I never really liked the mediocre conversions to native LED 6v lanterns I've seen a few of them on with a handful of them and another looking like it had a single dropin I always thought having such a large lantern with a lot of power in the batteries with too little output and too much runtime was just not that great. I did see a single LED version that came out later that was D cell native I think it could use either 2 or 4 D cells maybe they run in sets of 2 cells in parallel.idk, those 6v lanterns that use leds instead of bulbs, are actually worse than bulbs, they are not much brighter, since they are sealed, they are driven by relatively low current, and they do not throw as well as bulbs, and blue tint is pretty bad. they may have runtime advantage, but i'm not even sure they do overall, most led 6v lanterns have no regulated drivers, most of the time they only have resistors. so it uses few watts of energy just to heat up a resistor. But unlike bulbs, leds draw becomes smaller and smaller as batteries drain. with bulbs not so much. so leds will run longer but at reduced output
As for the regulation back in the day these lanterns were mainstream.. even the LED models there were not any regulated LED lights out that I know of the lights that looked regulated was more of the battery itself than circuitry.
The wonderful thing about LEDs was sucking over 90% of the useful power out of batteries by continuing to give usable light from batteries that would have only given about maybe 60-70% of the power in incan lights before dimming and tint shifting to be unuseful.