The signal that carries commands to the luminaires is the invisible but most critical part of a facade lighting installation. We explain the signal types, distance rules and the causes of signal problems.
A facade lighting installation has two separate lines: the power line that carries energy to the luminaire and the data line that tells the luminaire what to do. Most problems, such as lights flickering, switching to random colors or the luminaires at the end of the line not responding at all, come from the second, that is, from the control signal.
A control signal is the digital data that travels from the control device to the luminaires and carries the information “this luminaire should glow in this color, at this brightness”. This data is carried in different ways depending on the type of luminaire, the protocol used and the cable distance.
Data is carried over a single wire as a voltage level relative to ground. It is simple and economical, but susceptible to electrical noise and degrades as the cable gets longer. The signal used by SPI pixel chips is of this type.
Data is carried as the voltage difference between two wires. Because noise picked up on both wires at the same time cancels out, it is reliable over long distances. DMX512 uses this structure.
Art-Net and sACN (ANSI E1.31) carry many DMX universes over a standard Ethernet network. Many universes can be carried on a single network cable; long distances are covered with network switches and, when necessary, fiber optic links. On large pixel-controlled facades, this is usually the backbone of the system.
For single-color luminaires that do not change color and only have their light level adjusted, dimming methods such as DALI, 1-10V or PWM are used. These are for managing the light level, not for pixel animation.
| Signal | Typical cable | Practical note on distance |
|---|---|---|
| SPI (TTL) | Short data cable | Should not exceed a few meters between the controller and the first pixel; use an amplifier if needed |
| DMX512 (RS-485) | 120 Ω twisted pair, shielded | Recommended up to 300 meters and 32 devices per segment |
| Art-Net / sACN | Cat5e / Cat6 network cable | Max. 100 meters between two network devices on copper cable; fiber for longer runs |
Whatever signal is used, not running the data cable in parallel with power cables in the same conduit over long distances, connecting the shield correctly on shielded cables and protecting the connection points against water and moisture directly affect signal quality.
| Symptom | Possible cause |
|---|---|
| Lights flicker or random colors appear | No termination resistor on the DMX line, unsuitable cable, or the line has been branched |
| Luminaires at the end of the line do not respond | The line is too long or too many devices are connected; an amplifier or splitter is needed |
| Dark after a certain pixel | A faulty chip or broken connection in the SPI chain |
| Animation stutters | Too many pixels connected to the controller output; the refresh rate has dropped |
| Colors in the wrong order | Wrong color order (RGB/GRB) or chip type selected in the controller |
Always start troubleshooting from the beginning: first check the output of the control device, then the first luminaire, then the line section by section. The point where the fault begins often shows the source of the problem.
Colors fading toward the end of the line or white shifting to yellow is usually a power problem, not a data problem. On long low-voltage (e.g. 24 V) lines, voltage drop along the cable reduces the voltage reaching the luminaire. The solution is to feed power at different points along the line, increase the cable cross-section or choose higher-voltage systems such as 48 V.
In our products, the control infrastructure is determined by the light type. Our single-color (MC) in-ground luminaires can be dimmed via PWM, 1-10V and DALI; the dynamic white, RGB and RGBW versions run on DMX512. In our pixel-controlled products, SPI is standard and DMX512 optional, and the power supply is 24 V DC as standard, 48 V DC optional.
We can plan together which control and power structure suits your project, and where the controllers and power supplies will be placed.
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