The ELECTRON-O-SCOPE™ uses a Field Effect Transistor (FET) which responds to both positively and negatively charged objects. The intensity of the LED is proportional to the amount of charge detected by the instrument. Positively charged objects brought within one meter of the probe will cause the LED to glow. Not only does this instrument pick up the static charge produced on a glass, plastic, or rubber rod, but also on the material used to produce the charge. The electric field produced around a computer monitor or TV set is easily picked up as well.