I waffled about posting this in the Electronics/Lighting/Gadgets forum, but figured this forum might be more hip to what I have in mind. This would be in addition to my dyno taillight, to act as a back-up.
* PBP regulation says the taillight must be visible from at least 150 meters. I haven't done much testing of this, but it feels like a pretty low bar -- it's about the same distance as the inside of a 400 meter running track. Brighter would be fine, but not at the expense of:
* 24-32 hour running time
in solid mode. This is where most offerings I know of fall short -- rather than being dimmable, they use flashing modes to extend battery life. I rode through 4 nights in 2015, going to the 84-hour group would cut that down to 3 nights. Nights in France are about 10 hours long that time of year, and with better planning than last time, I'd sleep about two hours of each one. With a long enough runtime, I wouldn't have to fumble with batteries when I'm a zombie, a definite plus.
* Miminal weight. Without features like dimming, flashing or recharging, I'm thinking this kind of light shouldn't weigh much more than 2 AAAs, the LED, maybe a limiting resistor, the switch, and enough plastic to enclose it and attach it to the frame.
Does something like this exist? I'm a little concerned I may have to design and build it, since it's rather niche. Most people in the E/L/G forum (and probably everywhere else in the cycling world) seem to want retina-frying brightness and/or seizure-inducing flash modes.