How does DMX Actually work? This article was originally called “DMX Stage Lighting Systems – Get Them To Talk” but, apart from being a bit of a lame title, this actually misses the point of the serial DMX signal. Unlike modern networks, DMX lighting fixtures and their controller do not all “talk” to each other. When a DMX Lighting Control starts – everybody listens! Information about each “DMX Channel” (in the old days, a dimmer number) and it’s level (0 – 100%) is transmitted down the DMX “Universe” cable and each DMX stage lighting fixture, moving light or smoke machine listens for it’s own part of the signal stream and ignores everything else. The signal is then transmitted over and over in “packets”, giving a regularly updated stream for the rig to obey. The lighting console receives no information in this one-way street. In order for all the DMX stage lighting fixtures to have their own part of the signal stream, each one has it’s own “address” which is set on the fixture using buttons or switches. If a dimmer channel has a DMX address of 001 then it listens for the 001 part of the DMX signal then obeys the “channel level” value, 75% for instance. Once all intelligent lighting fixtures, dimmers and accessories are connected up and “addressed” the lighting desk can control each part of the rig individually using their own unique DMX address. The DMX Universe Back when we only controlled dimmers using DMX, life was simple. 1 DMX Channel = 1 Dimmer No. Then we started to use more complicated fixtures, moving lights and intelligent (?) lighting that needed more than 1 DMX channel per fixture. This means that fixtures are assigned a DMX “start address” which is the first channel in a sequential batch that the fixture listens to. If your fixture uses 6 DMX channels and you set it to a “start address” of 001 then it listens to channels 001,002,003,004,005 and 006. Your next free address for another fixture is then 007 because if you set it to 006 then the “channel overlap” would create a conflict of control. Setting fixtures to the same start address can be useful some circumstances and is a common method of DMX fault finding. With many DMX moving lights requiring the use of 20 or more channels, those 512 don’t look too many now, huh? A few moving lights, 100+ Dimmers, Strobes and a couple of smoke machines and you’ve run out of channels already! The solution to this problem is to connect and address some of your equipment on a second DMX “universe”, a different signal stream with even more cables. Many lighting control desks have more than one DMX output these days and the principles of fixture addresses and channel numbers apply to this, and subsequent, universes. The first DMX channel on a second universe is also 001 and each DMX universe is a totally separate stream, independent of each other.