Image Source: Hackaday.io
Ted Yapo had a small problem. As an amateur atronomer and astrophotographer, he needed a way to mark his expensive equipment so that he wouldn’t trip over it in the dark. Glow-in-the-dark materials were out because of they only glow for a short time, and glow sticks were also less than ideal because of their single-use nature. Tritium light sources would be perfect, barring the small details that they’re radioactive, expensive, and in the US only a few uses are allowed, most are prohibited by law.
So Yapo instead came up with an LED light that can run for not 20 hours, or even 20 days, but 20 years on a single CR2032 coin cell battery!
It does this with painstaking attention to the components use. By carefully regulating the current provided to the LED with PWM outputs from a PIC12LF1571 the amazing low-power performance is possible. It can be setup to either intermittently shine relatively brightly, or produce a constant glow if that’s what you prefer.
The device is for sale on Tindie via the Kontakt store. This seeler is not Yapo himself, but is part of the team on the Hackaday.io project. Since Yapo has open-sourced the design, this is entirely acceptable as he explicitly notes.
Yapo also has very good instructions on how to build one on the linked Hackaday.io page, though you likely won’t save any money sourcing things yourself unless you need to build quite a few of them.