Digital protocol controlling individual lights via addressable channels — wireless, daisy-chained, industry standard. One DMX cable replaces dozens of power lines.
You have 40 lights on your set — previously, you would have needed a separate power cable and dimmer for each. With DMX, you connect them all to a single cable and control each fixture individually from the console. This is the principle: a digital protocol that sends commands serially over twisted-pair cables and can address each dimmer or intelligent moving light.
The standard uses five-pin XLR connectors (in practice, three-pin is also used, but five-pin is more robust). The first DMX fixture gets address 1, the second address 2 — up to 512 channels per line. Each channel controls a function: intensity, color, pan, tilt, focal length. On the lighting console fader, you tell channel 7 to go to 100% — the fixture with address 7 receives the information and reacts immediately. Latency is practically zero, which is crucial for live editing or fast transitions. You program scenes, save them, and run them in the cue sheet. This is independent of the power supply — DMX is a pure data signal.
In practice: Every DoP needs to understand DMX because the gaffer works with it and you need to implement lighting setups live. During test setups, you ask: Who is setting up the addressing? Who is at the console? The most common problems are damaged cables (loose connections), missing terminators at the end of the chain, or address conflicts when two fixtures are assigned the same number. A DMX tester costs 50 Euros and can save you hours of troubleshooting.
Modern consoles also have RDM (Remote Device Management) — this allows you to query the addressed fixtures to find out what they are and what functions they can perform. This is no longer pure DMX, but the standard has long been hybrid. Wireless DMX via W-DMX or similar uses RF transmitters instead of cables — practical for quick setups, but susceptible to interference on densely equipped sets. Wired remains the reliable option.
For you as a DoP: Understand that lighting configuration is not an isolated setup. DMX ties you to the gaffer and the crew. For changes, for location moves — factor in time for addressing and testing. Some DPs work with their own DMX knowledge, others rely on the gaffer. Both work if communication is clear.