Basics 3. Fixture address: how a command finds the right light

All the fixtures hang on the same cable and receive the same stream of 512 numbers. So why does the first one turn red and the second one blue? Because every fixture has an address: the place in that stream where it starts reading «its own» part. The address is the single most common cause of odd behaviour on site — and at the same time one of the simplest things to understand.

The address is the number of the first channel that belongs to the fixture

A fixture occupies several consecutive channels — as many as it has abilities. The address (also called the start address, the DMX address, or simply «the address») tells the fixture where its block begins.

Give a 6-channel fixture the address 1 and it takes channels 1, 2, 3, 4, 5, 6. Give it address 7 and it takes 7–12. Everything else in the line it ignores, as if those numbers did not exist.

Fig. 1 — A line of 512 channels and the fixture blocks: the address is the number of the first cell in a block

An analogy: a DMX line is a long street with houses numbered 1, 2, 3… 512. A fixture is a family occupying several houses in a row. The address is the number of the first house. The postman (the desk) simply drops a letter at every house in order; working out which letter is for whom is the residents’ business.

Working out addresses: one line of arithmetic

There is a single rule: the address of the next fixture = the address of the previous one + its number of channels.

Take four identical 6-channel fixtures:

Fixture	Address	Channels used
Fixture 1	1	1–6
Fixture 2	7	7–12
Fixture 3	13	13–18
Fixture 4	19	19–24

The fixtures can be different — the arithmetic does not change. Add a 14-channel moving head: the next free address after the four fixtures is 25, so the head takes 25–38 and the fixture after it starts at 39.

⚠️ Careful: a fixture does not know how many channels the software thinks it has. It simply reads, from its address, as many channels as its current mode provides for. So two things have to agree: the address and the mode (more on the mode below).

What happens when addresses overlap

Suppose you slipped and gave the second fixture address 4 instead of 7. Now channels 4, 5 and 6 are read by both fixtures: the first treats them as its green and blue, the second as its intensity and red.

The result in the room looks like witchcraft: you push the intensity of the second fixture and the colour of the first one changes. You set the first to blue and the second flashes for no reason. Nothing is broken — two households are simply getting the same letters and each reads them their own way.

💡 Tip: if fixtures seem to «affect each other», the addresses have almost certainly overlapped. Check the arithmetic: each fixture’s block must start where the previous one ended.

Now the same trick on purpose. Give two identical fixtures the same address and they become perfect twins: always the same colour, always the same intensity, controlled as one. This is a legitimate and very handy move when fixtures work in pairs (symmetrically left and right of the stage, say) and you do not need to control them separately. The downside is obvious: you cannot split them again without changing the address.

Setting the address on the fixture itself

The address has to be set in two places: in the software (where you simply type a number) and on the fixture. The software cannot set the address remotely — the fixture never asks it.

Method 1. A display with buttons. The modern option: a small screen and three or four buttons on the back or side panel (usually MENU, UP, DOWN, ENTER). You go into a menu item called something like Addr, DMX Address, A001 or d001 and dial in the number.

💡 Tip: the number is often shown with a letter — A012, d012, CH12. Read the digits; the letter only means «address». Also, on many fixtures the display goes dark after a minute — press any button to wake it.

Method 2. DIP switches. A relic of the past — rare nowadays, mostly on older and very basic fixtures: a block of 9–10 tiny switches. The address is the sum of the «weights» of the switches that are up. It is binary counting, but there is nothing to fear: a table is all you need.

Fig. 2 — DIP switches: the address is the sum of the weights of the raised switches

Switch	1	2	3	4	5	6	7	8	9
Weight	1	2	4	8	16	32	64	128	256

To get the address you need, raise the switches whose weights add up to that number. Examples:

address 1 → only switch 1 is up;
address 13 → switches 1 + 3 + 4 (1 + 4 + 8 = 13);
address 100 → switches 3 + 6 + 7 (4 + 32 + 64 = 100);
address 256 → only switch 9.

You do not have to do the sums in your head: the internet is full of «DMX DIP switch calculators», and the fixture manual usually has a ready-made table for every address.

⚠️ On the vast majority of fixtures the address equals the sum of the raised switches, but there are models where it is calculated as «sum + 1». The tenth switch (if there is one) has nothing to do with the address — it usually selects the operating mode: DMX / auto program / sound active / master-slave. Always check against the table in the manual for your specific model.

💡 Tip: a fixture in «auto» or «sound» mode will flash away on its own and ignore the desk entirely. If one fixture in the row is living its own life, first make sure it is in DMX mode at all.

Channel mode: the address is only half the job

Most modern fixtures have several operating modes that differ in channel count. The same fixture may run as 4-channel (intensity plus R, G, B — that is, red, green and blue), 6-channel (adding strobe and auto programs) or 9-channel (adding colour macros and speed). The mode is chosen in the same fixture menu and appears in the manual as Channel Mode or DMX Mode, for example 4CH / 6CH / 9CH.

The mode on the fixture must match the profile in the software. If the software thinks the fixture is 6-channel while it is actually running 4-channel, every command past the fourth channel lands in the wrong place: you move the strobe and the fixture changes colour, you move the colour and it goes dark. The symptom is very distinctive: fixtures respond, but with a different parameter than the one you are touching — everything is «shifted».

Fig. 3 — In the software each fixture shows both its address and its mode (channel count)

That is exactly why the same model appears several times in profile libraries — «PAR 180 COB 3in1 (7 ch.)», «Spica 250M (16bit, 16 ch.)», «Spica 250M (8bit, 14 ch.)». These are not duplicates but different modes of one fixture: pick the one set in your unit’s menu and suited to the job at hand.

Three habits that save hours on site

Address with room to spare. You do not have to pack fixtures tight (1, 7, 13, 19). Round addresses with a gap are handy: 1, 11, 21, 31 — then a fixture with more channels drops into a ready-made hole and you do not have to re-address the whole line.
Write down the address map. A simple «fixture — address — mode» table on paper or in your phone. A month from now you will not remember what was set on the far head under the ceiling.
Label the fixtures. A strip of masking tape with the address on the housing — a trick every rental company uses. Especially useful when the fixtures are rigged high up.

📍 How this looks in SvetoMaster: addresses and modes live in the Patch section — a table listing all your fixtures: name, type, universe, address and mode (14CH, for instance). The program assigns non-overlapping addresses itself when you add fixtures, but you can type in any address by hand if the hardware is already set and you would rather not change it. Overlaps are highlighted, so the classic «two fixtures in the same place» mistake is visible at once.

Key points

The address is the number of the fixture’s first channel in the line; from there it reads as many channels as its current mode has.
The address of the next fixture = the previous address + its channel count.
Overlapping addresses make fixtures affect each other; the same address on purpose makes them twins.
The address is set on the fixture itself: with display buttons or DIP switches (the sum of weights).
The fixture’s channel mode must match the profile in the software, otherwise everything is shifted.
A separate switch or menu item can put a fixture into «auto» or «sound» mode — and then it ignores the desk completely.

Coming next: we can address fixtures now, but we still do not know what each of their channels means. The next lesson is about the fixture profile and the channel table: how to read a manual, what all those Dimmer, Shutter, Gobo and Prism entries mean, and what to do when your fixture is in no library at all.

Next lessonFixture profile and channel table: reading the manual