You can take a 40 watt fluorescent bulb and walk under high power lines
and it will light up bright.
That's RF.

Bob McConnell wrote:

An NE2 neon bulb and a three inch steel coil spring about the same
diameter. Connect each end of the spring to one of the bulb contacts.
Don't know how sensitive it is, but the Navy provided one on the end
of a broomstick to reach into the transmitter room to detect HF before
entering. We never got hit, so I don't know how well it worked.

Bob McConnell (Ex-NFIT)
N2SPP