Ah yes, the old GE Circlite fluorescent tubes. They were a good idea ahead of its time but it was poorly executed in real life. I remember having one in the 80s in the garage and it always had trouble starting up. It did last a few years though before it failed to start for the last time.
Video related:
GE's bizarre early attempt at a CFL https://www.youtube.com/watch?v=JFJO3emhOyY
I used to work for an appliance maker at the factory depot for mainboards a long long time ago.
When we did a microwave control board repair, assuming we had that particular unit as a whole (as opposed to a simple test jig,) we'd put a big pot of water and a circular tube in the cavity. The water would absorb the majority of the microwave radiation to prevent damaging the magnetron, there was enough stray radiation in the cavity that it would excite the phosphors in the tube and light it. You could do something similar with small neon bulbs. I had a block with several embedded in clear microwave safe plastic, and you could see where the microwave radiation was by which bulbs lit.
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