Multi Transistor Circuit
Electromagnetic Fields with free space impedance allows one to capture a tiny bit of current from your body acting as a dielectric antenna with some impedance to the amplified semiconductor switch to the LED.   

What comes out would be a half wave rectified pulse of light from the radiated low frequency grid voltage electric field in V/m.

Putting another finger in the middle could be shunting the Vbe to cutoff.

Electric field from a line in the wall will be somewhat inverse to distance and proportional to length of you and conductor as an antenna.







simulate this circuit &ndash; Schematic created using CircuitLab

maybe something like this