Addressable LED Strip: SPI, DMX and Pixel Limits
How addressable LED strip is controlled: SPI timing, WS2812B versus WS2815, DMX universes, pixel-per-output limits, refresh rate and flicker on camera.
HFY Applications Engineering · Published November 3, 2026 · 3 min read
Addressable strip is controlled by SPI, where each pixel receives its colour value in sequence over a single data line, or by DMX512 through an RS-485 bus to a converter. One SPI output typically drives 1,024 pixels at 800 Hz, and one DMX universe covers 170 RGB pixels, so a 1,200-pixel facade needs two SPI outputs or eight DMX universes.
Key points
- SPI is the protocol on the strip; DMX is the protocol from the console, joined by a converter.
- Pixel count per output, not total pixel count, is the number that sizes a controller.
- 24 V pixel strip exists to solve voltage drop, not to increase brightness.
- Refresh rate below 1 kHz produces banding on camera even when the eye sees nothing.
The signal chain
Console (DMX / Art-Net) → converter → SPI → pixel 1 → pixel 2 → … → pixel nEach pixel reads the first 24 bits of the data stream, consumes them, and forwards the remainder. This cascade is why a single broken pixel can take out everything after it — and why WS2815’s backup data line exists.
Protocol comparison
| Protocol | Wiring | Typical pixels per output | Refresh | Best for |
|---|---|---|---|---|
| WS2812B (5 V) | 1 data + power | 512–1,024 | 800 Hz | Short runs, furniture, wearables |
| WS2811 (12 V) | 1 data + power | 1,024 | 400–800 Hz | Longer runs with 3-LED groups |
| WS2815 (12 V) | 1 data + backup + power | 1,024+ | 1.1 kHz | Facades, reliability-critical installs |
| SPI 24 V | 1 data + power | 1,024 | 800 Hz–1.1 kHz | Runs above 10 m |
| DMX512 direct | RS-485 A/B | 170 RGB pixels per universe | 44 Hz | Stage fixtures, not strip |
DMX is a control-bus standard, not a strip protocol. A 2,000-pixel installation usually runs Art-Net from the console to a converter, then SPI on the strip.
Power, the real constraint
The controller does not supply pixel power. That comes from separate power supplies with injection points.
Current = pixels × 0.06 A (RGB at full white)| Pixels | Full-white current | Injection points at 24 V |
|---|---|---|
| 300 | 18 A | 1 |
| 600 | 36 A | 2 |
| 1,200 | 72 A | 3–4 |
| 2,000 | 120 A | 6–8 |
A 2,000-pixel facade at full white draws 120 A, which is 2.9 kW — and it will only draw that on a white test pattern, not on the show content. Size the supply for the test pattern, not the show, because the test pattern is what the commissioning engineer will run.
Refresh rate and camera flicker
The eye integrates light over about 20 ms; a camera at 1/1000 s shutter integrates over 1 ms. A strip refreshing at 400 Hz has a 2.5 ms frame, so a 1 ms exposure catches part of one frame and part of the next. That is visible as banding on video even though the installation looks stable in person.
For anything that will be filmed — retail windows, broadcast studios, media facades on camera — specify ≥ 1 kHz and verify with a phone camera at 1/1000 s before handover.
Addressing and layout
Mapped installations fail at the drawing, not the electronics. Confirm three things in writing before production:
- Start corner and direction of the first pixel.
- Serpentine path — which rows run left-to-right and which run right-to-left.
- Pixel index range per reel, labelled on the reel.
We label index ranges on every reel for mapped projects, which turns site wiring from guesswork into a lookup. The products and platform options are on the RGB and pixel strip page, and the supply sizing rules that keep the far end from shifting colour are in power supply sizing.
This article describes general manufacturing practice for machined and fabricated components. It is not a substitute for a drawing-specific engineering review — tolerances, material selection and process capability depend on the individual part.