Hi Matt,
Flashlight regulation is circuitry that attempts to maintain steady light output as batteries wear. Some headlamps have it, most do not. Those that do not rely on the batteries themselves to supply a form of regulation, which generally speaking lithium and NiMH cells can accomplish and alkaline cells cannot.
The dirty little secret of any regulated light I've tested is that set on high with alkaline cells, the output curves show no sign of effective regulation. Some can pull this feat off in medium and low.
As I noted in this test, the Tikka XP and PT Eos lithium output curves are effectively identical, implying the regulation is provided by the batteries and not the Eos' circuitry. OTOH the Eos with lithiun on medium is a thing of wonder, and I suspect the long, long steady output is a happy marriage of both the batteries and the regulation.
Cheers,
Rick

