe two bad ballasts).
I measured with a ruler. a. The T8 LED is actually 1 inch in diameter (8/8ths). b. The T12 40W fluorescents are only 1-3/8ths (so it's actually a T11)
This is a good point in that the original T12 ballasts are due to die sooner than the LED bulbs will die, especially since the original ballasts are so old that they're made in the USA (which means they're really old).
And when the original ballasts die, the T8 LED bulbs will be useless.
I think I really have only two decent choices, given that cost is a factor (although saving on electricity is also a factor).
1. Buy a whole new LED fixture (the color of the existing LEDs is fantastic) 2. Put a T8 electronic ballast into each
I just want to get rid of the buzzing of the one bad fluorescent ballast, and to rid myself of the bulb-changing hassle once and for all, but not at too steep a price.