Understanding DMX
An introduction to DMX512 for lighting control, covering channels, universes, fixture addressing, and how cabling and protocols connect them.
What is DMX?
DMX512 (Digital Multiplex 512) is the standard protocol for controlling stage lighting. It dates from 1986, and theatrical, concert, and architectural lighting use it worldwide.
Key concepts
Channels
- A DMX universe has 512 channels.
- Each channel sends a value from 0 to 255.
- Channels control specific functions (dimmer, color, position).
Fixtures
Each fixture uses one or more channels:
- Simple dimmer: 1 channel.
- RGB LED: 3 channels (Red, Green, Blue).
- Moving head: 8-40+ channels.
Addressing
Each fixture gets a start address (1-512):
- A fixture at address 1 with 4 channels uses channels 1-4.
- The next fixture can start at address 5.
Each channel should belong to only one fixture.
Universes
One universe equals 512 channels
Larger shows use more than one universe:
- Universe 1: channels 1-512.
- Universe 2: channels 513-1024 (conceptually).
- Each universe is independent.
Multiple universes
You can carry multiple universes over:
- Multiple DMX cables.
- Art-Net over Ethernet (up to 32,768 universes).
- sACN (Streaming ACN, up to 63,999 universes).
Channel values
The 0-255 range
| Value | Meaning |
|---|---|
| 0 | Minimum (off, closed, etc.) |
| 127/128 | Middle/default |
| 255 | Maximum (full, open, etc.) |
Common uses
| Channel Type | 0 | 255 |
|---|---|---|
| Dimmer | Off | Full |
| Color (R/G/B) | None | Full saturation |
| Pan/Tilt | Min position | Max position |
| Strobe | Off/Open | Fast strobe |
| Gobo | Open | Various gobos |
Fixture modes
Many fixtures have multiple DMX modes.
Example: LED Par
3-channel mode:
- Ch 1: Red
- Ch 2: Green
- Ch 3: Blue
7-channel mode:
- Ch 1: Dimmer
- Ch 2: Red
- Ch 3: Green
- Ch 4: Blue
- Ch 5: Strobe
- Ch 6: Color macros
- Ch 7: Mode select
The physical mode setting on the fixture must match the mode in your software.
Address planning
Simple example
| Fixture | Type | Channels | Address |
|---|---|---|---|
| LED Par 1 | 4ch | 4 | 1 |
| LED Par 2 | 4ch | 4 | 5 |
| LED Par 3 | 4ch | 4 | 9 |
| Moving Head | 16ch | 16 | 13 |
Best practices
- Leave gaps in the address plan so you can add fixtures later.
- Group fixtures of the same type together.
- Keep a written record of every patch.
- Start fixture addresses on round numbers (1, 10, 20, 50, 100).
Physical connections
DMX cables
- 5-pin XLR (professional standard).
- 3-pin XLR (common but not to spec).
- Never use audio cables for DMX.
Daisy chain
Connect fixtures in series:
Controller → Fixture 1 → Fixture 2 → Fixture 3 → TerminatorTermination
At the end of long runs, add a 120Ω terminator to prevent signal reflection.
Cable limits
- Maximum 300m (1000ft) per run.
- Maximum 32 devices per run.
- Use splitters for longer or larger installations.
Art-Net
Art-Net carries DMX over Ethernet.
Advantages
- Multiple universes over one cable.
- Switches and fiber links extend the network beyond the 100m limit of one Ethernet cable.
- Runs on standard network equipment.
Addressing
Art-Net uses Net/Subnet/Universe:
- Net: 0-127.
- Subnet: 0-15.
- Universe: 0-15.
For a simple setup, use Net 0, Subnet 0, and Universe 0, 1, 2, and so on.
Troubleshooting
No output
- Check cable connections.
- Verify that the fixture is in DMX mode.
- Confirm that the address matches.
- Check for address conflicts.
Flickering
- Check for cable damage.
- Add or verify termination.
- Reduce cable length.
- Check for electrical interference.
Wrong behavior
- Verify that the fixture mode matches the patch.
- Check channel assignments.
- Confirm value ranges.