Don Wiss wrote:

What isn't clear is what do the new LED bulb drop in
replacements do with the ballast still being there. I presume they have
some way of ignoring it.

All a ballast is is a transformer to raise the line voltage and a current
limiter to prevent the fluorescent bulb from creating a direct short. The LED
drops will just have an internal step down transformer. They lose a little
efficiency from the step up/step down process compared to line voltage LEDs that
just step down.