I was answering a question from cajampa in the XP-E2 Torch thread and while I was at it I dissected the F3 to see where the light losses go. I thought it was nice enough information to start a topic about.
The supfire F3 is (apart from the stock switch, I had to replace it with a small Omten plus do a spring bypass ) a well build 18650 zoomie with a relatively long focal length lens (so a lot of travel on the slider, a small hotspot and a big difference in light output between flood and throw).
The light is modded with a 2.10A AK-47C(6x7135 chips) lineair driver and a dedomed XP-E2 R3 1D0 led. I blackened the brown led-board-screw-in ring for a better beam when zoomed-in. In my integrating sphere I measured the -100% setting- light output 30 seconds after switch-on: fully assembled (slider in flood and throw setting), with the lens removed (slider in flood and throw setting), with the head removed, and with the screw-in ledboard-fastener removed. And last I already had the bare led output outside the flashlight on my cooled copper mount (although the cooling regime was a bit different on the mount compared to the after-30second-situation in the flashlight). These are the results:
complete zoom out:280lm minus lens 'zoom out': 231 lumen minus head: 381 lumen minus black ring: 413 lumen (and bare led: 427 lumen)
complete zoom in: 90 lumen minus lens 'zoom in': 81 lumen
Apart from these numbers I tried to single out the light loss by absorption/reflection of just the lens of the F3. I did that by holding a bare ledboard with a dedomed XP-E2 at the entrance of the sphere, and then again with a lens (held with a forceps) in front of it, in both situations making sure that the complete light-cone was entering the sphere (who said that I don't have steady hands , holding a lens at the tiny edge with a forceps, and the ledboard, and making a picture with my phone camera with my other hand, I did not drop the lens in the sphere!) . I measured twice, the measured light drop was 11% and 12% resp.
So now you know where all that light goes in this zoomie (if you did not expect that already): when zoomed out, from the 100% of the bare led output, 11% is absorbed by the black ring, 15% gets lost inside the head, 8% is absorbed/reflected by the lens, just 66% makes it out of the flashlight. The lens helps bending the light so that a bit more gets past the bezel, but it also absorbs/reflects some light. When zoomed in, the light that gets lost inside the head increases drastically, it is 65%, so including the 11% of the black ring and the absorption by the lens, just 21% of the light makes it out of the flashlight (although it is all in an intense narrow spot).
I don't think in other zoomies it is much different, although if they have shorter focal length lenses the light loss when zoomed-in is more limited.