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Electronic Theatre Controls Inc

Low Wattage Dimming

SCR, or forward phase dimmers often have a requirement for a MINIMUM load to be drawn from them in order to dim correctly. The minimum load varies depending on the dimmer type, but is typically 60-100W. Some modern loads like LED lighting may be significantly less than this, so ETC has a variety of dimmer modules described below to help in these cases.

There are a few different categories of low wattage loads that commonly require dimming :

Low Voltage / Dichroic Lamps


Low Voltage, Dichroic Lamps.jpgFor smaller light sources there are many advantages to using a lower voltage - a lower voltage allows you to use a thicker, shorter filament which reduces the fragility and increases the lifespan of the lamp Dichroic sources like the lamp shown on the left are typically run on a voltage of 12V. This is provided by a transformer. There are two classes of transformer in general use, either Electronic or Magnetic transformers.

The ability of all types of transformer to be dimmed vary, and it is important to check the ability of a transformer to dim before it is installed.

Magnetic Transformers

Magnetic Transformers generally dim well, provided that the load on the circuit exceeds the minimum load on the dimmer.

Electronic Transformers

Electronic transformers are increasingly common as they are lighter weight, use less copper and are becoming cheaper than magnetics. However, not all electronic transformers are dimmable. It is very important before installation to check that the transformer you are using is described as forward phase dimmable by the manufacturer before you try and dim it. Reverse phase dimmable transformers can be dimmed by one of our reverse phase dimmers, or sinewave dimmers.

LED Lamps

LED lamps.jpgLED Lamps generally use multiple LEDs packaged together to provide a light source. They are either operated via a low voltage source (12 or 24V similar to Dichroic lamps), directly from 110/230V mains, or via a dedicated control system.

Dimming LEDs is very different to dimming tungsten sources, in that the LED will maintain a fairly constant brightness until a cutoff threshold is reached and it will go out.

Systems with dedicated controllers can take an input control signal like DMX or DALI and convert it to a dimmed output to control LEDs. This is undoubtedly the best method of dimming LEDs and will produce the highest quality dimming.

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