A touch lamp is a lamp that can be activated by simply touching the lamp, rather than flipping a switch. Touch lamps are commonly used as nightstand lamps because it is so easy to turn them on in the dark. Typically the entire lamp is touch-sensitive, including base, neck and lampshade, all of which are metallic.
A further advantage of a touch lamp is that it can turn a standard light bulb into a three-way bulb. Tapping the lamp once will cause the bulb to glow at 33% of its rated capacity; tapping it twice brings it to 66%; and a third tap results in full wattage. A 60-watt bulb, for example, can be used as a 20-watt, 40-watt and 60-watt three-way bulb. In this way the touch lamp provides handy low-light conditions for eyes that have adjusted to the dark, while offering brighter conditions for reading or dressing, all from a standard light bulb.
The design of the touch lamp is another plus, making it durable and reliable. External switches on traditional lamps can become dirty over time, filling with dust, sloughed off skin cells and oils. A gummed up switch can eventually render a lamp useless, or at the least, make it unpredictable. Touch lamps, free from external switches and barring physical damage, continue to operate like new for the duration of their lives.
As to potential disadvantages, a touch lamp might not be ideal where it is likely to be prodded, pushed, handled, or inadvertently contacted often, such as next to a computer or on a desk, as it can be annoying to have to “tap it off” each time. A passing pet cat can also activate the lamp, wasting electricity. One way to avoid the latter situation is to use a power strip with an on/off toggle switch, and toggle off power before leaving home. Unplugging the lamp also works but is more trouble.
A touch lamp operates on the principle of capacitance. Capacitance refers to the capacity of an object to hold electrons, or an electrical charge. Alternating current (A/C) switches inside the lamp are affected by touch because a person's body is made mostly of water and is therefore a fair conductor of electricity. When you touch the lamp an oscillator responds to the change in charge and this activates the switches to toggle the light on or off.
Touch lamps are available at reasonable prices, starting at under $20 US Dollars (USD) and are available everywhere lighting fixtures are sold. Department stores and home improvement depots also sell touch lamps.
