Just took them outside to play with; they are both basically the same light and same reflector (I put a SMO reflector in my F15).
To my eyes, the throw is very much the same with both lights. I could barely detect a slightly brighter hotspot in the XM-L, but you really had to pay a lot of attention to see it. What was WAY obvious was that everything around that hotspot was something like 50% brighter with the XM-L.
The C8/K8/F15 reflector is still not optimzed to focus the XM-L into a tight thrower. I think the shear size of the emitter is the primary cause of that, it bounces rays all around the reflective surface and they cannot stay focused as well as a smaller emitter can.
I wish I was better at night photography and had the time, I'd take some beam shots for comparison, but I think what we have seen in the past with P60 drop-ins also applies to the bigger reflectors. XM-L's throw about as far but light up a lot more real estate at 250 ft than an XP-G does. The little $8 Ultrafire focusable light I got on ebay throws about the same distance on a 14500 battery, but the hot spot is about 1/10th the size of the XM-L and 1/5 the size of the XP-G.
Now if someone can figure out how to get a really good focusable light for an XM-L, that might be worth investing in. It doesn't have to be laser-like tight, just more concentrated into the hotspot.
I’m waiting for the first recoil XML. I just got the SF Masterpiece Pro1 and that beam is focused super tight. The reflector is huge so I can imagine how big a reflector would have to be to focus an XML in the same manner. I think you could use a much smaller reflector in the recoil format. I know a focusing lens is not the answer.
DrJones did a pretty cool setup with a catfood can and one of the DX aspherics. I have the DX 75mm, a similar size round heatsink, a few cree samples and batteries. I just need to get my ass down to the hw store and get a 3" pipe fitting to make a giant "focusing" flashlight.
A 50mm aspherical lens on XM-L will still not outthrow say the dereelight XR-E/Tiablo A9 aspherical. It has to be much bigger, i suspect about 90-100mm size (big!). It has to do with surface brightness, emitter size as well as lens size.
It has to do with surface brightness, emitter size as well as lens size.
Of the three, I don't think it has to do with emitter size. Precision is also very important as even a very small misfocus can cost more light than a larger lens/refector.
I've always wonder how perfect of parabola a home satellite dish is. A "reflex" light with a headless flashlight as the source pointed at a mirror taped dish should vastly outdo those above.
I suspect that while an aspherical lens is probably not the route to an XML super-thrower a TIR optic may well be. The only experience I have of TIR is my Hugsby P2 (Q5). The P2, with a 16340 in it, throws every bit as well as my P60 XPG with SMO reflector.
A parabola of given height and diameter is unique; maybe a given reflector isn't perfectly parabolic though.
The better collimated you want your beam, the bigger the focal length has to be. To catch the same amount of light from the LED at a bigger focal length, the aperture diameter has to increase, too. That means better collimation (and thus better throw) requires a bigger diameter.
Spot intensity (and thus throw) depends mainly on 3-4 factors (I like to split the losses):
Effectively used apparent reflector area (disk area minus the 'dead hole' in the center),
LED luminance ("surface brightness"),
Losses due to absorption, scattering, reflection,
Losses due to reflector shape imperfections (including OP).
I start with (b): An XM-L U2 @3A has a lower luminance (b) than the XR-E R2 @1A; about 30% less. That means about 16% less throw in an otherwise identical setup with same area/losses/perfect reflector/etc.
The usually by far most important factor is (a), the area, i.e. the reflector diameter. Twice the diameter makes 4 times the area and thus 4 times the spot intensity, which in turn gives twice the throw.
Actually throw is directly proportional to the reflector diameter (with equivalent LED and quality). My measurements show that a well driven XM-L flashlight in a good SMO reflector has a (NEMA-)throw of around 8000 times it's reflector diameter. That factor depends on LED type, bin, current, heat-sinking as well as reflector quality including OP/SMO and alignment. OP or underdriven XM-L lights get a lower factor around 6000; small reflectors suffer less from OP. I call that factor 'relative throwiness'; it says how well a light uses it's reflector size. BTW, typical aspheric lens lights get values of 10000 to 13000.
Have you done calculations/measures of which kind of misalignment affects throw/focus more? Horizontal cross the reflector lens or away from/into the element?
I think axial displacement affects throw more, but I have not tested that, nor am I sure of it. May even depend on actual reflector quality/imperfections.