Overview of the Dimmer Switch

By raising or lowering the lamp’s root mean square (RMS) voltage, dimmer switches can vary the mean power to an electric light source, intensifying or diminishing the brilliance of the light in the process. A popular installation in domestic settings where dimmers are often located in lounge or dining room areas to subtly alter the mood, they can be used with a variety of lighting technologies, including LEDs, halogen, resistive incandescent and dimmable compact fluorescent lights (CFLs).

Although small dimmer switches are widely used at home (sometimes with remote control features), larger installations such as cinema auditoria, theatres and architectural lighting systems are usually controlled using digital equipment such as the Digital Addressable Light Interface (DALI) and Digital Multiple X (DMX). More recently these technical standards have been integrated into Ethernet control systems.

A more specific use of dimmers beyond domestic boundaries is in the creative industries, where sensitive control of lighting is an essential part of manipulating the mood of the audiences. In this context, the technical vocabulary used to describe the alterations in a lighting system’s intensity are termed ''fades'': the digital dimmer switches used to control these systems produce either a ''fade up'' or a ''fade down'' and they can alter the intensity considerably faster than mechanically-operated dimmers. A prime example are ''house lights'' in a theatre that are often called upon to ''fade up'' or ''fade down'' with great rapidity. 

Recently, the older variable resistor or rheostat technology used in early dimmer switches has given way to much more efficient silicon-controlled rectifiers (SCRs), which dissipate considerably less heat.


The African-American inventor Granville Woods, who was also one of the first Black American electrical and mechanical engineers, is credited with inventing the first “Safety Dimmer” for use in theatres in 1890. Before his invention, dimmers were manually controlled via cumbersome dimmer panels which generated a good deal of potentially hazardous heat (fires were not uncommon).

Between 1950 and 1956, the technology used in these switches took another turn with the development of the Silicon Controlled Rectifier (SCR), a solid state semiconductor device also known as a thyristor. Much more efficient than their predecessors and less dangerous in that they generated considerably less heat, they also opened the door to the use of analogue remote control systems. Even so, because each individual dimmer required its own control wiring, in large installations a vast number of wires were needed to run between the lighting control centre and the individual dimmers.

Larger scale lighting systems today employ digital control protocols for the dimming function, as mentioned in the overview above.


Technical aspects

Thyristor switches are still in use today to control the dimming function in lighting circuits and offer virtually immediate dimming thanks to their ''switch'' feature: when the alternating current’s half cycle begins, the thyristor switches on at a variable time.

More recently, since 2004, a new generation of relatively lightweight sine wave dimmer switches have been developed which incorporate inexpensive insulated-gate bipolar transistors (IGBTs). They cause much less interference and are far lighter than thyristors.

Larger scale lighting installations typically employ remote control systems, although analogue dimmer systems continue to require a large number of wires: each separate dimming channel needs its own wire, each of which carries a voltage ranging between zero and 10 volts. Since the 1970s, serial analogue protocols have gone some way to solving this problem by multiplexing several analogue levels into a series requiring just one wire.

However, digital protocols (e.g., DMX512) have proved the way forward for most large-scale installations since the 1980s, while today digital signals are converted straight into dimmer control signals by means of microprocessors. The newer technology can provide lighting controllers with digitally-conveyed troubleshooting feedback in the event of faults and enable much closer control over fades.


Where the dimmer switch is used

Although they are widely used in domestic settings to create ambient lighting effects, in larger scale installations dimmer switches tend to be located together in easy-access racks. In architectural installations - such as external illumination effects to highlight the skyline of city buildings - electricity from the dimmer control is conveyed directly to the lights via fixed, permanent cable runs that cannot subsequently be altered.

Cinema auditoria and theatres especially need more flexibility than this hard run wiring system can permit in order to emphasise various dramatic effects. Circuits are run not to the dimmers but to a patch bay which is capable of connecting dimmers to different circuits. However, more recently, patch bays have given way in modern or refurbished theatres to patch dimmers and dimmer-per-circuit arrangements whose channels are controlled by computerised ''soft patches''.

How the dimmer switch differs from other switches

Although there are numerous devices capable of varying voltages, the term dimmer switch is reserved only for a device that specifically alters the level of voltage in a lighting circuit.