Welcome to CPF!
Part of the confusion may come from the way manufacturers measure their lights' output. The first centers around the LED's bin. (If you're new to flashlights, LEDs are graded like diamonds and sorted into a "bin" according to how bright they are. See
http://home.comcast.net/~theledguy/bin_codes/index.htm for more info). So if the manufacturer is using a T-bin LED, which theoretically provides between 67-87 lumens, the manufacturer will probably ignore the lower end of the spectrum and claim, "our flashlight provides up to 87 lumens!"
Another possibility is that the manufacturer is just measuring "bulb lumens," which are higher than the actual lumens you see because some light is always lost on the way out of the flashlight. Although a bulb may initially put out 100 lumens, you lose some of that brightness when the light has to bounce off the reflector, pass through the lens, etc. (That's one reason Surefire uses high-quality lenses on its flashlights - they let more light through!) By the time you're done, your 100 lumen light may only actually be pushing 70 lumens out the front. Surefire's pretty good about measuring how much light *actually* comes out of their flashlights, but doing so requires expensive machinery (and gives you lower numbers, which the marketing people don't like!) So many manufacturers will just report their bulb lumens, which doesn't accurately reflect the amount of light you'd see in actual use.
So if we put this all together, look how crazy the numbers can get. Manufacturer X reads the bin code and says "hey, this provides up to 87 lumens; I'll just use that number." But in reality, if the flashlight has an underperforming T-bin that's only putting out 67 lumens (the bottom end for a T-bin), and the manufacturer is using a low quality lense and other components that reduce the transmission rate to only 75% of the bulb's rated lumens, our 87 lumen flashlight transforms - yikes! - into a 50 lumen flashlight. In other words, the "real world" brightness of this light is just over 1/2 the manufacturer's claim!
Part of the reason that Surefire is so respected is that they accurately report (and sometimes even understate) their flashlights' brightness. With them, you know that your 60 lumen flashlight will actually be putting out 60 lumens.
Other manufacturers who have pretty good reputations for accurate reporting are HDS (now Novatac), and Arc. And nearly all of the custom flashlight makers here on CPF (e.g. McGizmo) are well known for their honesty and careful reporting. As for the others, well...that's why we have sites like FlashlightsReviews.com - to keep the manufacturers honest! (This seems like an appropriate time to send out a quick thanks - "thanks!" - to QuickBeam, who runs FR.com). =)
Hope this helps!
- FITP