DMX

DMX is the serial protocol a lighting console uses to tell fixtures what to do. The current standard is ANSI E1.11, and the protocol’s proper name is DMX512-A; the trade says DMX and means this.

One data link carries five hundred and twelve channels, and that set is called a universe. The number is a timing decision rather than an arbitrary one: a full packet of five hundred and twelve channels refreshes about forty-four times a second, and doubling the channel count would have halved that and made fades visibly step.

How far a universe goes depends entirely on what is on it. A single-channel dimmer or a three-channel colour wash costs almost nothing; a multi-parameter moving head takes twenty to thirty consecutive addresses, so a universe holds around twenty of them. Channel count per fixture, not fixture count, is what fills a universe — and most fixtures offer modes that trade resolution for channels.

Two practical rules account for most DMX faults on site. The last device on a run needs a one hundred and twenty ohm terminator, because without one the signal reflects back down the cable and produces flicker and random behaviour that look like a fixture fault. And a run supports thirty-two devices before it needs a powered splitter, which is an electrical limit of the underlying wiring rather than anything to do with lighting.

Event lighting — owned inventory, our own crew, and a site survey before anything is specified.

• Lighting console The desk that holds the patch, the looks and the running order — and the reason a show can be rebuilt in ten minutes when a speaker is moved up the programme.
• Moving head A fixture that pans, tilts and changes colour, beam and pattern on command — bought in three distinct flavours that are routinely confused when a rig is specified.
• PAR fixture The simplest instrument in the rig — an oval pool of hard, bright light with its beam spread built into the lamp rather than adjusted at the fixture.