Just for fun, with all this talk about flashlights, minimum lumens, etc., I decided to flip this question on its head. (See how I spend a vacation day?:))

My question is what's the minimum number of lumens the human eye can actually see? That's the flashlight I want!

We know the human eye can reliably respond to an input of 90 photons arriving irregularly or a single photon arriving regularly, which we'll say reasonably corresponds to our definition of a flashlight. (D.A. Baylor, T.D. Lamb, K.W. Yau, "Response of retinal rods to single photons." Journal of Physiology, Lond. 288, 613-634. 1979.)

So, how to translate that to lumens?

Small numbers of photons will be detected scotopically by the rods in your eyes (as opposed to the cones), and each rod has a diameter of approximately 0.002mm, giving each an area of 0.0063mm^2.

Now, let's consider a 1 photon flashlight, sure to be coming to a store near you real soon now. (Can we get a Doug Ritter model???)

We'll suppose the photon has a frequency of 540nm, which would make it "greenish" on a larger scale.

Then, the rod would have an incidence of 2.39x10^13 photons per second per lumen. Working backwards, we have that a single rod can detect 4.18x10^-14 lumens, assuming the flashlight were outputing one photon/second.

And there ya go. So keep yer fancy 200 lumen lights! I'll be more than satisfied with my 0.00000000000004177 lumen model! (It probably runs for 100,000 years on a single battery. And if you're willing to use a radioactive battery, it can run for millions of years on a single "charge." Try that with your Surefire!)