Lumen

Move a file between two devices on light alone.

One HTML file. No install, no account, no server, no pairing — and no network. The sender turns your file into a stream of QR codes; the receiver's camera reads them back. Both devices can be in airplane mode.

Use it

https://itstejaswi.github.io/lumen/

Open that on both devices. On iPhone, tap Share ▸ Add to Home Screen — it then launches like a native app and never needs the network again.

What this page does and does not do

This site exists only to deliver the app. Once the page has loaded, it makes no further requests: no analytics, no telemetry, no CDN, no fonts, no service worker. Everything — QR encoder, QR decoder, fountain code, compression — is inside the single HTML file.

Your files are never uploaded. They never touch this host, GitHub, or any network. The transfer happens between two screens and two cameras. The host can see that someone fetched the app, and nothing else.

You can verify this: load the page, then kill your connection. Everything still works.

Why it must be https

Browsers only grant camera access on a secure origin. A plain http://192.168.x.x address will load Lumen but the receiver's camera will be blocked. https (or a file:// local copy, or localhost) is required.

Why iPhones need a link at all

iOS sandboxes every app, so nothing can hand a local .html file to Safari — the share sheet only ever offers Notes, Mail and similar. Tapping the file in Files shows a preview, which cannot run scripts. A link is the only route in, and the easiest way to open one is to point the iPhone Camera at a QR code of it: the Camera app opens links in Safari directly.

Running it yourself

Nothing here is required. The file works from disk on Android, Windows, macOS and Linux — just open it. To serve it locally:

node serve.js 8000            # http://127.0.0.1:8000  (localhost is secure)
node serve-https.js 8443      # https on your LAN, for phones

How it works

• Fountain code (LT) — the sender emits an endless stream of random block combinations, so the receiver never has to catch a specific frame. Drop one and it repairs itself; no back-channel is needed.
• Base45 (RFC 9285) packs bytes into the QR alphanumeric set efficiently.
• CRC32 on the whole file, verified after reassembly.
• Built-in QR encoder and decoder — Safari has no BarcodeDetector, so the decoder is written from scratch and used on every iPhone.

Credits

QR Code® is a registered trademark of DENSO WAVE. LT codes, M. Luby. Base45, RFC 9285.

Vibe coded by Tejaswi · Made with ❤️ and Microsoft Scout