This Instructable shows you how to make a USB-powered LED lamp that turns on (and off) via the wave of your hand (and the QT113 IC):
The touch switch circuit is based on the QT-113 integrated circuit. It works by detecting changes in capacitance. When it is first turned on it measures capacitance at its sensor plate. When a human touches or comes near to the metal sensor plate the capacitance is changed and the circuit turns on.
The sensitivity is adjustable so that at a lower setting it will require you to directly touch the sensor plate. At its most sensitive setting, it will detect your finger through paper, plastic, glass, or even a brick.
The larger the sensor plate the more sensitive the switch. The sensor plate is the triangular circuit board at the front bottom of the lamp.