How Does a Dimmer Switch Work?
Household dimmers are descended from the old rheostats and variable autotransformers used to dim lights in the theater. These were big sets of metal brushes that were pulled around wheels studded with copper and steel offering progressively greater electrical resistance. As the brush moved around, more or less voltage was conducted to the lights, which burned more or less brightly. The brightness or wattage of a light is determined by the voltage conducted to it multiplied by its resistance, or amperage. With direct current, which is what the theaters used, variable resistors worked just fine, although they were rather large and generated a lot of heat. Beginning in the 1960s, miniaturization and the development of the thyristors transformed the use of dimmers, and new inventions allowed fabrication of controls the size of a household light switch to replace the old 4-foot disks. These developments in electronics meant new improvements in television, film and theater lighting, but they also provided dramatic lighting opportunities for the home. Today, homeowners are offered programmable lighting consoles that musical theater technicians would have given a week's pay to have in the 1940s. All of this computerization, though, began with the dimmer--the part of the revolution with which most of us are familiar.
The thyristor and its lighter-duty cousin the triac are semiconducting devices. They control the amount of voltage that flows directly rather than by varying resistance like the old rheostats. Electricity travels in currents, and the currents contain waves of energy. Alternating current changes direction as it moves--it has "phases." The triac dimmer in most modern household dimmers "trips" off as the alternating current reaches the zero line of each phase. In other words, the triac simply turns the light on and off--about 60 times a second with 120-volt service. As the dimmer is turned down, the triac trips the power earlier in the cycle. The brightness of the incandescent light depends on how much voltage gets to the light. Dimmers can be used with any incandescent lighting (which burns because of resistance), and dimmers are being made for low-voltage lighting. Fluorescent and energy-saving compact fluorescent lights (CFLs) do not operate using resistance, but manufacturers are working to develop CFLs that can work with dimmers.
Most household dimmers are triac dimmers; they are rated for 10 amperes or less. They control one light or set of lights, like a chandelier or ceiling lights. Dimmer controls are available in the classic rotary knob that turns, slides and traditional toggle- or paddle-style switches. They are also available in remote control models, using infrared signaling to modulate the switching. Installation is as simple as removing the old toggle or paddle switch and connecting the new dimmer according to instructions on the package. For questions on which type of control is right for your use and installation, check with your electrician or home center staff.
