I've seen pictures of the internals (I don't currently own a Solitaire) and there doesn't seem to be any regulation mechanism. At this price point and with the LED emitter it has, the light is almost certainly "regulated" by the LED taking its (fairly low) maximum current as long as the battery can supply it.

In other words, digital regulation for a single-mode light that runs a low current wouldn't make any sense.

At this price point the performance is impressive. Maglite has really good warranty service as well.