A touch lamp is a lamp with no external switch that is designed to be turned on and off by a human touching any part of the lamp. Other than the switch configuration, little separates the average touch lamp from the average lamp with a manual switch. In a touch lamp, the electrical switch that turns the light on and off is inside the lamp, not outside. This electrical switch is wired to a circuit and the circuit is wired to the inside of the lamp's external layer.
Touch Lamp Switch Configuration
Changing the Lamp's Capacitance
Everything has a capacitance; that is, a certain capacity to hold an electrical charge. Size, form and composition affect levels of capacitance. The human body has a different capacitance from a touch lamp, and the human body and touch lamp together have a different capacitance than either one individually. The circuits wired into touch lamps have the ability to detect these changes in capacitance, so when you touch a touch lamp, the circuit activates the electrical switch. When you take your hand away, the lamp goes back to its original capacitance so that it will be ready to detect the next change in capacitance and activate the electrical switch again.
How Touch Lamps Control Brightness
Many touch lamps can emit light in multiple brightness settings without the benefit of three-way light bulbs. When you touch these lamps, they don't just cycle off and on; they go from dark to brightest to second brightest to dimmest. When the lamp is set on these dimmed settings, the power source is actually turning itself off and on in rapid succession. By cycling off and on many times per second, the light level appears to the naked eye to be consistent. But because the light bulb is not getting all of the power it would be getting if the electricity were on constantly, it does not shine as brightly.