'Biking in a Big City' has put up a great post comparing AAA taillights. I have comments below that post, but I'll expend on them here. Note that all good lights now are LED, since they are bright and use little power; HID, incandescent and halogen are finished.
There are several questions that want answering about your bike lighting needs:
- urban or rural riding (city needs brighter)?
- how much night-riding are you really going to do?
- what are you willing to spend?
- what are the coldest temperatures you're going to ride in?
If you are an urban, fair-weather, short trip cyclist, your needs are simple: get a Planet Bike Turbo for the rear, and something with a white LED for the front. The PB Turbo even shows in sunlight, so run it if your route takes you through shadow or bad drivers: that is, anywhere. This set-up is cheap, reliable and removable: to avoid theft or to use on more than one bike. How bright is the Turbo? Bright! View the pictures and video at 'Biking in a Big City' to see.
I use both PB lights shown on the post at 'Biking in a Big City' on steady for urban
night riding: flash is too annoying. Also nice the two PB lights use
the same mount, which is nearly the same mount that the PB Sport Spot headlight uses. A very interchangeable system. The Sport Spot can also be headband or helmet mounted, but it is a be-seen light, so not bright enough to light up a road.
But what are you going to do about winter, if you ride in it? My experience matches the classic handbook, “Mountaineering, the Freedom of the
Hills”: alkaline batteries crap out before 0C, and NiMH rechargeables not much later. I have run regular batteries, NiCd and NiMH
rechargeables, and lithium, down to -30C. Lithium have the best
tolerance to cold, then in order of best to worst: NiMH, NiCd and
regular. At -30C you can only rely on lithium for taillights, but I have had a headlight lithium power pack mounted on my frame get too cold to put out power. Flashing also works better than
steady in that cold. Perhaps because the batteries cannot put out
the power for steady. More money than lithium batteries, a dynamo, or
batteries kept inside your clothing (usually a headlamp), is the best set up for winter. A good dynamo, like the Schmidt SON shown below, or the cheaper Shimano ones, can drive about 300 lumens at speed. Both dynamos, and keeping working batteries in pockets, are impractical for tail
lights, but practical for front lights.
For randonneuring or other rural night riding, any tail light on flash
should be good enough to be seen, or on steady not to dazzle other
cyclists. I’d use the Turbo for randonneuring, because a pair of AAA lithium batteries would get you through the night.
Then there is Reelight. No batteries. A ghetto-dynamo: powered off of spoke-mounted magnets. Only a be-seen light, but clever. Never tried them myself. Hmm... wonder why nobody's made a more powerful version so you could just use one of these to drive a front light, rather than have to use a dynamo hub? Oh, they have, but even the manky 'Magtenlight' is putting out only 100 lumens. I want triple.
*With 'HID' on this post I kept getting spam commercial comments. Comments on this post closed because of it. Not even about bike HID, but for cars. Damn, design a better spam-bot, assholes.