I bought the flat panel, I think it was 24 maybe more LEDS per panel. They stick inside the fixture with 3M tape, there are some that come with adapters that will fit a couple of different types of fittings.
I have a couple of fluorescent fixtures that I'm I am going to hard wire 3 or4 of the panels into.
Look for the bright white or daylight, they give a whole lot more light than the warm whites.