LMT – Light choreography with 20,000 synchronized phones

A light choreography with 20,000 synchronized phones

Let’s be honest — yes, Coldplay’s glowing wristbands inspired us.

But the idea of thousands of battery-powered devices that would later need to be collected, stored, maintained, and babysat… felt overly complicated and not exactly eco-friendly.

So, we turned to something everyone already has in their pocket — their own phone.

At first, the idea seemed simple. But then came the big challenge: synchronization.

How do you get 20,000 phones to light up in perfect unison?

We explored a few options:

• Microphone-based sync (detecting a high-frequency audio code)

• Camera-based sync (triggering from a visual “cue image”)

• And syncing via global time.

For a long time, we clung to the microphone idea — like a sound-driven equalizer. But it didn’t deliver the control we needed. The result felt unpredictable and difficult to choreograph precisely.

So we switched to a solution based on global time and our own sync checkpoints.

This approach let us match lights to music and its dynamics with much greater precision — and without needing access to the phone’s camera, mic, or anything else intrusive.

But that introduced a new challenge: concerts are fluid. It’s rare that a song starts exactly at “21:07, sharp.”

Also, to know when to start, each device needs to ask our server: “Is it time now?”

If 20,000 phones do that simultaneously… it’s basically a DDoS attack. Unintentional — but still.

After many conversations with LMT’s network engineers and security teams, we realized this kind of load isn’t something well-documented globally. There’s no clear “safe limit” to rely on.

So we created a solution: devices were split into “batches,” each checking in at slightly different moments.

This drastically reduced the load, while still keeping everyone perfectly in sync.

Right before the show, we updated all devices with our master time cue — and the magic happened.

We also optimized the web app down to just 180 KB!

Multiplied by 20,000 users, that’s around 3.43 GB of data — not bad at all.

To make choreography easy, we also built a custom light control panel, allowing us to mix effects like solid, strobe, gradient, and random. It gave us near-millisecond control over the show’s rhythm and feel.

Huge thanks to the creative father of the concert, Papa Chi, to the mastermind behind the code, Rihards Grāvis (who, by the way, also has deep roots in the mushroom business — https://spora.lv), and to the LMT marketing, security, and engineering teams for making this innovation possible!