comments based on what I've seen and believe to be factual:
The KL2 is current limiting which I believe is different than digital regulation??
The particular KL1 shown in the photo above on an E2 body, when hosted on an E1 (1 123 cell) is brighter than the 4 Arc LS's and 2 SLS's that I have tested. With variation from one Luxeon to the next, this isn't very useful information.
To the best of my knowledge, the current Arc LS is designed for a Vin from roughly 1.5 to 3 volts whereas the KL1 (possibly KL3) are designed for a Vin from 3 to 9 volts.
Relative efficiencies and lumen outputs won't be better understood until there is a reasonable population of these guys available to those of us who can and will compare notes as well as make some tests.
I would categorize the L1 as similar in size to the E2 but behavior comperable to a KL1 on an E1 with an additional feature of a single dim mode.
The A2 is in a class all its own and with digital regulation of the incandescent bulb coupled with the simpler resistive circuits for the LED's, we have apples, oranges and an new, unknown fruit here (damn tasty though)
- Don