I've seen what you mean greenpond. Bright as in a dull yellow, near dead battery looking output to a "oh so this is what they're capable of" nice bright output by cleaning contact points, which lowers the resistance from a few ohms to less than one at times.
The older pre-Maglite setup became corroded over time. A bit of De-Oxit or Tarn-X could make my ohm meter do a happy dance after I was done. I restored a bunch of vintage flashlights that had sat in granpas attic somewhere in America for 75 years. Some did not work at all even though the copper contacts looked ok. Some burned dimly. A q-tip cleaning usually got the non working ones going and the dim ones nice n bright. Ok, instead a flickering surrounded by wax ready to snuff out candle look to holy crap, 5 birthday candles bright……
Or in the case of a Maglite all 20 lumens.
A lady my wife works with asked me to get a 2C going again. The bulb was burnt but… the switch was less than reliable. I disassembled it and saw all kinds of tarnish inside. Never having disassembled a Mag switch before I had trouble figuring out the order of things upon reassembly. I swapped in a new switch.
See, Maglite used to supply repair shops with kits. A kit came with like ten old style switches, ten new style, 12 lenses, 8 springs etc etc. I found a kit for C/D size at eBay for like $35. I also scooped up a minimag repair kit. So I ended up putting a new factory lens, new o'rings, spring and switch in that 90 something year old ladies light and gave it to my wife to return with instructions on how to take the spare bulb out of the tailcap and swap it into the light. I also donated 3-twin packs of bulbs.
Later I figured out how to reassemble the old switch, took it back apart to clean the metal and installed it into a 1980's light I had bought with a stuck battery. The light was mint on the outside but alkaleak from the top battery had murdered the switch assembly.
Last night I watched the movie "they shall never grow old" which is actual footage from world war 1 showing various events in the life of some British soldiers. While showing the footage there were voices of the soldiers in the footage describing what it was like for them on a daily basis. Really cool movie if you like that sort of stuff. Anyway, at times they'd show night footage and you could see just how bright a flashlight was in those days. I mean nothing like today, but for the time it was pretty amazing how well the new electric candle lit up a given area. Those scenes alone caused me to think the purchase price of the movie was worth it. Instead of wondering how bright a 1917 2C flashlight was capable of I saw actual footage and realized some of my old lights aint anywhere near as bright as they were when brand new.