The Leash Lantern was born of the need for reliable, durable and weatherproof illumination during dark walks in the cold Canadian winter.
For 5 months of the year, it gets dark around 4PM and stays dark until 9AM. It's very difficult as a driver to see pedestrians (particularly during snowfalls). I wear a lot of little coin-cell lights so that drivers don't run me over when walking the dog. The problem with coin cells is they really dislike cold and they're very expensive. I was tired of them dimming and dying mid-walk and then paying the high cost for replacements.
I designed the Leash Lantern to run on a single 1.5V AA battery. They're a good size to hang from a leash, they're readily available, and they have high energy capacity and tolerance for cold. In particular, the Energizer L91 lithium primary batteries can operate down to -40 and they boast almost 3500mAh of runtime (that's a lot!).
The circuit in the Leash Lantern is my own design - I call it the 15VP converter. I build each of them by hand in my basement. It has a tiny microcontroller that constantly measures battery voltage and LED output. It will automatically dim the output to keep you visible longer. It will notify you when the battery is getting low. It can be easily reprogrammed to change brightnesses and behaviours without ever opening the Lantern up.
The user interface is simple: tighten the tailcap for constant brightness. Loosen it to turn it off. And when you're coming up to a crosswalk, quickly turn it off and on for 30s of high output light for extra visibility.
The Leash Lantern body is made of solid bronze for corrosion resistance. The diffuser is a hard machineable plastic called Delrin. The whole thing is o-ring sealed so snow & rain won't get in. There are no switches to break, just a twist-action tailcap. It's a simple, reliable and durable assembly that has survived hundreds of drops in the 2 years I've been carrying my prototype.
And people like them! I've had cars pull up beside me in the street, roll down a window, and ask "Where'd you get that light?". Other dogwalkers have asked where they can get them. Cyclists have asked for one for their backpacks.
I've spent 2 years testing and refining this design and it's right where I like it. It's time to bring the Leash Lantern to leashes other than my own. Hang one on your leash, on your cycling bag, or from your belt loop. Clip it anywhere others can see it. And enjoy the increased visibility and safety during your own excursions out into the dark.