How Dimmer Switches Work

Finally someone explain how these things work

Today, modern light dimmers are much different than old dimmers from the mid-20th century. In the good 'ole days, dimmers employed resistance: that is, a piece of material was "blocking" the electrical charge. Not only did this not work very well, but it was also expensive, created wasted energy, and was potentially dangerous. Luckily, a new way was invented to dim lights.

Most modern dimmers use what is know as Silicon Controlled Rectifiers (SCRs). What this device does is limit the power to a light by quickly switching it on and off. In essence, it chops off part of the power voltage. This reduces the total amount of energy that flows through the circuit, and is much more effective.

Cycles of light

Electricity is made up of a current that flows in one direction, and then the other, at a rate of 50-60 cycles (called hertz) a second. In the middle of the back-and-forth flow is a 0 point, or the point at which no electricity is flowing in either direction. It is at this point that a dimmer is synchronized to turn "on" or "off." The effect is smooth dimming, rather than flickers of light. The power device turns "on" or "off" every time the crossing point is reached.

What makes it happen?

The magical power device responsible for this? A triode alternating current switch (triac) or Thyristor. A trica is a small semiconductor that is bilateral in movement, while a Thyistor is unilateral in movement, hence two are needed. Both of these act as a voltage-driven switch.

Set the lights to dim

Moving the dimmer switch knob pivots the contact arm, which increases or decreases resistance. When set to "dim," greater resistence slows down, or holds up, the current. On the flip side, when turning the lights up, the current is "let go," with little resistence to its normal function.

Keep it under control

Some dimmer controllers use a microprocessor with an analogue circuit. More modern and high-tech systems use a digital dimmer, rather than an analogue circuit. These microprocessors are more reliable, are quieter, and produce lower costs.

What's that buzzing sound?

One of the drawbacks to dimmer switches is the slight buzzing noise that often accompanies them. This is caused when there is a sudden shift in voltage being passed through the current. There are two things that can help stifle the buzzing in your dimmer: an inductor choke, a length of wire wrapped around an iron core, or an interference capacitor. Both work well.

More information on dimmer switches