The circuit is the plug into which the fixture is plugged. The dimmer refers to the individual dimmer in the dimmer rack. A DMX512 cable runs back to the light board for control. The channel is the assigned number within the light board for organization when designing. This entire process is called the “patch.”

Some theaters have a one-to-one patch. This system is simply a straight line from circuit to channel that all match in number. Circuit 1 to patched to dimmer 1 which is patched to channel 1. This system can be useful when there are a small number of circuits available. Knowing immediately which fixture is having a problem without looking at paperwork can be very nice, but the ease of use depends on the light board.

A patch panel could be installed in a theater, but is becoming rare. This system is a physical patch from one panel to another which links the circuits to each dimmer at the discretion of the designer instead of being hard wired. Dimmers have a wattage limit to them and these need to be considered when patching and cabling fixtures. The wattages of the lamps can be added together, but must not exceed the rating of the dimmer. The dimmer will trip, like a circuit breaker at home.

Often the lighting designer will choose separate channels to fit each individual production to quickly write submasters or cues. A submaster is a way to group channels together. These are sometimes also called scenes because the intensities are recorded to the submaster fader. A cue is recorded into the board, much like a submaster, but can be recalled for greater accuracy. The cues would be triggered by a “go” button. The fade times are controlled via the computer. Not all light boards have this option, but it is becoming far more common even in poorly funded theaters.

The DMX512 control boards have a limited number of channels. There are two types of channels that the designer and board operator need to be concerned with. There are control channels and intensity channels. Control channels refer to how many lines of DMX512 are available to the board. Each individual line has 512 control channels. The intensity channels vary based on the manufacturer. The intensity channel refers to the assigned channel from the dimmer. These are limited based on the board, but upgrades can often be purchased up to give you greater options.

LED PARs are one of the new instruments that do not require the dimmer system. The power supply needs to be a continuous source at full power. This is traditionally achieved through the wall power outlets. DMX512 cables then run directly to the light board. The programmable control channel on the fixture itself refers to the starting DMX address. Through the patch screen on the light board the DMX channel on the fixture is used as if it were the dimmer number. Each DMX512 has a numbered slot on the back of the light board. The dimmer rack is usually entered into DMX 1. This makes these control channels 1-512. The LED PARs would then be inserted into DMX 2. Since we can’t use the same numbers the control channels are 513-1024. This continues for up to four DMX universes.

The LEDs may take multiple control and intensity channels. This is where the designer and programmer need to be careful. Patching dimmers together on one channel may become necessary to fit all the desired instruments into the show. Since channels are imaginary numbers, they have no physical limitations. A dimmer has a wattage limit, but every dimmer could be controlled by a single channel. Again, this would limit your options when controlling the fixtures and is rarely desirable.

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