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A stage fixture's power-on state is what it does when power comes back: it runs a short self-test, then either follows DMX or, with no signal, holds the last look, goes dark, or runs a built-in program, depending on its mode and menu settings. Choose those settings for each fixture before the event, so a power cut or a lost DMX cable leaves the stage in a state you planned.
What happens when a fixture powers up
Most DMX stage fixtures go through the same sequence when power is applied:
- Boot. The display lights up and the fixture loads its stored settings: DMX address, channel mode, operating mode, and any menu options, such as a flipped LCD screen. These are kept in memory, so a normal power cut does not erase them.
- Reset or homing. Moving heads swing through pan and tilt to find their home positions and reset color and gobo wheels. This usually takes several seconds and can take longer on larger fixtures. Expect beams to sweep across the room during this step unless the fixture keeps the light off while homing.
- Mode decision. The fixture checks its operating mode. In DMX mode it follows the controller. In auto, sound, or slave mode it runs its built-in programs, whether a controller is connected or not.
- Signal check. In DMX mode with no valid signal, the fixture falls back to its no-signal behavior.
Most surprises after a power cut come from step 3 or 4: a fixture that was quietly left in sound mode, or one whose no-signal setting runs a demo program.
The no-signal setting: hold, blackout, or auto
Many fixtures let you choose what happens when DMX disappears. The menu item goes by names such as "No DMX," "Signal Loss," "DMX Fail," or "Hold," and the choices usually include some of these:
| Setting | What the fixture does | Good for | Watch out for |
|---|---|---|---|
| Hold last | Keeps the last DMX values it received | Front light, stage washes, anything the stage cannot do without | A strobe, fast chase, or extreme position will also be held |
| Blackout | Turns the light output off | Moving heads, beams, strobes, lasers, effects | The stage goes dark if the controller drops out |
| Auto or sound program | Runs a built-in show | Parties with no operator | Random colors and movement in the middle of a speech or a first dance |
Not every fixture has this menu. Some budget fixtures always hold, some always go dark, and some switch to an auto program. The manual may not say, so test it: run the fixture from DMX, then pull the DMX cable at the controller and watch what it does.
For a typical small stage, a sensible default is hold for the wash PARs that light people, and blackout for moving heads, beams, and lasers. If the controller fails, the speaker stays lit and nothing in the air starts swinging around.
Effect machines need extra care. Fog and cold spark machines should stop their output when control is lost. If a machine's menu offers a setting for this, choose the one that stops output, and test it with the machine pointed somewhere safe. If it has no such setting, never leave a fire or fog channel up in a scene that could end up held. Cold spark machines spray hot metal particles; keep the safety distance in the manual even during testing.
The controller side
The fixtures only see what the controller sends, and controllers do not all start up the same way:
- Hardware scene controllers may start with all channels at zero, with the last scene, or with blackout engaged. Check yours by switching it off and on with the rig connected.
- Laptop software with a USB-DMX interface stops sending when the laptop sleeps, crashes, or closes the program. Some interfaces keep repeating the last frame; others stop. Turn off sleep and screen-saver settings before the show.
- Art-Net or sACN nodes often have their own loss-of-signal setting: hold the last frame or stop output. Set it to match what you chose on the fixtures.
- Wireless DMX receivers may hold or drop the signal when they lose the transmitter. Battery-powered PARs keep running through a mains cut, but if the transmitter is on mains power, they fall back to their own no-signal behavior.
A small UPS (uninterruptible power supply) for the controller, laptop, and node keeps DMX flowing through brief power dips. It does not need to run the fixtures. It just keeps the control side alive so the fixtures never lose signal.
Recovering from a power cut mid-show
- Put the controller in blackout if it is still running, so fixtures come back to a known dark state instead of the last cue.
- Find out why power dropped. If a breaker tripped, reduce the load on that circuit before resetting it. If the venue lost power, wait for the venue to confirm it is stable.
- Restore power in groups, a few seconds apart. Moving heads draw extra current while they start up and home, and a whole circuit starting at once can trip the breaker again.
- Wait for every moving head to finish homing.
- Check that the controller is outputting and the right scene or show file is loaded.
- Release blackout into a simple, safe look, such as a stage wash, then return to the running order.
The stage lighting rig is not the venue's emergency lighting. Exit signs and emergency lights are separate systems with their own backup power, and the venue is responsible for them. Do not cover them or rely on your rig to light the exits.
Pre-show test for power-on states
Ten minutes before doors open is too late to discover a fixture's no-signal behavior. Run this test during setup:
- Bring up a normal look from the controller.
- Unplug the DMX cable at the controller. Note what each fixture does.
- Plug it back in. Confirm every fixture returns to DMX control.
- Switch off one power chain and switch it back on. Watch homing, then confirm the fixtures pick up DMX again.
- Switch the controller off and on. Note how it starts.
- Write the results on your patch sheet, next to each fixture's address and mode.
If a fixture's behavior is unsafe for your event and the menu cannot change it, run it from a separate DMX line you can unplug, or leave it out of the show.
FAQ
Why do my lights start a program by themselves when I power them up?
They are set to auto, sound, or slave mode, or their no-signal setting runs a built-in program. Switch them to DMX mode, connect the controller, and check the no-signal option in the menu.
Should fixtures hold the last look or go dark when DMX is lost?
Hold for the lights that keep people visible, such as front wash PARs. Blackout for moving heads, beams, strobes, lasers, and effect machines, so nothing flashes or moves without an operator.
Why did my moving heads swing around when the power came back?
That is the homing routine. Moving heads find their pan and tilt limits each time they power up. It is normal, but it is a good reason to bring power back with the controller in blackout and before the audience is looking.
Will a fixture forget its DMX address after a power cut?
Normally no. Address and mode are stored in the fixture's memory. If a fixture keeps losing its settings after power cycles, contact the seller's support, because the fixture needs service.
