Friday, December 18, 2009

Lighting Dimmer

Dimmer is a device that is being used to adjust the light brightness. Dimmer works by increasing or decreasing the RMS voltage and hence the mean power to the lamp it is possible to vary the intensity of the output of the light. Variable-voltage devices are used for various purposes; dimmer is generally controlling resistive incandescent, halogen and compact fluorescent (CFL) lighting. To dim fluorescent, mercury vapor and other arc lighting, more specialized pulse-width modulation equipment will be needed for the dimmer.

The size of lighting dimmers varies from small units, used for domestic lighting, to high power units, used in large venue theatre or installation of architectural lighting installations. For the use of domestic lighting, small unit dimmers are generally directly controlled or the use of remote control systems is available. Modern professional dimmers, for architectural lighting or theatre installations, are generally controlled by a digital control system such as DALI or DMX. These protocols are often used in the conjunction with Ethernet.

The dimmer changes in intensity are often called fades in the professional lighting industry. Modern digital dimmer units have more adjustable speed in the control and built from silicon-controlled rectifiers (SCR) instead of potentiometers or other variable resistors because the SCR have higher efficiency. A variable resistor would dissipate the power by heat which has a lower efficiency compare to SCR dimmer, and SCR dimmer does not heat up.

Dimmers were used to be directly controlled through the manual manipulation of large dimmer panels. All of the power had to come through the location of the lighting control, this condition could be inconvenient and potentially more dangerous, especially with systems that had a large number of channels.

Analog remote control system or often called 0-10V lighting control systems became feasible when the thyristor dimmers were introduced. This dimmers were using smaller wire for the control system compared to the heavy power cables of the previous lighting systems. Every of the dimmer had its own control wires, this mean that a large number of wires leaving the location of the lighting control to each of the dimmer. Modern lighting systems are using a digital control protocol like DMX512, or DALI to control a large number of dimmers through a single cable only.

Dimmers can be controlled remotely by using various protocols. An analogue dimmers would usually need a separate wire for each of the dimming channel and carry a voltage between 0 and 10 V. Some of the analogue circuit also derives a control signal and the mains would supply the switches. More wires are needed between the lighting controller and the dimmers when more channels added.

DMX512, one of the digital protocols, have been one of the best choices since the late 80s. Modern dimmer designs are using microprocessors to convert the digital signal directly to a control signal for the switches. This method is giving closer control over the dimmer and giving a diagnostic feedback back to the lighting controller for monitoring.