These devices are used for lowering the brightness level of your lights. The basic concept works by manipulating the applied voltage waveform to the source. By changing this, the intensity can be lowered or increased as desired. There are a number of uses for variable-voltage devices such as these, and are often referred t as dimmer, but mainly describe those for output control for halogen, resistive incandescent, LED and compact fluorescent lighting. When it comes to lowering the intensity of arc, mercury vapor or fluorescent forms, it requires specialized equipment.

A dimmer varies in sizes, from that of an average switch in homes to units with higher power used in architectural lighting or theatre environments. Generally, smaller domestic style devices are controlled directly, but there are systems with abilities to be controlled remotely. Today, professional products are often digital systems, including DALI and DMX. More modern systems commonly use protocols combined with the ethernet.

The intensity level is referred to as ‘fades’ in the lighting industry, and have two paths, ‘fading up’ or ‘fading down’. The speed is limited on manually controlled units, but with the introduction of digital units, this issue has been greatly removed. However, there may be reasons to avoid rapid brightness changes, such as the lamp life.

In the past, dimming devices were produce from variable resisters, but modern products use semiconductors. This increases their overall efficiency, as variable resistors dissipate the power like a voltage divider. However, due to the ability of rapid change, semiconductors allow the quick transition between on and off states, dissipating a small amount of power compared to the variable resistor approach.


Large panels were originally used for the dimming process, requiring power to travel through the control location first. This proved to be inconvenient, inefficient, and risky due to larger and higher power systems.

In 1896, the “Safety Dimmer” was patented by Granville Woods. This product lowered the energy wasted by lowering the energy amount created to match that of the desired intensity.

In 1959, the diode-based invention was created by Joel S. Spira, who founded Lutron Electronics Company in 1961. Additionally, his tapped autotransformer was able to reduce energy usage and enabled the feature to be used in standard electrical wallboxes.

In 1966, the light bulb socket adapter was patented by Eugene Alessio. This allowed the lighting level to be changed for a single bulb using the triac. His method was to attached a round, 2-inch section which allowed one end to screw in a socket, while the other allowed the bulb to screw in.

There are various types of dimmers today, including:

Rheostat – These were inefficient and dissipated a large load as heat.

Saltwater – Another type of Rheostat in earlier development, allowed liquid to move or be fixed to create variable contact.

Coil-rotation Transformer – Uses a fixed-position electromagnet coil for creating the variable voltage.

Autotransformer – Commonly known as Variac, this device more efficient than previous products due to the load being applied more independently.