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| The LightInk has a clearly visible solar panel |
While solar-powered smartwatches remain a niche corner of the wearable tech market, they’re not entirely unheard of. Most consumers immediately think of Garmin’s Fenix series—like the Garmin Fenix 8, which we reviewed at launch—where the solar panel is almost invisibly integrated into the display. But a new player has emerged from an unexpected place: the DIY scene. And it’s taking a radically different approach.
Meet LightInk, an open-source, self-assembled smartwatch that puts its solar panel front and center—literally. Unlike mainstream hybrids that try to hide the photovoltaic cells, LightInk proudly separates its solar panel from the display, making energy harvesting a visible, almost design-forward feature. But don’t look for it on store shelves. This watch isn’t sold commercially; you have to build it yourself.
The DIY Revolution: Why Build Your Own Smartwatch?
The LightInk project, hosted on GitHub, is aimed at makers, tinkerers, and anyone tired of charging their wrist every night. The core philosophy is simple: maximize battery life by stripping away power-hungry components and leaning hard into solar efficiency. According to the project’s documentation, the watch can run for up to 10 months on a tiny 100mAh battery when exposed to regular sunlight.
For those interested in diving into the build, the complete guide, schematics, and firmware are available on GitHub here.
But before you grab your soldering iron, know what you’re getting into. Building a LightInk requires access to a few non-trivial resources: you’ll need to order a custom PCB from a service like JLCPCB or PCBWay, have a 3D printer (or access to one) for the case, and be comfortable soldering small components. It’s not a beginner project, but the detailed documentation makes it achievable for intermediate makers.
No Accelerometer, No Companion App – But LoRa and GPS
LightInk deliberately omits several features you’d expect from a modern smartwatch. There’s no accelerometer—the project’s creator notes that it would simply consume too much power. Instead, the watch focuses on what matters for ultra-long endurance: a low-power E Ink display that remains perfectly readable under direct sunlight, a backlight for nighttime use, a tiny speaker, and LoRa wireless connectivity for long-range, low-bandwidth communication.
GPS is also onboard, though its inclusion raises an interesting trade-off. Without a companion app (none exists yet), the watch sits in a curious middle ground—it’s more than a traditional wristwatch but less than a full-fledged smartwatch. You can track your location, view the time and notifications (via LoRa), but you won’t be syncing data to your phone any time soon unless someone builds that app.
How It Compares to Garmin Fenix and Other Solar Wearables
Garmin’s Fenix line remains the gold standard for commercial solar-assisted smartwatches. On the Fenix 8, the solar ring adds a few extra days or weeks of battery life depending on usage, but you’re still looking at a device that costs $800+ and needs charging every few weeks under ideal conditions. LightInk, by contrast, targets months of autonomy but asks you to give up real-time heart rate, step counting, a polished OS, and any semblance of retail support.
Where Garmin hides its solar cells beneath the glass, LightInk’s separate panel is a deliberate design choice. It’s not as elegant, but it’s arguably more efficient—and certainly more hacker-friendly. The E Ink display is another divergence: most smartwatches use power-hungry OLED or LCD panels, while E Ink only consumes energy when the image changes. That’s why a 100mAh battery can last nearly a year with occasional solar top-ups.
Is LightInk Practical? That Depends on Your Definition
Let’s be real: most people will never build a LightInk. It’s not waterproof to any serious depth (the 3D-printed case offers basic splash resistance), it lacks any health sensors, and the lack of a companion app means you can’t even offload GPS tracks without some custom scripting. But for a niche audience—off-grid enthusiasts, hackers, and minimalists who despise daily charging—this watch is a breath of fresh air.
The project is still evolving. The GitHub repository shows active development, and the creator has hinted at future features like a basic phone companion over LoRa or BLE. But for now, LightInk is proof that you don’t need a billion-dollar R&D budget to rethink what a smartwatch can be. Sometimes, the most interesting ideas come from a soldering bench, not a corporate lab.
Specs at a Glance
- Battery: 100mAh Li-ion, recharged via visible solar panel
- Battery life: Up to 10 months (with regular sun exposure)
- Display: E Ink with backlight
- Connectivity: LoRa, GPS (no cellular or Bluetooth yet)
- Other: Speaker, DIY PCB, 3D-printed case
- Missing: Accelerometer, heart rate monitor, companion app
Where to Start
If this sounds like your kind of project, head over to the LightInk GitHub page.
You’ll find a bill of materials, step-by-step assembly instructions, PCB Gerber files, and STL models for 3D printing. Expect to spend a few evenings soldering and calibrating—but the reward is a solar-powered smartwatch that laughs at your old Apple Watch’s daily charging routine.
In a world of disposable wearables, LightInk stands out as something rare: a truly repairable, modifiable, and long-lasting device that you can call your own. Just don’t expect to buy it on Amazon.