Yes, I realize that. I did take shaped beams and their better efficiency into account when I mentioned a 5 watt headlight instead of my current 8.5 watt one.

However, in the case of taillights, the whole point of them is to smear light all over the place. I run a 3 watt main light and two 2 watt secondary lights. I don't always run all three lights so I figured 5 watts is a good number. I actually probably would only run the 3 watt on the dynamo since the whole point of having multiple lights is that so you can have an entire system fail and still have a light. For the same reason, even if I had a dynamo front light I'd still have to carry at least a hand torch and a lockblock. I've been stuck 4 miles from anywhere in the middle of a snowy, potholed gravel road in the middle of the woods at 4 in the morning before with a dead light, and it's NOT FUN. In that case I had no backup and wound up slowly making my way home by holding my taillight on steady mode in my hand. Also not fun.

As far as new lights being efficient, I suppose the Philips Saferide counts as a new, efficient light. It comes with 2300 mah batteries rated at 2 hours on high. That's 1.15 amps draw at 4.8 volts nominal, which is 5.5 watts power draw. A touch more than the 5 watts I mentioned above (where I was, admittedly, just pulling numbers out of a place).

In any case, if I continued to use a battery powered 2nd taillight, that's 8 watts of draw.

I did think of something else last night on my way home. A lot of the time in the winter (the only time I really need a light), I'm plowing through poorly plowed, rutted mush. I was doing so last night. When the conditions are like this, I'm only going about 7 to 9 MPH at best, sometimes 4 MPH, steering like mad and skidding the front wheel all over to muddle through the criss-crossing car wheel ruts, for 20 minutes at a time. And that's the time when I need the most light, because it's almost impossible to see the potholes through the rutty snow even with a bright light. Also the tail is doubly important on a road where even the cars are mooshing around all over, around bends and hills in the black with full tree cover.

Is a dynamo going to be able to deliver the power at 6 MPH to keep a 1000 lumen light and a 3 watt taillight going indefinitely? 20 minutes is too long to expect a standlight capacitor to hold.