In my curious youth, I sometimes played with NE-2 neon glow tubes, glass bulbs about 7x15mm with two wires sticking out one end. These cheap little lamps, only drawing 1 watt, were used as indicator lights in appliances and equipment (since replaced by LEDs). Their trigger level is about 85 volts. To use one on 110 VAC line current, put a 1 meg-ohm, 2w resistor in the circuit.
So: take a 2m- or 3m-long plug-in power cord. Solder the glow tube and resistor in series at the bare end.
Carefully tape over all exposed wires.
'''resistor
+--XXXXXX------------->
O
+---------------------> power
NE2
Plug into wall socket. Turn off room lights. Swing light around at end of wire. Enjoy the line of orange light. At certain rotational speeds, the line breaks up into dashes or dots. You're seeing the strobe effect.
And that's exactly what causes the dotted line in the photo -- strobing at line frequency. Experimenters out there might want to build this simple rig and try time exposures, eh? It'll be even more fun if you have a little multi-color-filter wheel spinning slowly in front of the camera lens.