. Even those that are buck-boost drivers often do not have constant output from the drivers hence the falloff in light output. If you look at the output curves they look suspiciously like the voltage curve of a li-po cell
Damn it. Lost a fairly long message, so I'll summarize it quickly.
Seems to me like it's more of a power supply issue than driver. If you try to output more than what the battery can output, your driver will always be at 100% on, ie there's no regulation taking place, and the output in the LED will follow that of the battery, regardless of the topology in use. This tendency can be seen in quite a few torches. I would be interested in seeing what happens to a BB TL2800p if you hook it up to a 4V 200W power supply.
In order to test this, you don't need tools to measure the output of the light. You just need an amp-meter to see what you're throwing in the LED and it will confirm your design. What comes out of the LED for a given current is not something you have control on anyway.
How relevant is all this technical stuff to divers? It isn't. What matters is that their lights *work*. From what I can see, the VL15000P is "better" (although less constant, yes, but really, I doubt photographers care about having 7500 or 7600 lumens) than the L&M Stella 7500. It also appears to be cheaper (but I couldn't compare on the same site, the difference was still significant at 1800$ for L&M and less than 1400 for BB).
So at the end of the day...