Calipsoii's Project Lamplighter thread here
Cali created a very tiny, low-drain LED light to keep on his keychain as a 'find-me' with a different wow factor than a tritium vial. Rather than take his thread off topic, I'll post the build of a larger, more-powerful, but similarly-purposed device.
To develop a small, keychain-carry device with output visible in normal room lighting conditions as a super-find-me, also usable as a low-level light.
Higher current drain (whole milli-amps instead of nano-amps) requires either big primaries or rechargeable secondaries. My fabrication tools are limited, leading me to permanently-installed batteries with trickle charging. One hackish way to achieve this is with USB-powered trickle charging and a voltage-limiting Zener diode across the NiMHs. There are other ways, including having the battery case openable to charge as normal. But I've wanted to build a light like this, so I'm combining two projects.
Below is a 'rough draft.' I tend to do this for projects, using duct tape liberally.
The critter in my desk drawer. The inverted-cone thing makes an interesting beam pattern - a darker circle ahead like a minimag, but a good spread of light otherwise. I might dab a bit of hot glue and see if I can get a more spherical compromise than the torus of light output I get now.
The whole thing, on some duracells that came with some flashlight or another. I read 2.54v across the LED with my cheap multimeter, and around 2.5mA. I don't trust it at such low range.
In office-lighting conditions, it has a bit of 'extra' glow to it. In the dark, it stands out like a beacon. For my build, I plan:
USB micro socket with 160Ω resistor to charge batteries at a trickle
2 1/3AA NiMH cells with a zener diode (hackish overcharge protection) [14.5mm Dia x 16.7mm Height]
Maybe a high/low switch
Total size should be around 15mm diameter, 40mm long. So, about like a fat AAA, maybe.
This all assumes I find a case for it. It'll be tricky to design one from essentially found parts. Although I do have a drill now.