Koyote

Hard to say, since they vary so much with the mode and with the temperature. With the Cygolites, my preferred mode is called (I think) "Zoom," which is a rather gentle flash -- the light gets steadily brighter until it hits max brightness, then dims until it is completely dark, over and over again. (It's a nice compromise between obnoxious, seizure-inducing flashing and a steady beam.) In this mode, you can only adjust the speed/frequency of the flashing in this mode, not the max brightness -- and subjectively, the 150lm model (five yrs old) seems to last longer than the 350lm light (six months old) even though the brightness seems about the same. Now that the weather is cold, I've had the 350 die on rides of under 3 hrs, while the 150 lasts only a bit longer.

I think the 350lm model, with its two LEDs, is not really much brighter than the 150lm model -- I think Cygolite is kind of fudging it, perhaps by adding together the lumen values of the two LEDs -- which, if I remember my physics, is not how it works.

My best bang-for-buck tail light is a 100lm Bontrager that I won at a race a few years ago. The lens gives a good focus for the beam, there are useful sidelights, and the battery life is still excellent.